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Bidirectional muographic measurements were conducted at the Imashirozuka burial mound, Japan. The mound was built in the beginning of the 6th century as a megalithic tomb and was later collapsed after a landslide caused by the 1596 Fushimi Earthquake, one of the largest earthquakes that have occurred in Japan over last few centuries. The measurements were conducted in order to find evidence of this past disaster recorded in this historical heritage sites. As a result, the vertical low-density regions were found at the top of the mound. These regions were interpreted as large-scale vertical cracks that caused the translational collapse process behind the rotational landslide that was already found in the prior trench-survey-based works. These results indicate that there was an intrinsic problem with the stability of the basic foundation of the Imashirozuka mound before the 1596 Fushimi Earthquake. [ABSTRACT FROM AUTHOR]

Natural fault networks are geometrically complex systems that evolve through time. The evolution of faults and their off-fault damage pattern are influenced by both dynamic earthquake ruptures and aseismic deformation in the interseismic period. To better understand each of their contributions to faulting we simulate both earthquake rupture dynamics and long-term deformation in a visco-elasto-plastic crust subjected to rate-and-state-dependent friction. The continuum mechanics-based numerical model presented here includes three new features. First, a 2.5-D approximation to incorporate effects of a viscoelastic lower crustal substrate below a finite depth. Second, we introduce a dynamically adaptive (slip-velocity-dependent) measure of fault width to ensure grid size convergence of fault angles for evolving faults. Third, fault localization is facilitated by plastic strain weakening of bulk rate-and-state friction parameters as inspired by laboratory experiments. This allows us to for the first time simulate sequences of episodic fault growth due to earthquakes and aseismic creep. Localized fault growth is simulated for four bulk rheologies ranging from persistent velocity-weakening to velocity-strengthening. Interestingly, in each of these bulk rheologies, faults predominantly localize and grow due to aseismic deformation. Yet, cyclic fault growth at more realistic growth rates is obtained for a bulk rheology that transitions from velocity-strengthening friction to velocity-weakening friction. Fault growth occurs under Riedel and conjugate angles and transitions towards wing cracks. Off-fault deformation, both distributed and localized, is typically formed during dynamic earthquake ruptures. Simulated off-fault deformation structures range from fan-shaped distributed deformation to localized Riedel splay faults. We observe that the fault-normal width of the outer damage zone saturates with increasing fault length due to the finite depth of the seismogenic zone. We also observe that dynamically and statically evolving stress fields from neighboring fault strands affect primary and secondary fault growth and thus that normal stress variations affect earthquake sequences. Finally, we find that the amount of off-fault deformation distinctly depends on the degree of optimality of a fault with respect to the prevailing but dynamically changing stress field. Typically, we simulate off-fault deformation on faults parallel to the loading direction. This produces a 6.5-fold higher off-fault energy dissipation than on an optimally oriented fault, which in turn has a 1.5-fold larger stress drop. The misalignment of the fault with respect to the static stress field thus facilitates off-fault deformation. These results imply that fault geometries bend, individual fault strands interact and that optimal orientations and off-fault deformation vary through space and time. With our work we establish the basis for simulations and analyses of complex evolving fault networks subject to both long-term and short-term dynamics. [ABSTRACT FROM AUTHOR]

The analysis of earthquake time series in a new time domain termed natural time enables the uncovering of hidden properties in time series of complex systems and has been recently employed as the basis of a method to estimate seismic risk. Natural time also enables the determination of the order parameter of seismicity, which is a quantity by means of which one can identify when the system approaches the critical point (the mainshock occurrence is considered the new phase). Applying this analysis, as an example, to the Japanese seismic data from 1 January 1984 until the super-giant M 9 Tōhoku earthquake on 11 March 2011, we find that almost 3 months before its occurrence the entropy change of seismicity under time reversal is minimized on 22 December 2010, which signals an impending major earthquake. On this date the order parameter fluctuations of seismicity exhibit an abrupt increase. This increase is accompanied by various phenomena; e.g., from this date the horizontal GPS azimuths start to become gradually oriented toward the southern direction, while they had random orientation during the preceding period. Two weeks later, a minimum of the order parameter fluctuations of seismicity appears accompanied by anomalous Earth magnetic field variations and by full alignment of the orientations of GPS azimuths southwards leading to the most intense crust uplift. These phenomena are discussed and found to be in accordance with a physical model which seems to explain on a unified basis anomalous precursory changes observed either in ground-based measurements or in satellite data. [ABSTRACT FROM AUTHOR]

Eruptive rates in volcanic arcs increase significantly after subduction mega-thrust earthquakes. Over short to intermediate time periods the link between mega-thrust earthquakes and arc response can be attributed to dynamic triggering processes or static stress changes, but a fundamental mechanism that controls long-term pulses of volcanic activity after mega-thrust earthquakes has not been proposed yet. Using geomechanical, geological, and geophysical arguments, we propose that increased eruption rates over longer timescales are due to the relaxation of the compressional regime that accompanies mega-thrust subduction zone earthquakes. More specifically, the reduction of the horizontal stress σh promotes the occurrence of short-lived strike-slip kinematics rather than reverse faulting in the volcanic arc. The relaxation of the pre-earthquake compressional regime facilitates magma mobilisation by providing a short-circuit pathway to shallow depths by significantly increasing the hydraulic properties of the system. The timescale for the onset of strike-slip faulting depends on the degree of shear stress accumulated in the arc during inter-seismic periods, which in turn is connected to the degree of strain-partitioning at convergent margins. We performed Coulomb stress transfer analysis to determine the order of magnitude of the stress perturbations in present-day volcanic arcs in response to five recent megathrust earthquakes; the 2005 M8.6, 2007 M8.5, and 2007 M7.9 Sumatra earthquakes; the 2010 M8.8 Maule, Chile earthquake; and the 2011 M9.0 Tohoku, Japan earthquake. We find that all but one the shallow earthquakes that occurred in the arcs of Sumatra, Chile and Japan show a marked lateral component. We suggests that the long-term response of volcanic arcs to subduction zone mega-thrust earthquakes will be manifested as predominantly strike-slip seismic events, and that these future earthquakes may be followed closely by indications of rising magma to shallower depths, e.g. surface inflation and seismic swarms. [ABSTRACT FROM AUTHOR]

The article presents a study that determines the high resolution tomographic images of the crust and upper mantle in and around the area of the 2011 Iwaki earthquake and the Fukushima nuclear power plant in Japan. It reveals that the Iwaki earthquake was triggered by the ascending fluids from the Pacific slab dehydration and the stress variation induced by the Tohoku-oki mainshock. It suggests strengthening the security of the nuclear power plant site to withstand potential large earthquakes.

This abstract illustrates major results obtained from the questionnaire survey carried out in Kesennuma on October 2018. We conducted a questionnaire survey focusing on the lifestyles of young migrants living in Kesennuma. The questionnaire was carried out through the Internet using the Google Form. The questionnaire consists of three parts: 1) attitude toward work, income and time management, 2) use of the Internet and 3) interaction with local people. Kesennuma is the region where greatly damaged by the tsunami caused by the Great East Japan Earthquake occurred in 2011. Many volunteers visited this tsunami-hit area and spent days in reconstructing the area with the local people. Among those volunteers, a certain number of young people decided to migrate from other parts of Japan to the tsunami damaged area. Some left their jobs and found a new job in this area, some after graduating universities started new business, and some returned to their parents' home to help them. Since then, they have been working continuously in many ways, with the local people in order to revitalize the tsunami-hit area, especially in Kesennuma. The objective of the questionnaire was to find out the reasons why those young people decided to migrate from other parts of Japan and settle down in this local area. The questionnaire was distributed to those young migrants in Kesennuma area who contacted with the Kesennuma Centre for Migration and Settlement. We received answers from 108 young migrants, and the response rate of the questionnaire was 87%. This number is extremely high compared to common questionnaire response percentage. We focused on the three topics of the questionnaire, namely Q1: Are you satisfied with your life here?, Q2: How many hours do you use the Internet per day? Q3: How far do you visit your local acquaintances? Q1: Are you satisfied with your life here? As for life as a whole here, the percentage of those answered "very satisfied" and "fairly satisfied" reached 89% of the respondents. In addition, we found that 57% of respondents answered "very satisfied" with the social relationship with local people. Q2: How many hours do you use the Internet per day besides your office hours? The answers to this specific question are shown in Figure 2. First of all, the very high response rate of the questionnaire clearly tells that these young migrants were well connected with each other through the Internet. Fifty-three percentage of them answered that the average hours of using the Internet per day is more than two hours besides their usage at their work. Fifteen percentage of them have more than 701 followers to their Facebook, this percentage appears to be much higher than an average number. This heavy use of the Internet is very contrasting to the fact that at the same time, they answered that they enjoyed and valued very highly the face-to-face social relationship with local people. Q3: How far do you visit your close local acquaintances? The above two facts motivated us to ask, how often and how far they travelled to visit their nearest local acquaintances. Surprisingly enough, 44 % of them answered that they had daily interaction with local acquaintances such as visiting each other and had chat over a cup of tea, not only exchanging a few words. If we add those who visited local acquaintances two or three times a week, the percentage exceeds 65. It is easy to imagine that they were very much involved with the local people and the area. The average walking time to the nearest local acquaintance was two minutes and forty-three seconds, while those going by car, their average travel time was ten minutes and six seconds. In order to see the spatial interaction between migrants and locals people, we tried to obtain their home addresses. But due to the protection of personal information, we obtained the location data of centres of the districts where they resided and a few of the home addresses. Figure 3 illustrates the nearest local acquaintance distribution with the buffer zone of 217 metres from each location. Note that the travel distance was estimated from [two minutes and forty-three seconds] multiplied by [80 metres: an average walking time per minute]. From the above results, we conclude that two aspects are important for young migrants' preferable daily life, namely, 1) local and intimate connection with local people, and 2) global connection with many friends through the Internet. These two aspects are contrasting to each other, but both are indispensable at the same time. As for the GIS map, we use National Geographic Base Map downloadable from the Geospatial Information Authority of Japan, Japanese GSI website for English is http://www.gsi.go.jp/ENGLISH/index.html. Also for the census data, we downloaded from statistics GIS of e-Stat, a portal site for Japanese Government Statistics whose English website is https://www.e-stat.go.jp/en. Acknowledgement: This questionnaire survey is part of a project supported from the Suntory Foundation on Collaborative Research on Community Cultural Activities. We thank the Foundation. [ABSTRACT FROM AUTHOR]

The Great East Japan Earthquake in 2011 made a realization of non-Japanese living dispersed in various areas across Japan. The non-Japanese trainees working in the small-size factories in the underpopulated areas and the immigrant wives married to Japanese men in the farming areas were there to compensate for the decreasing Japanese working-age population and the decreasing number of Japanese women who will marry farmers. These women, mostly Chinese and Filipino, live in local communities, isolated from the other non-Japanese residents; they cannot use their mother tongue, they cannot get mutual helps, and they cannot form ethnic community. Their distribution pattern is very different from that in foreigner-concentrated areas in metropolises like Tokyo and Osaka. Ethnicity studies in geography and sociology have mainly focused on foreigner-concentrated areas. There have been few studies on ethnic minorities who live dispersed among their host society. They have been invisible in Japanese society. This study try to clarify where in Japan non-Japanese are living dispersed and develop the method to measure how sparsely they are scattered. This study analyses the distribution pattern on non-Japanese by using the Grid Square Statistics of 2010 Population Census and GIS. The Grid Square Statistics is one of the small area statistics which divides the whole area of Japan into small mesh. This study uses statistics of 1km x 1km grids (Figure 1). So far, we have seen that the degree of the isolation of the non-Japanese woman is remarkable in north-eastern Japan. For example, among the 3,249 inhabited grids of Yamagata Prefecture, 1,291 of which had non-Japanese residents, 509 had only one non-Japanese, and 479 of those 509 non-Japanese were women. In other words, 15.7% of the one-squarekilometre inhabited grids in Yamagata Prefecture had only one non-Japanese resident and that person was female, which is the highest among 47 prefectures in Japan. On the other hand, this ratio was relatively low in the metropolitan areas including Kanagawa prefecture and the prefectures of southwestern Japan (Figure 2). This study identifies the grid which have only one non-Japanese and that person is female as "isolated-grid". In the isolated-grids, there are grids where no foreigners live in the 8 adjacent grids, which could be named as "more-isolatedgrid" (Figure 1). When we calculate the proportions of the grids for each prefecture and draw them with Quantile classification (Figure 3, left), isolated-grids are distributed in eastern Japan such as Tohoku region same as Figure 2. On the other hand, more-isolated-grids are found not only in eastern Japan but also in western Japan such as Kyushu (Figure 3, right). This is a new finding that has never been said before. [ABSTRACT FROM AUTHOR]

