Search

To estimate the connectivity of a road network, it is crucial to evaluate the correlation of hazard intensities among individual bridge locations since the probability of multiple bridges being damaged simultaneously depends on the degree of this correlation. However, research on connectivity assessment of bridge networks considering spatial correlations associated with flood intensities is scarce in the literature. When quantifying the spatial correlation of flood intensities, modeling based on the stream distance rather than the Euclidean distance is required, taking into account that river flow is restricted only within the stream network. To achieve this purpose, a novel methodology is proposed to evaluate the spatial correlation of a stream network based on a geostatistical linear model and stream network covariance models. In addition, this study considers the spatial correlation of seismic hazard intensity. With the proposed method, it is possible to identify which bridges play an important role in ensuring the connectivity of the road network under multiple hazards, i.e. flood and seismic. As an illustrative example, the proposed method is applied to a hypothetical bridge network in Kumamoto Prefecture, Japan. The results demonstrate that improved network connectivity can be achieved by implementing a relevant retrofitting strategy for important bridges. [ABSTRACT FROM AUTHOR]

A devastating earthquake with moment magnitude 7.5 occurred in the Noto Peninsula in central Japan on 1 January 2024. We estimate the rupture evolution of this earthquake from teleseismic P‐wave data using the potency‐density tensor inversion method, which provides information on the spatiotemporal slip distribution including fault orientations. The results show a long and quiet initial rupture phase that overlaps with regions of preceding earthquake swarms and associated aseismic deformation. The following three major rupture episodes evolve on segmented, differently oriented faults bounded by the initial rupture region. The irregular initial rupture process followed by the multi‐scale rupture growth is considered to be controlled by the preceding seismic and aseismic processes and the geometric complexity of the fault system. Such a discrete rupture scenario, including the triggering of an isolated fault rupture, adds critical inputs on the assessment of strong ground motion and associated damages for future earthquakes. Plain Language Summary: On 1 January 2024, a moment magnitude 7.5 earthquake occurred in the northern Noto Peninsula, Japan. The strong ground motion and tsunami associated with the earthquake caused severe damage to buildings and infrastructure, resulting in at least 245 causalities in the affected areas. The Noto Peninsula is affected by northwest‐southeast compression, and active reverse faults are known along the northern coast of the peninsula and its offshore region. Before the 2024 earthquake, the source region experienced long‐lasting earthquake swarm activity, which is a set of seismic events without an obvious mainshock‐aftershock pattern. Our seismological analysis found that there was a 10‐s‐long initial rupture episode around the hypocenter that overlapped with the earthquake swarm region. The initial rupture was followed by a series of three different rupture episodes on differently oriented fault segments. This earthquake highlights a multi‐scale rupture growth across a segmented fault network after a very quiet initial rupture process that was controlled by the preceding earthquake swarms and associated aseismic deformation related to fluid injection from depth. The rupture process advances our understanding of earthquake source physics and can lead to a better assessment of future earthquake hazards. Key Points: The 2024 Mw 7.5 Noto Peninsula earthquake involves a multi‐segmented rupture sequence on differently oriented faultsThe long and quiet initial rupture domain coincides with the preceding earthquake swarm regionFluid‐induced earthquake swarms and a segmented fault network control the complex earthquake rupture growth [ABSTRACT FROM AUTHOR]

This study is devoted to application of some new statistical methods to analysis of the spatial structure of the seismic field in a seismically active region in the neighborhood of Japan bounded by the following coordinates: 28°–50° north latitude, 130°–150° east longitude. The estimates of the seismic flux were obtained by using the k-nearest neighbors method for the magnitude interval m ≥ 5.2. The highest values of seismic flux intensity of about 10–4 are located at depths of down to 100 km and manifest themselves in the neighborhood of the Tohoku megathrust earthquake. The spatial resolution of the intensity estimates is ranging from 33–50 km in the regions with a high intensity to 100 km and larger in the zones with a weak intensity. It has been shown that the seismic filed parameters—intensity λ, slope of the magnitude–frequency graph β, maximum possible magnitude m1—have different scales of their spatial variability and, thus, it is necessary to apply different scales of spatial averaging to them. Based on the Gutenberg—Richter truncated distribution model, the estimates are obtained for the slope of the magnitude–frequency graph (b‑value) and the upper boundary of the distribution m1. An original method is proposed for determining the optimal averaging radius for an arbitrary cell of the space grid. The method is based on the use of the statistical coefficient of variation of the corresponding parameter. For the considered region, the estimate of the maximum possible magnitude Мmax= 9.60 0.41 was obtained with consideration of the correction for bias. [ABSTRACT FROM AUTHOR]