This study visualized the spatio-temporal changes in the tsunami inundation area and analyzed its expansion mechanism. The most characteristic of the Great East Japan Earthquake is the damage caused by the tsunami. And 90% of the dead was caused by it. One of the factors is that the preparation of countermeasures corresponding to the huge tsunami was not fully prepared. Therefore, after the Great East Japan Earthquake, the Japanese government has emphasized the importance of the advance preparation of the hugest tsunami expected. According to the past experience the occurring of huge tsunami is very rare. Earthquake researchers have observed same scale tsunami in every 1000 years in Japan. According prediction, next huge tsunami may be happened around the 2030. Therefore, analyzing the tsunami inundation mechanism of the Great East Japan Great Eastern is important for the future tsunami countermeasure. The arrival time and spatial distribution of tsunami inundation can be considered as a main important component of evacuation planning. In addition, a wide range of inundation area caused by huge tsunami is suitable for analyzing the inundation mechanism compared with a small-scale tsunami inundation. In this study I would like to examine the tsunami inundation process caused by the Great East Japan Earthquake in 2011. The method is as follows. First, movies shooting the tsunami inundation are collected from DVDs and TV hosting services. And they are examined as analysis materials. As a result, movies that taken from the ground were impossible to shoot the dynamic process of tsunami flooding. So that movies that taken from the helicopter or airplane was selected in this research. Next, the movies are converted into images at regular intervals of time. And adding position information to images (geo-reference), images are imported on the geographic information system (GIS). After that, Inundation limit lines are digitized. In this study, inundation limit lines are created at intervals of around 5 seconds. However, when the image is disturbed by dust etc., images of around 5 seconds are used. Basic information on the tsunami inundation handled in this study is shown in Table 1 and Figure 1. As the result, tsunami inundation process was strongly affected by the location of buildings (Figure 2). On the other hand, the inundation distance declined even where the fields spread. The spatio-temporal variation of the inundation process was quantitatively clarified. Regression analysis was performed with variables of inundation time and inundation distance. As a result, changes in correlation were observed in a certain section. In order to analyze the factors, two regression analyses were conducted. First is the inundation time and elevation as variables. Second is the inundation time and distance from buildings as variables. The building data had acquired the image before the earthquake (April 4, 2010) from Google Earth, and created the building shape data. As a result of each analysis, it became clear that sections where the elevation suddenly changes and the short distance from buildings, overlapped sections where the inundation distance does not extend (Figure 3). These results suggest that it is possible to predict inundation time and distance in other areas if parameters can be acquired. [ABSTRACT FROM AUTHOR]

The Mw ≥ 9.0 1952 Kamchatka, 1957 Aleutians, 1960 Chile, 1964 Alaska, 2004 Sumatra, and 2011 Japan earthquakes triggered destructive tsunami rupturing hundreds of kilometers along few specific segments of the subduction margins globally in a while. Such infrequent mega-events had shown their far-reaching effects and perplexed the world community. The 2004 mega-event in association with few other great earthquakes in the central and southern parts of the Sumatra margin (e.g., 1797 M ~ 8.4, 1833 M ~ 9.0, 1861 M ~ 8.5, 1905 Mw ~ 8.4, 2005 Mw 8.7, 2007 Mw 8.5) provided unprecedented opportunity for a critical reappraisal of hazard for the adjoining areas. We explore here the characteristics of seismic energy released along the eastern subduction margin, based on USGS catalogue for the period between 1976 and 2013. We consider the earthquakes with body wave magnitude 4.0 and above. We find the earthquake activities are mainly concentrated in four tectonic domains: first one covers the entire Myanmar margin (Segment I), second one includes Andaman-Nicobar-Northwest Sumatra margin (Segment II), third one is located in the Southeast Sumatra-West Indonesia (Segment III), and the fourth domain lies in the East Indonesia (Segment IV). The tectonics parameters, locations, great earthquake occurrences, seismic energy release, and the Wadati-Benioff zone geometry in these four segments also display distinct features. We find the aftershock activities of 2004 mega-event has been shifted from deeper to shallower level of the lithosphere in Segment II. The shifting of aftershocks of the 2005 Mw 8.7 Nias earthquake from deeper to shallower part of the subducting oceanic lithosphere was also noticed. Such shifting of seismicity towards the trench-axis after the 2004 MW > 9.0 earthquake was apparently caused by migration of the stress-field from deeper to shallower part of the Indian lithosphere. Similar shifting of aftershocks were also observed along the Kuril trench after the incidence of 15th November 2006 Mw 8.3 earthquake, and interpreted to be caused by stress transfer through the subducting lithosphere. Further, the energy bursts happened near the Northwest Sumatra and Car Nicobar areas are likely located in the zone of seismic quiescence during 2004 event. We find spikes in the plot of seismic energy distribution, which apparently indicates the stress energy transferring happened from east to west, towards the zone of occurrence of 2004 Mw>9.0 earthquake during the quiescence period. The b-values show a constant decrease in Segments II, III, and IV, whereas the Zone I does not show any such pattern prior to the 2004 mega-event. These typical observations account for dominant stress accumulation near the Sumatra area. We thus believe that the occurrence of 2004 mega-event was apparently concealed behind the long-term seismic quiescence existing near the Sumatra and Nicobar margin. A systematic study of the patterns of seismic energy release and b-values, and the long-term observation of collective behavior of the margin tectonics, might had given clues for the forecasting of the 2004 mega-event, and thus contribute to improve seismic hazard estimates.Keywords: Eastern Subduction Margin; Seismic b-value; Tsunami; Seismic quiescence; 2004 mega-event [ABSTRACT FROM AUTHOR]

Inundation by the 2011 Tohoku-oki tsunami flooded wide areas of coastal land in the Aomori Prefecture (Northern Japan). Once the 6-10 m high waves overflowed the 4.5 m high coastal defense walls at Oirase sensitive infrastructure was damaged, releasing pollutants into the nearfield environment. At the Momoishi-industrial park in Oirase the tsunami damaged multiple companies during the event and the ponding effect afterwards. Possibly two waves can be documented in the sedimentary record. With maximum thicknesses of 10 cm, fining upward sequences, rip-up clasts, mud caps and other sedimentary features these deposits present well preserved examples of tsunami deposits. This archive is best suited for a complementary organic geochemical analysis of the anthropogenic pollutants that were released by the neighboring factories. Cores were taken in an increasing distance from the factory starting from 10 m to 200 m. Close to the factory a strong increase of organic pollutants, such as polycyclic aromatic hydrocarbons, can be detected within the tsunami deposit. Reforestation efforts to replace destroyed sections of the coastal control forest, however, lead to the loss of parts of this 2011 tsunami archive. This increases the importance to sample and analyze these disappearing deposits, to gain a better understanding of the 2011 Tohoku-oki tsunami. This information will lead to a better hazard mitigation, reducing the destruction and the consideration of steps that need to be taken to diminish the associated pollution by the tsunami. [ABSTRACT FROM AUTHOR]

In recent years many devastating earthquakes with Mw ≥ 7.5 occurred during 2017-2018 asa result of active plate interactions near the major mega-thrust subduction zones. Theyreveal tectonic complexities and astonishing deformation styles associated with theplate movements. In this study, we determined source mechanism parameters andfinite-fault slip distribution models of four destructive earthquakes (Mw ≥ 7.5) byperforming point-source and finite-fault slip inversions. The shapes and amplitudesof long-period and broad-band P- and SH-waveforms recorded by the Federationof Digital Seismograph Networks (FDSN) and the Global Digital SeismographNetwork (GDSN) stations in the distance range of 30˚ - 90˚ are compared withsynthetic waveforms. Finite-fault slip models of earthquakes are estimated by applyinga hybrid back-projection method that uses teleseismic P-waveforms to integratethe direct P-phase with reflected phases from structural discontinuities near thesource. Overall results indicate various faulting mechanisms at relatively shallowfocal depths (h<70 km). For example, the February 25, 2018 Papua New Guinea(Mw: 7.5) earthquake indicates a thrust faulting mechanism associated with theconvergence of Australia and Pacific Plates. The September 28, 2018 Sulawesi (Indonesia)earthquake (Mw: 7.5), occurred within the Molucca Sea micro-plate at the eastern part ofIndonesia shows a strike-slip faulting mechanism reflecting the complex deformationsrelated to the interactions between Australia, Sunda, Pacific and Philippine Seaplates. Regardless strike-slip mechanism involved, this large earthquake producedunexpected tsunami waves along the coastal planes of Sulawesi. Finite-fault slipmodels reveal several heterogeneous rupture propagations and slip distributions onfault planes of those earthquakes. In addition, distributions of P- wave first motionpolarities recorded at near-field and regional seismic stations are consistent withthe best-fitting minimum misfit source mechanism solutions of earthquakes. Thisstudy is partially supported by the Turkish Academy of Sciences (TÜBA-GEBIP). [ABSTRACT FROM AUTHOR]

Displacement data produced by GNSS observations never saturate for large tsunamigenic earthquakes in contrast to seismometer data that has a limitation of instrument saturation. Geospatial Information Authority of Japan has launched a real-time GNSS analysis system named "REGARD" which estimates finite fault models based on the Japanese nationwide GNSS network GEONET. The REGARD system is designed to provide finite fault models including single rectangular fault and slip distribution models in a few minutes.The system is comprised of three subsystems: (1) Real-time positioning subsystem, (2) Event detection subsystem, and (3) Fault model inversion subsystem. The real-time 1 Hz data from the GEONET stations are analyzed by Real-time positioning subsystem using RTKLIB 2.4.2 software (Takasu, 2013) as the positioning engine. The processed time-series data are monitored by Event detection subsystem to detect earthquake events. EEW messages are also checked for complement of much noisier GNSS data. Once an earthquake event is detected, Fault model inversion subsystem is launched and finite fault models are estimated automatically. The finite fault models include single rectangular fault model, which is applicable to both inland and subduction zone earthquakes, and slip distribution model, which is particularly suitable for large subduction zone earthquakes.The REGARD system has been in operation since April, 2016. The REGARD system is processing ~1,200 stations of GEONET. In this presentation, we introduce an overview of the system design and show the test results for the cases of the 2011 Tohoku earthquake (Mw 9.0) and a simulated Nankai Trough earthquake (Mw 8.7). Furthermore, an operational real-time result for the 2016 Kumamoto earthquake (Mj 7.3) is also shown.The test results showed that reliable finite fault models for the earthquakes could be provided within 3 mintues for rapid tsunami simulations. The result for the 2016 Kumamoto earthquake (Mj 7.3) showed single rectangular fault models with VR of 96.2%, demonstrating the capability for modeling inland earthquakes. These results imply the possibility of improvements in tsunami simulations or hazard information using rapid finite fault models. [ABSTRACT FROM AUTHOR]

Japan is located at the boundary of the plate, so damage to the earthquake and tsunami often occurs. A large-scale earthquake is occurring in Tohoku in 2011, Kumamoto in 2016 and Osaka in 2018. Even in Fukuyama City, Hiroshima Prefecture where we live, earthquakes due to the Nankai Trough are expected. Since there have not been large-scale seismic activity by the Nankai Trough for more than 60 years, earthquakes may occur in the near future. So, I carried out lessons of the following three themes. 1) Why do earthquakes occur? 2) What kind of damage will be caused by the earthquake? 3) What can we do to prepare for the damage of the earthquake? The students made groups of five or six people, studied each theme, and made a presentation. In the first theme, the mechanism of plate tectonics was announced from each group. In the next theme, we reported damage caused by the earthquake, such as fault, tsunami, liquefaction phenomenon, fire, etc. In the final theme, I reported using a hazard map to understand the dangers of disasters caused by earthquakes and tsunamis occurring in familiar areas, and to prepare for disaster reduction to reduce damage more. Based on these presentations, we created a hazard map of Fukuyama city with our own arrangement.Through this lesson, I was able to imagine the damage caused by the earthquake not happening in distant places but the things that can happen around them. And when the earthquake occurred, I was able to conscious of preventing damage and minimizing damage. In Japan where earthquakes occur frequently, it became a class to propose how we should spend. [ABSTRACT FROM AUTHOR]

Along the Japan trench, quasi-periodic slow slip was found from repeating earthquakes (repeaters) and on-land GPS data before the 2011 Tohoku-oki earthquake. After the earthquake, the occurrence of Very Low Frequency Earthquakes (VLFEs) was recognized and new GPS-Acoustic (GPS-A) stations were deployed along the shallow plate boundary. In this study, we examine the postseismic activity of the slow slip from repeater, GPS-A and VLFE data. The repeaters are selected form their inter-event waveform similarity and the VLFEs are selected by waveform similarity with template matching at low-frequency range (0.02 – 0.1 Hz). Both data analysis periods were extended from previous studies to until the end of 2016. The GPS-A data from 2012 to 2016 was also re-analyzed to obtain better positions by incorporating the effect of horizontal variations in the sound speed of the ocean. The repeater analysis shows that the plate-boundary slip rate in the area close to the trench off Sanriku (to the north of the coseismic slip area) has large temporal variations with overall decay after the Tohoku-oki earthquake. On the other hand, the slip rate decreased monotonically with time in the area close to the trench off Fukushima (to the south of the coseismic slip area). In the off-Sanriku area, a slip-rate peak in 2015 correlated well with an active period of the VLFEs and a period of trenchward movement of the GPS-A stations. These observations suggest the occurrence of episodic slow slip caused the surface trenchward movement and repeater and VLFE activities. The amount of the inferred fault slip from the repeater activity was ~27 cm for the 2015 event, consistent with the seafloor GPS-A station movements (7~16 cm). The largest 5 earthquakes in the region during the 2015 episode were M5.5 to 6.9, but the total surface deformation expected from these earthquakes is too small (~2 cm) to explain the GPS-A station movements. This suggests the event was mostly aseismic. We also found the distribution of the VLFEs and repeaters are spatially complementary, suggesting that variations in local fault material properties near the plate boundary control the differences in slip mode. [ABSTRACT FROM AUTHOR]

The FORMOSAT-3/COSMIC (F3/C) radio occultation (RO) technique vertically scans the atmosphere from 0 to 800 km altitude over eastern Asia and the Pacific Ocean during the 2011 Mw9.0 Tohoku earthquake and tsunami. The mean wavelet spectra derived from dozens of atmospheric and ionospheric RO sounding profiles within ten hours after the earthquake illustrate that the atmospheric oscillations with a vertical wavelength ranging from 0.5 to 8 km and from 10 to 40 km, respectively, appear in the stratosphere and ionosphere within 6 hours after the earthquake initial rapture. The vertical wavelength estimated from the atmospheric gravity wave dispersion relation is compared with the observed vertical wavelength. The small-scale gravity waves may not be easy to reach the upper ionosphere. These RO-observed long-lasting atmospheric and ionospheric oscillations may consist of the earthquake/tsunami wavefront and its residual oscillatory tail. The results suggest that the RO technique is a powerful tool which is suitable for probing earthquake/tsunami-induced oscillations in the atmosphere, and allow a more comprehensive understanding of the excitation, propagation, and dissipation of earthquake/tsunami-induced gravity waves in the entire atmosphere. [ABSTRACT FROM AUTHOR]

Due to a serious disaster caused by the 2011 Tohoku-oki tsunami, improvement of the tsunami forecast has been an urgent issue in Japan. National Institute of Disaster Prevention installed a cable network system of earthquake and tsunami observation (S-NET) at the ocean bottom along the Japan and Kurile trench. This cable system includes 150 pressure sensors (tsunami meters) which are separated by 30 km. The system is the densest tsunami observation network in the world. Real-time tsunami forecast has depended on estimation of earthquake parameters, such as epicenter, depth, and magnitude of earthquakes. Recently, we developed a tsunami simulation method assimilating ocean bottom pressure data near tsunami areas for tsunami forecast (Tanioka 2018, Tanioka and Gusman 2018). The method does not need any tsunami source information nor earthquake source information. The method uses only initial parts of observed waveforms at ocean bottom pressure sensors. Therefore, the under-estimation of forecast tsunami heights due to the under-estimation of earthquake source or tsunami source should be prevented. However, it was tested only for an equally distributed ocean bottom sensor network (with a 30 km separation). This is not realistic because we do not have such an equally distributed network along the Japan and Kurile trench. In this paper, the 150 ocean bottom pressure sensors were located at exact positions of the S-NET sensors. We developed an interpolation method of observed heights at the S-NET sensors to create data at equally distributed stations with a 10 minute (about 18 km) separation. Then, we applied the tsunami simulation method assimilating those data for the 1968 Tokachi-oki earthquake case. First, the tsunami waveforms at the S-NET stations were numerically computed from a simple rectangle source model of the 1968 Tokachi-oki earthquake (Mw8.2). The fault parameters, strike=156, dip=20, rake=38, were obtained from the previous studies. The fault length of 200 km, the fault width of 100 km, and the slip amount of 4 m, are assumed. By using those computed tsunami waveforms as observation data at the S-NET stations, the tsunami numerical simulation with the assimilation was carried out using the assimilation method in this study. Those computed tsunami wave fields from the method were compared with those computed directly from the earthquake source model. The tsunami heights are slightly overestimated by the assimilation. The wavelength of tsunami from the assimilation method were slightly larger than those directly from the earthquake source model. The result suggests that the tsunami wave fields from the assimilation were overall similar to those from the earthquake source model. However, it also suggests that we may need more stations to improve an accuracy of the tsunami forecast. [ABSTRACT FROM AUTHOR]

Although interseismic locking distributions have been used in qualitatively evaluating the future earthquake potential, quantitatively estimating how an earthquake may rupture through the locked interface is a more useful tool for quantifying both seismic and tsunami hazards. Here, we investigate rupture scenarios from interseismic locking models along the megathrust interface below Nicoya peninsula, Costa Rica using spontaneous rupture simulations. We first estimate initial stress from locking, then initiate spontaneous ruptures at different nucleation points and observe the eventual earthquake magnitudes and slip distribution. We find that ~40% of nucleations tested develop into large earthquakes of Mw>7.2 based on present interseismic locking models. Of these events, those nucleated from deeper depths have a tendency for larger-amplitude shallow slip, suggesting increased tsunami potential. Furthermore, irrespective of the input locking models we do not observe rupture scenarios of earthquakes with intermediate magnitudes between 6 and 7, a result consistent with observations outside of the aftershock period in Nicoya. The results of hypocentre-dependent earthquake magnitudes and tsunamigenic potential not only pose challenges in estimating rupture extents from locking models, but also underscore the significance of quantitatively evaluating seismic and tsunami hazard in subduction zones. [ABSTRACT FROM AUTHOR]

Slow Slip Events (SSEs) are episodic slip events that play a significant role in the moment budget along subduction megathrust. They share many similarities with regular earthquakes, and have been observed in major subduction regions like, for example, Cascadia, Japan, Mexico, New Zealand. They show striking regularity, suggesting that it might be possible to forecast their size and timing, but the prediction of their extension and exact timing is still yet to come. They certainly are a great natural system to study how friction works at scale of the order of hundreds or thousands of km, and their recurrence time being much shorter than that of regular earthquakes, they give us the possibility to study multiple cycles and test their predictability. Here we focus on the Cascadia region, where SSEs recur every about 1 or 2 years, depending on the latitude. We use a catalog containing dozens of SSEs derived from the study of GPS position time series during the time span ranging from 2007 to 2017. The data show a clear segmentation with a few major patches interacting with one another, a behavior that recalls that of a discrete body system. We use both classical embedding theory and Extreme Value Theory applied to the study of dynamical systems to show that, where the Signal to Noise Ratio is sufficiently high, a low-dimensional (< 5) non-linear chaotic system is more appropriate to describe the dynamics than a stochastic system. We calculate major properties of the strange attractor like its correlation and instantaneous dimension, its instantaneous extremal index and a possible range for the metric entropy of the system. This knowledge is important for the determination of the predictability of the system, since it is related to the rate at which two trajectories in the phase space diverge. We further validate our results with a fuzzy inference system model to check the predictability of the slip and slip rate. In conclusion, SSEs in Cascadia can be described as a deterministic, albeit chaotic, system rather than as a random process. As SSEs might be regarded as earthquakes in slow motion, regular earthquakes might be similarly chaotic and predictable. [ABSTRACT FROM AUTHOR]

On September 28, 2018, a magnitude Mw 7.5 earthquake occurred in the neck of Sulawesi's Minahasa peninsula. The combined effects of the earthquake and tsunami caused catastrophic damage and more than 2000 deaths. An international tsunami survey team (ITST) was deployed 3 weeks after the event to document flow depths, runup heights, inundation distances, sediment deposition, damage patterns at various scales, performance of the man-made infrastructure and impact on the natural environment. The 23 to 29 October ITST covered a 100 km stretch of coastline circling the entire Palu Bay and adjacent coastlines along the Makassar Strait. A 200 km long reconnaissance flight with an Indonesian Army Mil Mi-17 helicopter provided oblique aerial photography of impacted sites. The collected field survey data includes 130 tsunami runup and flow depth measurements. The tsunami impact peaked inside Palu Bay with flow depths above ground reaching 6 m and maximum runup heights exceeding 10 m. Inundation and tsunami damage was mostly limited to within 0.5 km of the shoreline except along rivers. A rapid decrease of tsunami heights was observed towards the bay entrance and outside of the Palu Bay along the Makassar Strait coastlines. Two tsunami eyewitness video recording locations inside Palu Bay were surveyed for subsequent video image calibration, tsunami hydrograph and flow velocity analysis. We deployed a Leica BLK360 scanner from the NHERI RAPID facility. We acquired precise topographic data using terrestrial laser scanning (TLS) at selected video sites with multiple scans acquired from different instrument positions. These ground-based LiDAR measurements produce 3-dimensional "point cloud" datasets. Digital photography from 3 scanner-mounted cameras yields full dome panoramic images overlaid on highly accurate point clouds. The main coastal road in Palu was overwashed with flow velocities of more than 7 m/s. Field observations, drone videos, helicopter and satellite imagery are presented. Eyewitnesses interviewed based on established protocols indicate rapid tsunami arrivals within a few minutes of the earthquake. We educated residents about tsunami hazards as community-based education and awareness programs are essential to save lives in locales at risk from locally generated tsunamis. [ABSTRACT FROM AUTHOR]