Landscapes disturbed by shallow landslides present several residual risks. For example, residual soils on sliding surfaces may lead to the re-occurrence of shallow landslides, and landslide deposits on valley floors may introduce multiple hazards associated with river blocking or landslide damming. Despite such risks, few studies have investigated the residual risks following shallow landslides, and thus, no methodology has been established for assessing such risks. In this study, we combined portable cone penetration test (PCPT) and electrical resistivity tomography (ERT) to investigate the post-event risks associated with a landslide scar resulting from the 2018 Hokkaido Eastern Iburi earthquake (HEIE) in Japan. The multi-point PCPT identified the interface between a weak volcanic soil layer and underlying weathered sedimentary rocks. This interface exhibited an abrupt spatial change in resistivity, ranging from 20 to 100 Ωm. The thickness of the residual soil layer was 0.3–3.2 m and that of the landslide deposit exceeded 2.0 m. An infinite-slope stability analysis was performed to predict the re-occurrence of shallow landslides due to a lower intensity earthquake than that of HEIE in this region. Considering the area affected by the HEIE and the physical properties of soil layers, our findings imply a widespread risk of re-occurrence of shallow landslides over an area of 20 km × 20 km. Although the areal coverage of the combined ERT/PCPT method needs to be extended, it is effective for assessing the residual risks associated with shallow landslides. [ABSTRACT FROM AUTHOR]

This paper presents a rapid or real-time estimation method of the economic value of direct stock damages caused by significant earthquakes in Japan. The result will contribute to both the government and private sectors' early decision-making, particularly for provisional budget allocation. First, we developed a simple but evidence-based model for estimating stock losses explained by a representative earthquake hazard factor and an exposure factor, i.e., seismic intensity and existing stock of physical assets. The key characteristic of our estimation model is that the dependent variable is prefectural damage amount. Still, the explanatory variables come from municipal sources: we overcome this data availability problem through our estimation process. Second, we carefully checked the model's specification, estimation, and performance to be soundly applied to a real-time assessment of future earthquake events. We also explain the automated measuring of the prefectural direct loss value and its distribution to every 250 m mesh. Finally, we show two examples of the application of our model; one is the case of the 2018 Northern Osaka Earthquake, and the other is the anticipated Tokyo inland earthquake. [ABSTRACT FROM AUTHOR]

Slow earthquakes are episodic slow fault slips. They form a fundamental component of interplate deformation processes, along with fast, regular earthquakes. Recent seismological and geodetic observations have revealed detailed slow earthquake activity along the Japan Trench—the subduction zone where the March 11, 2011, moment magnitude (Mw) 9.0 Tohoku-Oki earthquake occurred. In this paper, we review observational, experimental, and simulation studies on slow earthquakes along the Japan Trench and their research history. By compiling the observations of slow earthquakes (e.g., tectonic tremors, very-low-frequency earthquakes, and slow slip events) and related fault slip phenomena (e.g., small repeating earthquakes, earthquake swarms, and foreshocks of large interplate earthquakes), we present an integrated slow earthquake distribution along the Japan Trench. Slow and megathrust earthquakes are spatially complementary in distribution, and slow earthquakes sometimes trigger fast earthquakes in their vicinities. An approximately 200-km-long along-strike gap of seismic slow earthquakes (i.e., tectonic tremors and very-low-frequency earthquakes) corresponds with the huge interplate locked zone of the central Japan Trench. The Mw 9.0 Tohoku-Oki earthquake ruptured this locked zone, but the rupture terminated without propagating deep into the slow-earthquake-genic regions in the northern and southern Japan Trench. Slow earthquakes are involved in both the rupture initiation and termination processes of megathrust earthquakes in the Japan Trench. We then compared the integrated slow earthquake distribution with the crustal structure of the Japan Trench (e.g., interplate sedimentary units, subducting seamounts, petit-spot volcanoes, horst and graben structures, residual gravity, seismic velocity structure, and plate boundary reflection intensity) and described the geological environment of the slow-earthquake-genic regions (e.g., water sources, pressure–temperature conditions, and metamorphism). The integrated slow earthquake distribution enabled us to comprehensively discuss the role of slow earthquakes in the occurrence process of the Tohoku-Oki earthquake. The correspondences of the slow earthquake distribution with the crustal structure and geological environment provide insights into the slow-earthquake-genesis in the Japan Trench and imply that highly overpressured fluids are key to understanding the complex slow earthquake distribution. Furthermore, we propose that detailed monitoring of slow earthquake activity can improve the forecasts of interplate seismicity along the Japan Trench. [ABSTRACT FROM AUTHOR]