The earthquake nucleation process is inherently complex, due to an involvement of several deformation mechanisms with multiple spatial and time scales. We here focus on a foreshock sequence which took place prior to a Mw 5.8 shallow crustal earthquake in 2013, at NE Japan. After relocating the foreshocks using travel time differential data constrained by waveform cross-correlation, we searched for events with similar waveforms to those of each relocated template event, applying a matched filter technique. Furthermore, we extracted one pair of repeating earthquakes from the reconstructed catalog (M>1.8), based on waveform similarity and nearly overlapping locations. The cumulative number of events showed an episodic increase toward the mainshock failure time. The initial crisis characterized as a tiny seismic cluster started from three weeks before the mainshock rupture. During about three days prior to the mainshock, a planer seismic cluster with ~0.5 km length had developed. Less than one hour just before the mainshock break, the foreshock activity abruptly became intensive and being concentrated along a eastward-steeply dipping fault plane (~0.5 km length) very close to the mainshock hypocenter. We recognize a distinct sequence of earthquake migration at an average speed of ~10 km/day over the fault plane along fault-dip and fault-strike, just after the largest foreshock (M3.6). Its migration front, slowing down with time, is well approximated by a parabolic curve and moved toward the rupture initiation point, which is analogous to the foreshock migration observed before the 2011 M9.0 Tohoku earthquake despite quite different spatial scales. Combining the foreshock migration with repeating earthquake, we suggest that slow slip transient propagated towards the nucleation point of the mainshock rupture. The partial unlocking of fault might take place episodically through interplay between fast and slow slip modes, prompting the subsequent unstable dynamic rupture. [ABSTRACT FROM AUTHOR]

Glacier-covered volcanoes are not only prone to explosive eruptions but can also generate huge subglacial floods. Interactions of the volcanoes' associated geothermal areas within the ice can also generate substantial subglacial floods. In Iceland, these floods can travel up to 50 km beneath the ice before they reach a glacial river, to subsequently flood the lowland and damage or destroy infrastructure such as large hydropower reservoirs and the only road circling the whole island. Hydrological instruments in the flooded river can provide up to 4-5 hours of early-warning for floods from W-Vatnajökull ice cap. During a flood in 2011 from Katla this early warning, however was only 50 minutes before the flood hit the main road. We present hydrological, GPS and seismic recordings of four floods in southeast Iceland. We show that in one specific flood the GPS instrument increased the early-warning time for floods to several days. Operation of these instruments on the ice surface however, can be sensitive to the harsh environment and costly. Therefore, to simultaneously monitor multiple subglacial lakes in a more reliable and less costly way, we suggest the use of seismic arrays situated outside the glacier margin. They are able to track the flood front at high temporal and spatial resolution and provide an early-warning for all four floods of more than 18 hours. [ABSTRACT FROM AUTHOR]

Only a decade ago, providing medium-size resolution tsunami propagation simulations in large domains was a computational challenge and wallclock times expanded up to many hours. At that time, thinking of using numerical models and on the fly computed solutions in the framework of TEWS was unthinkable. Then, and still today, decision matrices or, eventually, precomputed solutions are the tools used in these systems when response times are too short. In the other hand, building up huge precomputed tsunami scenario databases was a task that required many months of massive computing resources. The access to these resources was limited only to a few researchers and institutions.Nevertheless, in recent years a number of tsunami numerical models have been implemented to run in GPU and multi-GPU architectures, a topic in which our group has been pioneering. This technological approach has changed the rules of the game in TEWS and numerical models are at present day able to simulate a single event in just a few minutes and they have made it possible to achieve one of the main challenges in nowadays Tsunami Science: producing accurate assessments of the tsunami waves impact, mainly in populated areas, and just some minutes after the generating earthquake is triggered.In 2014, EDANYA Group was challenged by CAT-INGV at Rome. The challenge consisted in performing an 8h simulation in a 30 arc-sec resolution mesh of the whole Mediterranean Sea (10 million cells) in less than 6 min. This was achieved (in 352 sec) with a multi-GPU implementation of Tsunami-HySEA model using 10 nVIDIA Titan Black GPUs (2012 Kepler architecture). Then, in 2017, using only two Tesla P100 (2016 Pascal architecture) the same simulation was performed in 257 sec. The use of the newest Tesla V100 graphic cards (2018 Volta architecture, released 7 Dec 2017) further increased the speed-up, and the resources available at the BSC allowed us to used up to 64 Tesla V100 graphic cards for multi-GPU simulations. This allowed us to reduce computational times up to unthinkable limits. Limits that have moved the time required for this kind of simulations from hours, to few minutes and now to seconds. Through several examples, in the Mediterranean, Atlantic, Pacific and Caribbean, we explore the figures provided by Tsunami-HySEA model run in this cutting-edge computing technology. Where are the limits? or can we compute high-resolution inundation at a target area on the fly FTRT if sufficient computing resources are available? are questions that will we address to light of the figure presented.Acknowledgements. This research has been partially supported by the Spanish Government Research project SIMURISK (MTM2015-70490-C02-01-R), Universidad de Málaga, Campus de Excelencia Internacional Andalucía Tech and ChEESE project (EU Horizon 2020, grant agreement Nº 823844), https://cheese-coe.eu/ The numerical simulations were performed at Mare Nostrum 4 at Barcelona Supercomputing Center. [ABSTRACT FROM AUTHOR]

Seismic hazard assessment rests on the distance from the rupture zone to population centers, and on the magnitude estimation. The latter is controlled by the area ruptured along the fault plane and by the amount of slip accommodated during the earthquake. While progress has been made to estimate the ruptured area, the determination of how much slip occurs during an earthquake remains a major issue in improving hazard assessment. This is particularly true for thrust events, where traditional scaling relationships between seismic moment, area and slip fail, due to lack of understanding of the fault mechanical behavior close to the surface. Thrust faults are commonly known to produce larger slip, damage and ground acceleration as the rupture approaches the free surface. Preliminary work from Gabuchian et al. [2017] supports a novel solution which simply built on the natural asymmetry of the geometry of reverse faults. Combining numerical and experimental simulations, they showed that, when propagating up dip toward the free surface, the earthquake rupture induces large deformation, especially rotation of the hanging wall, the region above the fault.In this work, we take advantage of new numerical algorithms for dynamic modeling of earthquake rupture to describe more carefully the physical mechanisms behind the free surface effect. We use enhanced numerical algorithms for earthquake rupture recently developed by the Los Alamos National Laboratory. The numerical method behind these algorithms is called combined finite-discrete element method (FDEM) and can effectively reproduce earthquake rupture nucleation and propagation. It also captures the rich, and complex, deformation of the surrounding media, as it reproduces the dynamically activated off-fault fracture network. We first use this new numerical tool to better characterize rupture propagation on a dipping fault with dynamically-generated coseismic damage. Through a systematic analysis of case studies, we investigate the effect of the fault geometry, friction parameters and damage properties in the rupture evolution. We then use this numerical model to predict surface displacements and ground motions. These predictions will next serve as synthetic data when comparing with recorded surface deformation from past earthquakes. [ABSTRACT FROM AUTHOR]

Overtopping coastal defense walls of Oirase and Misawa with waves of 6-10 m, the 2011 Tohoku-oki tsunami caused massive damages along the entire coastline of Northern Japan. Along the shores of the Aomori Prefecture inundation reached up to 550 m inland, before stopped by the slope of a ca. 10-15 m high terrace scarp. Sandy tsunami deposits, however, only reach ~250-350 m inland. At the field site, a small fishing port, this clearly identifiable tsunami remains show up to 10 cm thick sand layers. Further observations show that the coastal forest stopped indicators of an inundation (such as barrels, fishing nets, buoys, etc.) within the first 50-75 m after entering the forest. Most larger objects were deposited in backwash positions whilst objects, such as fishing nets, remain on tree branches at run-up heights (up to 3.2 m) and are observable still 7 years following the event. Further inside the coastal forest the inundating tsunami waves eroded increasing amounts of the organic topsoil, including loose plant material and wood, which probably partially swam on top of the inundating water. Field observations show that this material is deposited by the 2011 Tohoku-oki tsunami as organic-rich peat-like sediments. Our observation shows that the organic- and plant-rich deposits first emerge on top of the clearly identifiable sand deposit as a thin layer. Then it thickens inland to up to 5 cm as the tsunami sands thin out. After ~250-350 m further inland no sands are preserved, but the organic- and plant-rich deposits. Along with the tsunami inundation a transported plastic particle (that swims) was deposited within this organic- and plant-rich tsunami deposit. As a conclusion, the 2011 Tohoku-oki tsunami serves as a blue-print for paleo-tsunami studies, as most of them only rely on sand deposits as marker for inundation distances from the beach, however the organic- and plant-rich layer reaches far more inland. The preservation/tracing and relics of this "lost" layer may contribute to (paleo-)tsunami hazard assessment in future. [ABSTRACT FROM AUTHOR]

On 14 November 2016, the Northern part of New Zealand's South Island was struck by the Mw7.8 Kaikōura earthquake, an event of unprecedented geometric complexity rupturing at least 21 segments of the contractional North Canterbury and of the Marlborough fault systems. Geological, geodetic, tsunami and seismic data reveal puzzling features as well as observational difficulties of the event leading to competing views on its key features, such as the role played by the Hikurangi subduction interface, the exact rupture sequence, and the higher than expected local tsunami. We present a dynamic rupture model of the 2016 Mw 7.8 Kaikōura earthquake to unravel the event's riddles in a physics-based manner and provide insights on the mechanical viability of competing hypotheses proposed to explain them. The event is modeled using the open-source software SeisSol (www.seissol.org), based on a arbitrary high-order accurate DERivative Discontinuous Galerkin method (ADER-DG). We verify our model with strong ground-motions, high rate GPS, long-period teleseismic and tsunami data. Our model reproduces key characteristics of the event and constraints puzzling features inferred from high-quality observations including a large gap separating surface rupture traces, the possibility of significant slip on the subduction interface, the non-rupture of the Hope fault, and slow apparent rupture speed. We show that a rupture cascade sequentially breaking the Papatea and Kekerengu faults is dynamically consistent with regional stress estimates and a crustal fault network geometry inferred from seismic and geodetic data. A coseismically triggered tsunami caused by the rare occurrence of an earthquake starting on-land and crossing to two faults off-shore matches local tide gauge data.We find, that such complex rupture cascade links the crustal fault system when operating at low apparent friction thanks to the combined effects of overpressurized fluids, low dynamic friction and stress concentrations induced by deep fault creep. Understanding the physical conditions that allow rupture cascades on complex fault systems advances our ability to quantify earthquake hazard, especially to evaluate the possibility of extreme events on real fault networks. [ABSTRACT FROM AUTHOR]

Effects of the Earth's rotation on tsunami wave dynamics has repeatedly been discussed in the literature. Usually it was concluded that these effects are minor. Such a conclusion is easily explained. It is known from geophysical hydrodynamics that the Earth's rotation effects are significant for processes for which the spatial scale is comparable with the barotropic Rossby deformation radius Ro (~2000 km) or exceeds it. Tsunami spatial scale Rts (~100 km) is determined by the size of co-seismic deformations area which is normally much inferior to the Rossby radius. There are exceptions to this rule: mega-earthquakes with moment magnitude Mw>9.0 and strong deep-focus earthquakes. In both cases co-seismic deformations cover extensive area which size can be comparable with the Rossby radius. The aim of this study is to reveal effects of the Earth's rotation on waves generated by two deep-focus seismic events: the Okhotsk Sea earthquake on May 24, 2013 (Mw=8.3, h=611 km) and the Fiji earthquake on August 19, 2018 (Mw=8.2, h=580 km). Being completely hazard-less due to a few centimeter amplitude, these unusually long tsunami-like waves are of great interest from the viewpoint of geophysical hydrodynamics. Our method is based on comparison of results of numerical experiments performed with and without the Coriolis force. It was shown that in case of the 2013 Okhotsk Sea event the Earth's rotation has a large effect on the spatial distribution of the maximum amplitudes and wave forms (Rts/Ro=1.4). In particular, taking into account the Coriolis force we obtain nearly twofold increase of wave amplitude in some bays of Okhotsk Sea. The observed differences are mostly caused by Kelvin waves, which exist only in a rotating ocean. For the 2018 Fiji earthquake the Earth's rotation effect, because of the proximity of the equator, turned out to be smaller (Rts/Ro=0.22). However, even in this case the Coriolis force noticeably alters the leading wave amplitude and tsunami wave-forms.AcknowledgementsThis work was supported by the Russian Foundation for Basic Research, projects 16-05-00053, 19-05-00351. [ABSTRACT FROM AUTHOR]

The region of Japanese island arc is one of the most seismically active regions of the world due to very high plate convergence rate. On March 11, 2011, the great Mw=9.0 Tohoku earthquake occurred in the central segment of the Japan subduction zone, the region where the previous megathrust earthquake was in 869. The duration of seismic cycle in this part of Japan subduction zone is estimated at about 800-1100 years. To identify the spatiotemporal variations of surface deformations following the 2011 earthquake we analyzed more than 12 years of continuous GPS observations from over 1400 stations of GEONET network that covers the entire territory of Japanese islands. Analysis of GPS data prior to Tohoku earthquake revealed a notable anomaly – a subsidence of coastal region directly opposite the future source zone of 2011 earthquake. This can be an evidence for the termination of elastic stresses accumulation and the transition of corresponding part of the seismogenic zone to the preseismic stage of the seismic cycle. Coseismic displacements captured by GPS stations allowed us to model the slip distribution in the earthquake source and to reveal significant effect of Fossa Magna Graben on the coseismic deformations pattern. Source zone of the Tohoku earthquake affected all possible seismogenic blocks, limited by geological bounds, such as Fossa Magna, which resulted in reestablishing of seismic cycle for the whole northeastern part of Japan subduction zone. The observed surface displacements before, during and after the Tohoku earthquake exhibited good agreement with the expected motions implied by the keyboard model of subduction zones [Lobkovsky et al., 1991] at the appropriate stages of the seismic cycle. At the same time, analysis of the displacement rate variations estimated over 1-year intervals after the Tohoku earthquake showed an intense ongoing postseismic motion of complex mechanism. We tested a hypothesis of significant afterslip in the earthquake source using 1-month cumulative displacements for the first half of the year after the earthquake. Our analysis of the afterslip process showed that its maximal contribution rapidly decreases in the first six months after the earthquake from 1-3 meters to 10-20 centimeters per month and cannot predict the observed long-term displacements. We also assessed the effect of coseismically-induced viscoelastic relaxation in the underlying asthenospheric wedge on observed surface deformations. Such a long-term postseismic process, which can last after megathrust earthquakes up to several decades can significantly affect the seismic cycle in the northeastern part of the Japan subduction zone, providing a probable explanation for seismic cycle prolongation. [ABSTRACT FROM AUTHOR]

The 2011 Tohoku-oki earthquake occurred in the well-studied Japan convergent margin andproduced coseismic and postseismic surface displacements well observed at several GPSsites, including a dense onshore network and offshore GPS-A stations. Such geodeticdata, particularly large landward postseismic displacements in the primary rupturearea, suggest that relocking occurred shortly after the earthquake. This has clearimplications for the slip deficit accummulation and thus the seismic hazard in theregion. However, the landward motion recorded at the sites closest to the trench issignificantly faster than the plate convergence rate, which suggests that it cannot beattributed solely to relocking. Instead, it has been explained through numericalmodelling as due to viscoelastic relaxations of the stresses induced by coseismicdisplacement. Numerical modelling is valuable as it can quantitatively connect the surface displacementfield to the relocking history of the megathrust interface as well as to the postseismicrelaxation history. We thus construct a finite-element model of the Japan subduction zonewith a simplified, spherical-shell 3D geometry. The model is driven to realistic preseismicstresses and strains by imposing the earthquake history of the last several decades. We thenuse it to investigate the geodetic signature of relocking history in the context of specificsubduction zone geometry and physical features. The hypothesis is that a combination ofrapid relocking and significant viscous relaxation is needed to explain the observedpostseismic surface velocities. The lithospheres in the model have linear elastic rheology, neglecting the minor anelasticcomponent of deformation, while the asthenospheres have Maxwell viscoelastic rheologies.The areas of the megathrusts modelled as non-seismogenic are also viscoelastic and thusallow for afterslip in response to stresses induced during coseismic slip. The lithosphericstructure is imported from the Slab2 dataset, derived from seismological data. The effect ofdifferent lithospheric thicknesses of both the overlying and downgoing plates is thenexplored. This accounts for uncertainties, heterogenity and the discrepancy between differentdefinitions of plate thickness. The spatial extent of the coseismically slipping patch in themegathrust is varied in different models, especially its updip limit. This is crucial inattempting to reproduce the surface displacement close to the trench. Furthermore, it reflectsuncertainties and possible variations in locking behaviour of peripheral areas of theinterface. Preliminary results show that rapid relocking is not sufficient to explain the landward anddownward displacements observed offshore on the upper plate. Work is ongoing to fullycharacterize the primary features of the subduction zone responsible for the observed surfacedisplacements. [ABSTRACT FROM AUTHOR]

Hydrophone hydroacoustic stations of the Comprehensive Nuclear-Test-Ban Treaty Organisation (CTBTO) International Monitoring System (IMS) comprise typically two triplets of water column hydrophones located in the axis of the Sound Fixing and Ranging (SOFAR) channel, which are deployed offshore to the North and South of an island. Triplet distances to the island vary from approximately 50 to 200 km, with each triplet connected to the on-shore receiving and communications equipment by fibre-optic submarine data cables. The systems relay underwater acoustic waveforms in the band up to 100 Hz in real time to Vienna via a shore based satellite link. One of these hydroacoustic stations, namely HA11, is on Wake Island (USA), an atoll in the western Pacific Ocean approximately 4,000 km west of Hawaii and 2,700 Km south-east of Japan.The current study examines the association between signals received at HA11 and known underwater natural events, i.e. earthquakes and submarine volcanic eruptions, near Ioto Island, Japan, formerly known as IwoJima. The underwater signals were detected at HA11 and localized based on cross-correlation of T-phases recorded at the hydrophones of the triplets. The hydrophones of each triplet are deployed in a triangular formation with approximately 2 km horizontal separation. A clear association is shown between water-borne signals from underwater eruptions received at HA11 and volcanic tremors recorded on Ioto Island by the in-situ seismic stations operated by the Japan Meteorological Agency. [ABSTRACT FROM AUTHOR]

The east coast of Tasmania is directly exposed to tsunamis originating from the Puysegur subduction zone, and would be affected approximately 90 minutes post-earthquake. Tasmania does not experience tsunamis frequently, and tsunami hazard is poorly understood and planned for in the state. Moreover, the risk to Hobart port operations from a large tsunami has not previously been considered. This study applied numerical modelling to simulate the effects of a maximum credible tsunami (Mw 8.7 earthquake of New Zealand's southwest coast, combined with a highest astronomical tide), with the aim of determining potential coastal inundation levels, and assessing risks to shipping operations in Hobart Port. Inundation modelling was performed using the ANUGA hydrodynamic library, together with a detailed terrain model constructed from LiDAR and bathymetric datasets. In addition, a dune erosion operator was written for ANUGA, to account for tsunami erosion of the sand dunes in front of affected areas. The maritime hazard assessment focused on tsunami impacts for shipping in the navigation channel and ports, including mobilisation and evacuation times required for specific vessel types that frequent the harbour. Modelling results show a maximum incoming tsunami wave of approximately 7 m in exposed coastal areas, which could lead to inundation depths of > 4 m in some places. Significant seiching and wave reflections are evident in Hobart's main channel and embayments, which would pose a considerable risk to marine craft. An important finding of this study is that the feasibility of shipping evacuation from Hobart port is questionable, given the timeframes involved and the nature of simulated water disturbance. This study demonstrates the use of numerical modelling to inform tsunami hazard assessment, and highlights an often overlooked aspect of tsunami hazard. Statewide emergency management plans are currently being updated to make use of this work. [ABSTRACT FROM AUTHOR]

On April 2014 the Iquique Mw 8.1 earthquake ruptured the interpolate contact between the oceanic Nazca and continental South American plates offshore northern Chile between 19.5°S to 21°S in April 2014. This earthquake did not fully release the strain accumulated since the last great megathrust (Mw 8.8) in 1877 and had left an unbroken segment in the south. From December 2014 to November 2016, we deployed an offshore network of 15 Ocean Bottom Seismometers (OBS) that covered the rupture area and the unbroken southern segment using the Chilean Navy ship OPV Toro and R/V Sonne. That data set is supplemented by five weeks of data from 67 OBS installed for a controlled source seismic experiment during cruise MGL1610 of the R/V Marcus Langseth in late 2016. Data acquired onshore by stations from of the IPOC (Integrated Plate Boundary Observatory Chile) and CSN (Chilean Seismological Service) networks are also included.We present first results of this ongoing project, which include double-difference hypocenter relocations based on waveform cross-correlation. Most of the seismicity occurs between 19.5 and 21°S up-dip of the patch of maximum coseismic slip during the 2014 earthquake, while the seismicity in seismogenic depths is highly concentrated forming well-defined clusters. The observed seismicity provides constraints on the structure of the marine forearc and enables us to relate the seismicity distribution to the background seismicity, seafloor morphology, and regional tectonics. [ABSTRACT FROM AUTHOR]

Northeast India is sandwiched between the seismically active plate boundaries of the Eastern Himalaya to the north and the Indo-Burman subduction zone to the east. This plate boundary system is different from the central Nepal Himalaya, due to oblique convergence across two orthogonal plate boundaries, resulting in a zone of distributed deformation both within and away from the plate boundary. Previous studies of spatial distribution and source mechanism of earthquakes have shown that the N20E convergence between India and Tibet is partitioned into N-S underthrusting and E-W subduction of the Indian plate beneath the Himalaya and Burma micro-plate, respectively. However, south-west of the plate boundaries, the middle-to-lower crust deforms by strike-slip faulting in the Kopilli Fault Zone (KFZ); upper-to-mid crustal strike-slip faulting along the western Brahmaputra Valley; and lower crustal strike-slip faulting beneath the Bengal Basin. Strike-slip faulting in the KFZ also extends northwards beneath the Eastern Himalaya and southeastward beneath the Naga fold-thrust belt. In order to understand the role of these strike-slip faults in accommodating the GPS derived convergence across northeast India, we study the source mechanism of recent earthquakes using teleseismic (for earthquakes with Mw>5) and local (4.0