A modified k-nearest-neighbors method is introduced that provides an efficient nonlinear estimate of the intensity of a point process (field) based on locations of events. The method is applied to perform a detailed statistical analysis of the spatial structure of the seismic intensity field (in the context of this paper, the term "intensity" refers to the intensity of the seismic field, and should not be mistaken for the intensity of ground motion caused by an earthquake). The proposed method requires neither a preliminarily delineated area nor a normalization procedure for the estimates. In contrast to many interpolation methods, estimates based on the proposed method are statistically justified. The "uncertainty relation" between the spatial smoothing effect and random errors is established for the method in an explicit form. A procedure for choosing the number of nearest neighbors k* that controls the effective radius of smoothing is suggested. The proposed method is applied to analyze the seismic intensity field in two seismogenic regions surrounding the Kuril Islands and Japan during the period from 1904 to 2011. Spots of increased seismic activity in these regions are localized by the new method, and some quantitative statistical characteristics of these spots are determined and discussed. [ABSTRACT FROM AUTHOR]

This study summarizes the findings of an attitude survey focused on people's perceptions of seismic hazard maps, which illustrate the risk of an earthquake in each location throughout Japan. These seismic hazard maps depict the likelihood of an earthquake with a seismic intensity of "6 Lower" or more within 30 years, with 3.0% being considered a high possibility. The 3.0% occurrence probability within 30 years can be reworded to 2.0% occurrence probability within 20 years, 0.1% occurrence probability within a year, 4.9% occurrence probability within 50 years, or 39.4% occurrence probability within 500 years when being converted according to a Poisson distribution. In this study, we convert the occurrence probability within 30 years in the seismic hazard maps to obtain that within a year up to that within 1000 years, present the involved risk and demonstrate the yearly probability of the people who see the maps becoming most convinced of the need for countermeasures. Although those are shorter than the occurrence probability within 30 years anyway, it is a characteristic that the peaks existed at the occurrence probability within 10–20 years, not at the occurrence probability within one year or five years. However, the results changed according to the age of the people viewing the maps, and it was when the risk was presented as the occurrence probabilities within 20 and 30 years for the people in their 20–40 s, while it was when the risk was presented the occurrence probabilities within 10 years for the people in their 50–60 s, the perception toward the need of countermeasures increased the most. In addition, regardless of gender and place of residence (coast of the Sea of Japan or the Pacific coast), the perception toward the need of countermeasures peaked at the occurrence probabilities within 10 and 20 years. [ABSTRACT FROM AUTHOR]