A better characterization of seismic and aseismic slip behaviors of active faults is a crucial challenge for the seismic hazard estimation because it can influence the size and timing of large earthquakes. Geodetic and terrestrial measurements can provide a better picture of the fault slip budged and spatio-temporal evolution of creep mechanism. A number of studies based on Interferometric Synthetic-Aperture Radar (InSAR) and Global Positioning System (GPS) satellite observations until 2012 have found that the central segment of the August 17, 1999 Mw 7.4 Izmit earthquake on the North Anatolian Fault started slipping aseismically following the earthquake. In this study, we used new InSAR time series, obtained from TerraSAR-X and Sentinel 1A/B radar images acquired over the period 2011-2017, with near field GPS measurement campaigns performed every 6 months from 2014 to 2016. The mean velocity fields reveal that creep on the central segment of the 1999 Izmit fault rupture continues to decay, more than 19 years after the earthquake, in overall agreement with models of postseismic afterslip decaying logarithmically with time for a long period of time. Along the fault section that experienced supershear velocity rupture during the Izmit earthquake creep continues with a rate up to ~ 8 mm/yr. A significant transient accelerating creep is detected in December 2016 on the Sentinel-1 time series, near the maximum creep rate location, associated with a total surface slip of 10 mm released in one month only. Additional analyses of the vertical velocity fields show a persistent subsidence on the hanging wall block of the Golcuk normal fault that also ruptured during the Izmit earthquake. Our results demonstrate that afterslip processes along the North Anatolian Fault, east-southeast of Istanbul are more complex than previously proposed as they vary spatio-temporally along the fault. [ABSTRACT FROM AUTHOR]

Studying the mechanical response of the crust to large earthquakes provides unique insight into the processes of deformation in preparation for future earthquakes. Noise-based seismic velocity monitoring can directly probe the mechanical state of the crust at depth continuously in time. In this work, we study the deformation of the crust concerning the Mw 9.0, 2011 Tohoku-oki earthquake. In addition to the Hi-net short period sensors, we employ here for the first time for the noise-based monitoring the particular dense network of Hi-net tiltmeters as long period (8 – 50 s) seismometers to sample the crust below 5 km depth. Spatial distribution of strong velocity decreases at short periods can be limited to strong ground shaking induced by the 2011 Tohoku-oki earthquake, while the long period velocity changes correlate well with modeled static strain induced by viscoelastic relaxation and afterslip at depth. This observation indicates that the variations at depth are not a spurious effect of changes in the shallow layers. The amplitudes of coseismic velocity changes diminish with increasing depth. The temporal evolution of velocity changes at different depth shows that the maximum drops of velocity at greater depth are delayed in time with respect the date of the earthquake. This delay could find its origin in both the visco-elastic response of the crust to substantial strain changes or a complex response of crustal seismic velocities to transient deformation. [ABSTRACT FROM AUTHOR]

Earthquakes cluster in both space and time. Several studies claim that clustering properties may be controlled by the tectonic regime: as an example, a recent study finds that seismic sequences tend to last longer in extensional tectonic settings compared to the compressive ones. Such evidence is usually used to claim for a calibration of the short-term earthquake forecast models and of declustering models based on the tectonic environment under consideration.In this work, we investigate on the existence of possible differences in the earthquake clustering process in three areas related to distinct crustal tectonic regimes: Italy, Southern California and (onshore) Japan. Our approach avoids the arbitrary distinction among foreshocks, mainshocks and aftershocks and relies on a rigorous statistical analysis. Our results are compatible with the hypothesis of similar earthquake clustering properties in the three tectonic regions, superimposed to a background seismicity described by the Poisson process, whose rate may vary on short time periods. We conclude that, at least for active seismic crustal regions, the type of tectonic regime does not seem to play a key role in how seismic sequences evolve in the spatiotemporal domain. [ABSTRACT FROM AUTHOR]

We observed a shallow (H<10 km) seismic activity containing both low frequency events (LFE) and regular earthquakes using a dense local seismic observation network installed recently at northeastern Japan. Significant recurring activities of deep (H>20 km) LFE have been monitored carefully around several subduction zones including Japan. Additionally, activities of shallow and deep LFE are also reported worldwide occurring beneath several potentially damaging active volcanoes. Deep (H>15 km) LFEs have also been observed to occur in inland areas not associated with active volcanoes or volcanism.The shallow seismic activity we observed was located on the Tsugaru Channel, between the Hokkaido and Honshu Islands of Japan. We installed a local seismic network consisting of 36 stations, called AS-net, in 2013 and 2014 and are monitoring shallow and deep seismic activities in the region. AS-net improved both the earthquake detection capability and the accuracy of hypocenter determination around this region significantly. The shallow activity of earthquakes and LFEs was observed at just ~2 km south of an AS-net station. The seismic record at the station revealed that the depth of this seismic activity was shallower than 10 km. From 2014 to 2017, 23 earthquakes and 19 or more LFEs were detected. Both earthquakes and LFEs swarmed individually and intermittently. Magnitudes of all events were less than two. Both types of events seemed to occur in the vicinity of one and other however this is not clear because of the limit of the accuracy of the hypocenter location. At ~10 km eastward of this activity, we observed another activity of deep (15~35 km) LFEs in an area without volcanos. Above this curious shallow seismic activity, Yamagata et al. (1989) pointed out the existence of a volcano based on their research about tephra layers over Hokkaido. They estimated that a tephra layer on tens of thousands of years ago could be from Zenigame Caldera, a depression (1~2 km in diameter) at seafloor of Tsugaru Channel. Because it is under the sea, it is not easy to survey, and no other studies about this potential volcano have been reported.In Japan, opposite to deep LFEs, shallow LFEs are only monitored around potentially damaging volcanoes. Outside of such regions, the presence of shallow LFE is not clear. Shallow LFE activity and its mechanism as well as its relation to volcanoes should be clarified. By doing so, we will be able to locate potential volcanic activity by monitoring shallow LFEs; even underwater. Additionally, we have recently started to install several temporal seismic observation stations in the area surrounding this seismic activity to investigate it in detail. AcknowledgementsThe AS-net has been constructed and is being managed thanks to financial contributions by Tohoku Electric Power Co., Inc., Electric Power Development Co., Ltd., Japan Nuclear Fuel Limited and Recyclable-Fuel Storage Company. [ABSTRACT FROM AUTHOR]

Numerical simulations are conducted to examine the effect of heterogeneity of frictional property on earthquake cycles. Rate- and state-dependent friction is assumed on a planar fault in an infinite uniform elastic medium. One to four circular patches of steady-state velocity-weakening frictional property is assumed on the model fault plane, and velocity-strengthening friction is assumed outside the circular patches. Friction parameters are uniform within each patch, and the values of characteristic slip distance L in the patches are varied so that the effect of interaction between the patches with different frictional property may be examined. Simulation results indicate that simple periodic (period-1), multi-periodic (period-n, n > 1), and aperiodic earthquake cycles occur in the models. Here, a period-n cycle indicates that n different slip events are included in a cycle. In the one-patch model, simple periodic earthquake cycles occur for smaller L, where the critical nucleation radius h*, which is proportional to L, is smaller than the radius of the velocity-weakening patch, and multi-periodic and aperiodic sequences of slip events occur for larger L, where the patch radius is close to h* (Kato, 2014, Geophys. J. Int., 198, 727-736). In the two- to four-patch models, a patch is ruptured in some cases and some or all patches are simultaneously ruptured in the other cases. This causes complex earthquake cycles. Slip events of different combinations of patches occur. The possible number of combinations is larger for larger number of patches on a fault. Moreover, aseismic slip events occur within velocity-weakening patches with larger L, which also complicates sequences of slip events. Even in a velocity-weakening patch whose radius is smaller than h*, seismic slip may occur because it is triggered by seismic slip nucleated in another patch. In a parameter study where the characteristics of earthquake cycles are examined with a change in L in a patch, we find that earthquake cycles can be classified into several patterns according to the combination of ruptured patches in earthquakes. Complex aperiodic earthquake cycles tend to occur in a parameter range between parameter ranges of different patterns. Frequencies of multi-periodic and aperiodic earthquake cycles increase with the number of velocity-weakening patches, suggesting that more complex cycles may be generated in a fault with more heterogeneous frictional property. Frequency distribution of recurrence intervals of simulated earthquakes is discrete in the single-patch model and it becomes more continuous and realistic with an increase in the number of patches. These simulation results suggest that realistic complex earthquake cycles are caused by interaction among many patches of different frictional property. [ABSTRACT FROM AUTHOR]

Resonant oscillations (also known as seiches) in closed basins may be triggered by earthquakes and landslides and result in larger tsunamis amplitudes that in the open ocean. Moreover, seiches cause oscillatory currents at the seafloor that can influence sediment resuspension and deposition after earthquakes. In particular, processes generally invoked for turbidite-homogenite formation involve episodes of tractive transport under oscillatory currents (forming a laminated turbidite layer) followed by the settling of a cloud of suspended particulate matter (forming the homogenite). In the Sea of Marmara, numerical modeling had been performed in order to determine the periods of free oscillations modes (Yalciner and Pelinovsky, 2007) and the periods of the resonant oscillations typically fall in the range of infra-gravity waves, which suggests smaller amplitude ones may be triggered my meteorological events. In order to better constrain those models, an attempt to detect resonant oscillations and measure their frequencies and amplitudes was planned as part of MAREGAMI ANR-TUBITAK collaborative project and EMSO-France activities. A bottom pressure recorder and a doppler current meter are being deployed at successive locations in the Sea of Marmara for periods of about 6 months. We here present results of our first deployment session (February to August 2018) and re-examine data from an older record. Tidal oscillations with ≈12 hours and ≈24 hours dominant periods are observed with maximum amplitudes of 10 cm (10 hPa) crest to crest as well as 1-to-5-days intervals with higher frequency oscillations of centimeter amplitude. The frequency spectra of these oscillations display peaks at periods ca. 107, 78, 48.5, 41, 34.8, 24 and 22.4 minutes, only approximately matching results of numerical simulations. As in the numerical simulations, the spectra obtained vary with station location, which may be explained by local resonances, or if stations are located near the nodal lines of the missing modes. [ABSTRACT FROM AUTHOR]

We are studying the interaction between gases from the Earth (radon, methane, CO2) that may be associated with pre-seismic activities and the standard atmosphere in order to assess their potential thermodynamic impact. There is an increasing amount of observational evidence that the concentration of these gases increases before major earthquakes. We formulate a hypothesis that an increase in the concentration of these gases triggers a thermodynamic coupling between the lithosphere-atmosphere-ionosphere coupling (LAIC) and is linked to the seismic cycle. Therefore, by studying the LAIC processes we can detect variability in the Earth's gases, which allows us to make an inference about seismic activity. We use radon measurements on the ground installed and coordinated in five different seismically active regions: Southern California, Taiwan, Central Italy, Western Greece and South Eastern Japan. For this study we utilize both NASA and NOAA remote sensing data together with GPS/TEC observations. With Gold and Soter's initial hypothesis of the deep origin of radon and methane (1985), and the fact that the activation of faults leads to an increase in the emanation of gases, we are exploring the feasibility of detecting these gases by measuring their coupling impact on the Earth's atmosphere through ground and space observation. For this analysis we selected 8 large earthquakes from different seismo-tectonics regions: (1) M9.3, Sumatra, Dec 26, 2004; (2) M9.0 Tohoku, Japan, March 11, 2011; (3) and (4) M7.8 and M7.3 Gorkha, Nepal, 2015; (5); M8.2 Tehuantepec, Sept 8, 2017 and; (6) M7.1, Puebla, Mexico, Sept 19, 2017, (7) Mw 6.8 Zakynthos, Greece of Oct 25, 2018 (8) M6.6 Meinong, Taiwan, Feb 6, 2016,. We have found that: (i) radon and atmospheric anomalies have been observed before all of the analyzed events, (ii) large seismic events (M8+) could produce radon anomalies far from the epicenters; and (iii) long lasting seismic swarms could generate temporary elevation of radon levels in the near zone. We examined the possible correlation between magnitude and the spatial size of the earthquake preparation zone (Dobrovolsky- Bowman) in the framework of the LAIC concept. Our data analysis suggests that the pre-earthquake phase follows a general temporal-spatial evolution pattern; in which radon plays a critical role in understanding the LAIC involving different layers of the ionosphere, atmosphere and lithosphere. Pre-Earthquake Processes: A Multi-disciplinary Approach to Earthquake Prediction Studies, AGU/Wiley, 2018, 385 pp, (Ed's: Ouzounov D., S. Pulinets, K.Hattori, P.Taylor) The Possibility of Earthquake Forecasting: Learning from nature, Institute of Physics Books, IOP Publishing, Dec 2018, 168pp (S. Pulinets and D. Ouzounov) [ABSTRACT FROM AUTHOR]

We present an interdisciplinary study of observations of pre-earthquake processes associated with major earthquakes based on integrating space and ground observations. Recent large magnitude earthquakes in Asia, Europe and Americas have emphasized the various observations of multiple types of pre-earthquake signals recorded either on the ground or from space. We are studying the general temporal-spatial and evolution patterns of these pre-earthquake signals and their significance as a function of retrospective and prospective testing. We formulate a concept that an increase in the concentration of geo gases (radon, methane, CO2) triggered a lithosphere-atmosphere-ionosphere coupling (LAIC) and is linked to the seismic cycle. Therefore, by studying the LAIC processes we can detect transitional coupling in geospheres, which allows us to make an inference about seismic activity. The Multi Sensor Networking Analysis (MSNA) is our method for validation and is based on a joint analysis of several physical parameters: Satellite transient infrared radiation anomalies (STIR), electron concentration in the ionosphere (GPS/TEC), geogas/radon activities, air temperature/humidity patterns, that were found to be associated with earthquakes. The MSNA is based on multi-disciplinary approach, because it is widely recognized that our understanding of geophysical processes is improved by integration of studies from seismology, geochemistry, geomagnetism, atmospheric science and geology. To quantify our validation, we start computing Molchan Error Diagram (MED) retrospectively and prospectively for anomalous ionospheric/atmospheric signals. Our validation processes included retrospective analysis since 2004 of major earthquakes preformed over the regions with high seismicity- Taiwan, Japan, China California, Mediterranean, Mexico, Chile and Kamchatka and prospective testing for potential for M7+ events since 2013 worldwide and a special test for M6+ over the Japanese region. Still an average false alarm ratio of 25% exists, but the method has the potential for improvements, with more research. Our results suggest that: (1) Pre-earthquake atmospheric/ionospheric signals follow the LAIC proposed temporal-spatial evolution pattern (with 1-30 days' time-lag), which has been seen for most of large earthquakes worldwide; (2) Testing of pre-earthquake signals shell continue moving from single towards multi-parameter testing; and (3) MED test results indicate that pre-earthquake atmospheric anomalies could provide short-term predictive information in the tested regions. A detail summary of this approach been published in AGU/Wiley and Institute of Physics monograph series.Pre-Earthquake Processes: A Multi-disciplinary Approach to Earthquake Prediction Studies, AGU/Wiley, 2018, 385 pp, (Ed's: Ouzounov D., S. Pulinets, K.Hattori, P.Taylor) The Possibility of Earthquake Forecasting: Learning from nature, Institute of Physics Books, IOP Publishing, Dec 2018, 168pp (S. Pulinets and D. Ouzounov) [ABSTRACT FROM AUTHOR]

Continuous records of low-frequency seismic noise on the Japanese islands have been available since the beginning of 1997 at stations of the F-net broadband network. Their analysis allows us to test a number of hypotheses about how the preparation of strong earthquakes affects the statistical properties of noise, as well as about the possibilities of using changes in the properties of noise to search for precursors of strong seismic events [1]. The temporal evolution of the average values of the properties of seismic noise from the entire network and from its various parts when they are estimated in a sliding time window demonstrate a number of features, the explanation of which requires the involvement of information about planetary causes that can serve as a source of modulations. In the report, it is proposed to consider the irregularity of the Earth's rotation, the data of which has been available since 1962 - the length of day (LOD) time series. Estimates of quadratic coherence between LOD increments and daily medians of seismic noise properties in an annual sliding time window are presented. The maxima of such coherence are concentrated in a narrow frequency band with periods ranging from 11 to 14 days, with a surge of maximum coherence in 2003, which was previously detected for global seismic noise [2]. These properties of seismic noise coupling with LOD are retained for the F-net regional seismic network in Japan, but a number of features appear associated with the preparation of the Tohoku seismic disaster on March 11, 2011 (M = 9.1). In particular, after the previous strong earthquake off the coast of Hokkaido on September 25, 2003 (M = 8.3), variations in the coherence spectrum showed periodicity with a period of about 2 years, which after the Tohoku event changed to a monotonous growing trend. The possibilities of using these features for the purposes of estimating seismic hazard trends are discussed.The work was supported by Russian Foundation for Basic Research (project no. 18-05-00133).Reference1. Lyubushin A. Synchronization of Geophysical Fields Fluctuations // Tamaz Chelidze, Luciano Telesca, Filippos Vallianatos (eds.), Complexity of Seismic Time Series: Measurement and Applications, Elsevier 2018, Amsterdam, Oxford, Cambridge. Chapter 6. P.161-197. https://doi.org/10.1016/B978-0-12-813138-1.00006-7 2. Lyubushin A. (2018) Global Seismic Noise Synchronization and Seismic Danger Increasing in Connection to Irregularity of Earth's Rotation – 36th General Assembly of the European Seismological Commission, 2-7 September 2018, Valleta - Malta. Session S16: Advances in models, observations and verification towards operational earthquake forecasting. The book of abstracts of the ESC2018 General Assembly, ISBN: 978-88-98161-12-6, abstract ESC2018-S16-54, https://doi.org/10.13140/RG.2.2.28107.64800 [ABSTRACT FROM AUTHOR]

Solar-induced geomagnetic disturbances of the Earth's Magnetic Field (EMF) are well characterized by two geomagnetic indices, Kp and Dst. The 3-hour index Kp (Bartels, 1949) has been available from 1932 onwards, the hourly Dst index since 1957 as published by ISGI, the International Service of Geomagnetic Indices, France. Both indices are closely linked to the solar flare activity and the solar wind speed, as recorded near-Earth by spacecraft data as provided by OMNIWeb (NASA). In our study, Dst is taken as an indicator for the degree of geomagnetic disturbances of the entire globe, derived from data by four low latitude magnetic observatories, selected by IAGA. Dst describes the disturbances of the horizontal component H of the EMF, symmetrical to the Earth geomagnetic dipole axis. Thus, Dst can be considered the 'zonal part' of the disturbed field (IAGA Bull. 27,1969). Geomagnetic storms cause a decrease in the horizontal component H due to the magnetospheric ring currents generated by solar particle radiation. These ring currents generate a magnetic dipole field which counteracts the Earth's dipole and causes the depression of H. While the main phase of geomagnetic disturbances typically lasts many hours, it generally takes several days for the intensity of H to return to normal values.Early studies (Duma,Vilardo,1998; Duma,Ruzhin,2002) demonstrated already that seismic activity in numerous earthquake zones exhibits systematic diurnal variations which can only be attributed to a solar influence via the ionospheric electric current vortices, by induction of telluric currents in the Earth's lithosphere. Seismic activity follows the trend of the magnetic solar quiet-day variation Sq, in Local Time. Similar results were obtained in the seasonal range and even in the range of about 11 years, the sunspot cycle. The results of the present study indicate that an overwhelming majority of earthquakes M bigger 7 happen within a time window of some ± 10 days around Dst minima. Of all events M bigger 7 in the period 2010-01 to 2018-02 in the Northern hemisphere, i.e. a total of 30 events according to the USGS Earthquake Catalogue, more than 90 % occurred in that time window, in particular the Tohoku (2011, M9.1) and Kumamoto (2016, M7.0) earthquakes in Japan as well as the weaker events in Italy such as L'Aquila (2009, M6.3) and Norcia (2016-08-24, M6.2; 2016-10-30, M6.6).The effect had already been clearly identified in a previous study by us for earthquakes such as Haicheng (1975, M7.0), Tangshan (1976, M7.5), Loma Prieta (1989, M6.9), Kobe (1995, M7.3), Taiwan (1999, M7.7). Statistical results and their significance are presented, strongly confirming the solar trigger action for major earthquakes. A model of the geodynamic action, which would quantify the interaction of the main Earth's magnetic dipole field and the solar-induced counter dipole is not yet available. [ABSTRACT FROM AUTHOR]

Phenomena preceding the M9 Tohoku earthquake in Japan on 11 March 2011 and the M8.2 Mexico earthquake on 7 September 2017 have been explored by analyzing the seismic data in natural time. Interesting results have been obtained for the following quantities that have been studied very recently [1-4]: First, the entropy change under time reversal [1,2]. Second, the complexity measure quantifying the fluctuations of the entropy change under time reversal [3,4]. Third, the fluctuations of the order parameter of seismicity.References:1. N. V. Sarlis, E. S. Skordas P. A. Varotsos, A. Ramírez-Rojas, E. L. Flores-Márquez, "Natural time analysis: On the deadly Mexico M8.2 earthquake on 7 September 2017", Physica A 506 (2018), 625-634.2. N. V. Sarlis, E. S. Skordas, and P. A. Varotsos, "A remarkable change of the entropy of seismicity in natural time under time reversal before the super-giant M9 Tohoku earthquake on 11 March 2011", Europhysics Letters (EPL), 124 (2018), 29001.3. A. Ramírez-Rojas, E. L. Flores-Márquez, N. V. Sarlis and P. A. Varotsos, "The Complexity Measures Associated with the Fluctuations of the Entropy in Natural Time before the Deadly México M8.2 Earthquake on 7 September 2017", Entropy 20 (2018), 477.4. P. A. Varotsos, N. V. Sarlis and E. S. Skordas, "Tsallis Entropy Index q and the Complexity Measure of Seismicity in Natural Time under Time Reversal before the M9 Tohoku Earthquake in 2011", Entropy 20 (2018), 757. [ABSTRACT FROM AUTHOR]

Plate tectonics is a recent scientific concept compared to the history of science. The knowledge of the scientific techniques of investigation is fundamental to understand the current vision of the functioning of the Earth. Human has always been based on observations to construct his representations of his environment. The evolution of the techniques gradually made it possible to move from a static flat Earth model to a more dynamic spherical model.14 year-old students are interested in science but for many of them, only knowledge is important. However, the link between scientific investigation and knowledge is not to be neglected. This allows us to understand that science is not a fixed discipline: the models of planet Earth have evolved enormously and may still change with technological evolution.To make the discovery of the subduction phenomenon more attractive and more ingrained in the current era, students will use a website that collects and shares seismological data. This site, which provides three-dimensional earthquake distribution images, is updated daily, allowing students to link to current events: IRIS (Incorporated Research Institutions for Seismology; http://ds.iris.edu/seismon).The starting problem proposed to students is explain why Japan is so often affected by earthquakes (1 / 5th earthquakes with a magnitude equal to or greater than 6 recorded in the world occur in Japan).Students have at their disposal:- A technical sheet allowing them to quickly take in hand the tools proposed by the site- A review of knowledge on the physical properties of the lithosphere and the asthenosphereStudents have to produce:- A text proposing an explanation to the recurrent geological phenomena observed in Japan (use of imposed vocabulary words: lithospheric plate, asthenosphere, earthquake).- A legendary dynamic scheme based on the interpretation of the three-dimensional images generated by the website.Once the time is up, one of the groups presents their work to the class and the word "subduction" is finally given to the students. [ABSTRACT FROM AUTHOR]