Fluid migration in subduction zones is a key controlling factor of slow and megathrust earthquakes at plate boundaries. During the migration, seismic velocity and heterogeneous structures in its pathways may be temporarily perturbed, preferably triggering slow earthquakes. Here, we show that transient changes of seismic heterogeneity occurred 0–9 months before shallow slow earthquakes in the Nankai subduction zone, Japan, using very long‐term (6–10 years) records of ambient seafloor noise. The heterogeneity changes preceding to shallow slow earthquakes were observed near the margin of the source region, while concurrent changes primarily occurred in the source region. We propose that the heterogeneity changes are attributed to dynamic fluid migration, and the difference in timings reflects the pore pressure level in the corresponding source region. When fluids are supplied to a source region under relatively low pressure, fluids are leaked out from its downdip or updip side, and slow earthquakes occur not immediately but with a time delay of at most 9 months. In the high pore pressure case, slow earthquakes occur immediately with fluid migration from the source region. This study suggests that the heterogeneous seismic structure is possibly changed by fluid migration before slow earthquakes in the Nankai subduction zone. Plain Language Summary: While the linkage between fluid and slow earthquakes occurring at the plate boundary of subduction zones has been revealed, such a relationship for very shallow parts close to trench axes remains elusive. In this study, we investigated the temporal variations of seismic velocity and heterogeneous structure beneath the seafloor in the Nankai subduction zone, Japan, using the seismographs observed by a permanent cabled network starting in 2010. The intensities of seismic heterogeneous structures change 0–9 months prior to the shallow slow earthquakes, implying that the heterogeneous structure is altered by fluid migration that affects the slow earthquake generation. In the case of the fluid migration preceding to slow earthquakes, fluids are supplied to the source region with relatively low pore pressure levels, and the pore pressure level there increases until the timing of the slow earthquake generation. In contrast, the case of concurrent fluid migration corresponds to the fluids supplied to the source region with a relatively high pore pressure level, and slow earthquakes occur at the immediate timing of the fluid supply. These results suggest that monitoring heterogeneous seismic structures potentially contributes to further understanding of the spatio‐temporal relationship between fluid migration and shallow slow earthquakes. Key Points: Transient changes of seismic heterogeneities occurred 0–9 months before slow earthquakes in the shallow Nankai subduction zoneWe consider that the heterogeneity changes are caused by fluid migrationThe difference in timings between fluid migration and slow earthquakes reflects the pore pressure levels at the source regions [ABSTRACT FROM AUTHOR]

Deep low‐frequency earthquakes (LFEs) in Northeast Japan occur beneath active volcanoes at depths of 10–40 km. These volcanic LFEs radiate low‐frequency seismic waves, with most energy at 2–8 Hz, despite their low magnitudes (M < 2). Although many previous studies have obtained various focal mechanisms with non‐double‐couple components and suggested physical processes related to magma, the universal physical process is poorly understood. Therefore, we comprehensively determined the focal mechanisms of 264 LFEs for 26 volcanic regions in Northeast Japan using S/P amplitude ratios. Many of the obtained solutions have large double‐couple components with small compensated linear vector dipole components. Such source mechanisms can be explained by shear slip on the bending fault. We observed that the plunge of the null axis is as small as 20–30º at depths of 15–25 km, whereas it becomes larger and more varied at depths of 25–35 km. We interpreted that the regional stress field is relatively homogeneous in the middle of the crust, whereas it may be altered near the Moho discontinuity due to thermal stress or other effects related to potential magmatic processes. In addition, after quantitatively investigating the possible triggering of LFEs due to static stress changes in both the 2008 Iwate‐Miyagi earthquake and the 2011 Tohoku earthquake, we concluded that LFEs might have been triggered by substantial stress changes caused by large earthquakes in some regions. Plain Language Summary: Deep slow earthquakes occurring near active volcanoes are thought to be related to deep magmatism. However, their physical processes are not well understood because of the lack of observations. In this study, to reveal their universal processes, we determined the focal mechanisms of 264 events in 26 volcanic regions in Northeast Japan, where deep slow earthquakes occur actively, and high‐quality waveform data are available. Many of the obtained 264 focal mechanisms are dominated by shear slip components, similar to ordinary earthquakes. We found that the focal mechanisms of shallower events (<25 km) are consistent with the regional stress field in Northeast Japan, while those of deeper events (>25 km) vary. Such disturbances in the stress field at greater depths may be generated by stagnated magma near the Moho discontinuity. We also found that the activity of deep slow earthquakes is triggered by stress changes induced by large earthquakes. Key Points: Many of the 264 focal mechanisms of deep low‐frequency earthquakes in 26 regions have large double‐couple componentsThe plunge of the null axis is as small as 20–30º at 15–25 km, but it becomes larger and more diverse at 25–35 kmThe triggering potential of large earthquakes correlates with the activity changes of deep low‐frequency earthquakes [ABSTRACT FROM AUTHOR]