Okal et al. (2014) developed an algorithm, named TS formula, to estimate teleseismic tsunami amplitudes from the seismic moment of the parent earthquake, the azimuth between its fault strike and the receiver, and the epicentral distance; this method was based on least-square regressions over a large data set of numerical simulations (4650), using 10 source regions located in the main subduction zones of the Pacific Basin, and a range of four orders of magnitudes of seismic moment. We apply the inverse methodology to recover the seismic moment of historical earthquakes from their tsunami amplitudes. Inversion of the TS formula to recover the seismic moment was first tested on a set of real tsunami amplitudes, recorded in deep ocean basins by the DART buoy network (see http://www.ndbc.noaa.gov/dart.shtml). The tests were conducted on more than 250 measurements from 20 sources, and reproduced estimates of the seismic moment with an average precision of 0.22 logarithmic units. We point out that this method, which is independent of direct seismic measurements, provides the possibility to highlight non regular earthquakes like 'snappy' or 'slow' ones, and large unusual 'compact' sources like the 2011 Tohoku event. This methodology was then applied to historical events using a data set of 52 earthquakes and tsunamis, between 1854 and 2010, at 164 tide-gauge stations. For this study, the concept of deep sea measurement of tsunami amplitudes has been extended to amplitudes recorded by coastal sea-level stations (tide gauges), using a transfer function based on Green's law, which gives an estimation of the tsunami amplitude near the shore as a function of the deep sea measurements (see Reymond et al. (2011) and Jamelot & Reymond (2015)) and conversely. In this framework, we were able to reassess the seismic moment of some remarkable historical events including Peru-Chile 1868 and 1877, Ecuador 1906, Samoa 1917, Kermadec 1917, Tonga 1919, Chile 1922 and 1960, Alaska 1964..etc. The case of the tsunami earthquakes (Aleutian 1946, Nicaragua 1992, Java 1994 and 2006, Sumatra 2004, etc.) has been also considered.References:Okal, E.A., D. Reymond, and H. Hébert, From earthquake size to far-field tsunami amplitude: Development of a simple formula and application to DART buoy data, Geophys. J. Intl.,196, 340-356, 2014.Reymond, D., E.A. Okal, H. Hébert, and M. Bourdet, Rapid forecast of tsunami wave heights from a database of pre-computed simulations, and application during the 2011 Tohoku tsunami in French Polynesia, Geophys. Res. Letts., 39, (11), L11603, 6 pp., 2012.Jamelot, A., & Reymond, D.. New tsunami forecast tools for the French Polynesia tsunami warning system Part II: numerical modelling and tsunami height estimation. Pure and Applied Geophysics, 172(3-4), 805-819, 2015. [ABSTRACT FROM AUTHOR]

The promotion of earthquake research in Japan covers comprehensive basic policies for thepromotion of seismic research through the observation, measurement and survey ofearthquakes. HERP (Headquarter for Earthquake Research Promotion) proposed a frameworkof survey and observation plan of earthquakes in Japan. At the first stage of this framework, itconsists of observation of crustal activities and surveying of underground structures. Nextstep is to improve the methods of predicting strong ground motion and increase accuracy,and thus the improvement of seismic hazard maps. In order to fully capture theseismic hazard of a region, we must understand the effects of the regional 2D/3Dunderground structure on wave propagation. Selection and modification of groundmotion time series to represent a specific hazard at a site has a large impact on theresults of nonlinear response history analyses using these input motions, indicatingthe need to establish rational procedures for ground motion selection, scaling andmodification. Validated seismological methods may be used to generate ground motiontime series that incorporate near-fault rupture directivity effects and basin effects,and appropriately represent the duration and long period energy content of theselarge design events. These effects cannot be fully predicted by simply adoptingGMPEs that are developed for other regions. The main objective of this project is todetermine time-histories for distant and near-field earthquakes through ground motionsimulations. This joint project proposes to investigate the validation of the modeling procedure ofdetermination of geological models proposed by HERP for seismic hazard map in Japan, andoutput of this validation will be applied to the Eskisehir basin in Turkey. We canunderstand the performance of the procedure through the application to the Kumamotoarea by the Japanese side (using HERP procedure), and will be compared with theresults from Eskisehir by Turkish side. We also incorporate the methods used in theJapanese procedure into estimation of geological models in the Eskisehir basin. Inthis frame, we attempt to calculate broadband period ground motion time seriesfrom near-field and far-field earthquakes by using source modeling and groundmotion techniques. The effects of ground motions having a broadband period rangecan be studied in two parts; first one is the rupture directivity effects and secondlybasin edge effects. The prediction and simulation of such ground motions needsource modeling, determination of 2D/3D basin geometry and S-wave velocitystructure. We performed both array- and single-station microtremor measurements at a number oflocations so as to characterize the area to determine 1-D S-wave velocity structures down tothe bedrock depth beneath the strong motion sites for the broadband simulation. Finalgeological models obtained will be verified by seismic interferometry method andmicrogravity measurements. As next step, we make ground-motion simulations to get timehistories to analyze the effects of ground motions to buildings. In spite of increasing numberof buildings having different heights and characteristics in urbanized areas in Turkey, a fewstudies exist on the interaction of such buildings with ground motions having broadbandperiods. [ABSTRACT FROM AUTHOR]

The moment released by postseismic deformation of a large earthquake is typically smaller than its coseismic rupture, which the coseismic rupture should have released the main portion of the accumulated strain. However, it is not uncommon that the accumulative postseismic displacement is larger than or equal to the coseismic displacement based on geodetic observations on some subduction zone environments. The rational cause of such a large postseismic deformation may require a weakly coupled interface near the source rupture to allow prolonged large postseismic slip. Nevertheless, both the coseismic and postseismic deformation of subduction zone earthquakes are mostly derived from inversion of inland geodetic observations, yet the ruptures often occurred at the interface located mostly offshore, which resulted in poor resolution on the slip distribution model. Thus, whether unusually large postseismic deformation may occur on certain subduction zone earthquakes, and if so, what is the main cause of the large postseismic slip require further investigations on earthquakes with such an attribute. The 2016 Mw 6.5 Meinong earthquake occurred beneath the fold-and-thrust belt in SW Taiwan. Based on GPS observations, the two-years accumulated postseismic moment (Mw = 6.60) is larger than the coseismic moment (Mw = 6.43) of the 2016 Meinong earthquake, which renders a paradigm for large postseismic deformation of an earthquake occurred beneath a frontal thrust wedge. We consider that the large postseismic deformation of the 2016 Meinong earthquake is likely activated by slip on the high pore-pressure detachment on the frontal thrust wedge. On the detachment the high pore-pressure fluid overlapped with ~5-km thick sediments, diffused slowly and caused prolonged postseismic deformation observed in SW Taiwan. Some unusually large postseismic deformation are likely caused by activations of localized high pore-pressure mud diapirism, including the one located above the coseismic rupture. [ABSTRACT FROM AUTHOR]

The rupture-zone averaged static stress drop in the 2011 M=9 Tohoku-oki earthquake wasless than 5 MPa according to all published slip models, but it caused a reversal of the state ofstress in most of the offshore forearc, from predominantly compressive to predominantlyextensional. In this work, we demonstrate that this stress reversal has the followingimportant geodynamic implications. (1) The reversal unequivocally indicates avery weak subduction megathrust. In order to reproduce this reversal in a finiteelement model of force balance that quantifies the effects of gravity and megathrustfriction, the effective coefficient of friction of the megathrust has to be about 0.032. Alower value would make the forearc too extensional before the earthquake, and ahigher value would make it too compressive after the earthquake. (2) The very weakmegathrust results in very low differential stresses in the upper plate, consistent withpreviously reported sensitivity of the state of stress to small perturbations. Applying thedynamic Coulomb wedge model, we demonstrate that the inner wedge, and byinference the nearshore-onshore forearc, is in a stable state throughout subductionearthquake cycles, far from failure. (3) The outer wedge is normally in a stable state butmay reach an extensionally or compressively critical state during an earthquake,depending on the behavior of the shallow megathrust. Gravitational collapse of theouter wedge is prevented by a finite strength of the underlying shallow megathrust.Therefore, complete stress drop (i.e., effective coefficient of friction decreases tozero) is unlikely to have happened over the main part of the shallow megathrustexcept for limited local areas. (4) The presence of permanent deformation such asearthquakes and active faulting in the overall stable forearc can be explained bystructural and stress heterogeneities. We propose that for the most part, the upper platenear a subduction zone is much below its yield stress and is an elastic body, butpermanent deformation can locally occur in areas of low strength, high stress, orhigh fluid pressure. (5) The concept of dynamic Coulomb wedge (Wang and Hu,2006, JGR) needs to be expanded to address timescales much beyond subductionearthquake cycles. The strength of the megathrust varies over geological timescales,affecting the stability of the outer wedge and its response to earthquake rupture. [ABSTRACT FROM AUTHOR]

Mountainous areas are quite sensitive to global-scale environmental changes, such as warming. Therefore, the effect of global warming on these meteorological elements is a critical issue. However, Mt. Fuji Weather Station, which was once a symbol of meteorological observation in mountainous areas in Japan, has remained unmanned since August 2004. Of the other observation sites of the Japan Meteorological Agency, Nobeyama, at 1350 m.a.s.l. elevation, is the highest. When evaluating the effects of a global-scale warming event on regional-scale environmental change in the Japanese Alps at a high elevation of 1350 m.a.s.l., it must be noted that the lack of meteorological observation data at high elevations impedes any evaluations of the effects of warming on the ecological system and water resources in mountainous ranges. A network of 14 meteorological observatories has been developed by Shinshu University in the Japanese Alps, which have already started recording observations. The highest observation site is Mt. Yari, at 3125 m.a.s.l.. Observation data from these sites are sent to a computer at the laboratory via a data communication mobile telephone network or a phone line throughout the year. These meteorological observation data are available on the laboratory website in quasi-real time. The interannual variability of annual mean air temperature and snow depth in the Japanese Alps region are discussed. [ABSTRACT FROM AUTHOR]

In the latest decade new and more complex physics-based simulators have been developed and have acquired a growing interest as a tool for the comprehension and testing of seismic process models.Here we introduce a new generation earthquake simulation algorithm and its potentiality for modelling both short- and long-term spatiotemporal process of strong earthquakes preparation. A specific seismogenic structure is modelled by quadrilateral faults constituted by thousands of cells of few kilometres size each. The physical model on which the latest version of our simulation algorithm is based includes, besides tectonic stress loading and static stress transfer as in the previous versions, also the Rate & State constitutive law. The simulator code can be run on a relatively modest computer and is capable of simulating thousands years of seismic activity producing catalogs of tens of thousands events in a wide range of magnitudes. The resulting synthetic catalogs exhibit typical magnitude, space and time features, which are comparable with those of real observations.In this study we applied the simulator code to a physical model of the Nankai mega trust, a well-known seismic structure 650 km long, aligned with the Pacific Ocean coast of Southern Japan, which generated several earthquakes of magnitude larger than 8.0 in the last few centuries. This structure is typically modelled as subdivided in five main segments characterized by different slip-rates, which can rupture separately from or simultaneously with each other.The results of this simulation provide interesting inferences on the spatiotemporal properties of seismic activity in the study area. In particular, the recurrence time of large events and their spatial relation, can be studied. As the simulator algorithm allows displaying the stress pattern on all the cells constituting the seismic structure, in this study we have focused our attention on the time evolution of such stress before, during and after large earthquakes. In particular, we have quantitatively recognized that the ratio between the average stress and its standard deviation on the cells constituting a specific fault segment always increases with accelerating rate before a large rupture on a part or all of such segment, or even several joint segments. [ABSTRACT FROM AUTHOR]