The 2011 off the Pacific coast of Tohoku Earthquake, with its epicenter off the Sanriku coast, measured the moment magnitude of 9.0, had a maximum seismic intensity of 7 in the northern part of Miyagi Prefecture, and impacted an area of 450 km. Consequently, a variety of unprecedented problems were made apparent. In particular, the human and property damage wrecked by the ensuing tsunami triggered our response for earthquake and tsunami resistance. In addition to conventional issues, such as earthquake resistance of buildings, disruption of lifelines, liquefaction of residential land and soil structures, and tsunami damage in coastal areas, there were new challenges, such as prolongation of earthquake disaster waste treatment. During the 10 years since the 2011 earthquake, tsunami countermeasures have been reexamined, and based on the concept of multiple protections, both tangible and intangible countermeasures have been advanced. This article addresses technical problems related to complex disasters, and includes the example of actual damage to a river levee in the Iwate Prefecture and the case of a building overturned by tsunami in Onagawa City, Miyagi Prefecture. It also discusses liquefaction caused by earthquakes and lists the points to be considered when selecting tsunami evacuation buildings to tackle future tsunami disasters. [ABSTRACT FROM AUTHOR]

On 21 October 2016, an earthquake with a magnitude of 6.6 (determined using the Japan Meteorological Agency's [JMA] seismic network) occurred in the center of Japan's Tottori Prefecture. In the city of Kurayoshi and in the towns of Yurihama and Hokuei, JMA seismic intensities of lower 6.0 were observed, and structural damage to housing was concentrated in a limited number of areas. This research conducted microtremor observations around damaged areas and used previous studies to estimate subsurface structures and ground motion characteristics. Low-velocity layers with an S-wave velocity of between 80 and 200 m/s were estimated at all observation sites and a tendency is present for the thickness to increase towards the coastal plains and decrease inland. In an evaluation of the relationship between ground motion characteristics and earthquake damage, researchers found that the occurrence of damage correlated to significant changes in layer thickness. Researchers believed that the damage correlates to the 2-D or 3-D effects of subsurface structures. [ABSTRACT FROM AUTHOR]

Considering spatial correlation of multiple earthquake intensity measures (IMs) is of particular importance in loss assessment of spatially distributed assets. This subject has been investigated in previous studies under the assumption of isotropy. Considering the fact that the assumption of isotropy is not valid in general, the present study employs a non-separable covariance model based on latent dimensions method to investigate anisotropic properties of spatial correlations and cross-correlations of intra-event residuals of multiple earthquake IMs. This method leads to the generation of valid covariance matrix in order to model anisotropic spatially distributed multivariate random fields. Two sets of IMs are considered in this study; the first set consists of peak ground intensity values (acceleration, velocity, and displacement), and the second set consists of spectral accelerations at three different periods. Data of 10 earthquake events in California and Japan are utilized in this study to estimate parameters of marginal and cross-covariance models. Moreover, parameters of covariance model of regional site condition, which is considered as average shear wave velocity of top 30 m of soil profile (Vs30), are obtained in order to investigate the effect of local sited conditions on spatial correlations of IMs. It is shown that maximum range and anisotropy ratio of covariance models of intra-event residuals of IMs are correlated with those of Vs30 values. Also, it is observed that the anisotropy direction of residuals of IMs is consistent with anisotropy direction of Vs30 values. Finally, predictive models are proposed to obtain marginal and cross-covariance functions for different earthquake IMs considering anisotropy. [ABSTRACT FROM AUTHOR]

An economic performance evaluation scheme of historic buildings that consider the effect of structural renovation is proposed to provide information facilitating to the selection of reasonable renovation methods for preserving historic buildings. Ground motion scenarios, herein referred to as "lifecycle earthquake scenarios" in accordance with the previous research, were simulated to represent the annual maximum earthquake intensity data from the year of decision‐making until the end year of the building's lifetime. Additionally, the structural characteristics of historic buildings with masonry infill walls as part of the structure were analyzed under the "lifecycle earthquake scenarios." Through a parametric analysis accounting for the change in structural characteristics and the repair costs in the lifecycle earthquake scenarios, the economic performance of historic buildings was calculated. Based on the results, the demand spectrum that satisfied the economic performance was obtained. This demand spectrum can provide the optimal structural renovation method to facilitate the building owner in making decisions regarding preservation. [ABSTRACT FROM AUTHOR]

For regional disaster prevention, it is important to understand the area of occurrence of strong ground motion and its occurrence probability. The spatial probabilistic seismic hazard analysis (SPSHA) proposed by the authors can provide this information. In SPSHA, the results are expressed as a relation between the area where a given seismic intensity is generated and the exceedance probability. Results obtained from such a probabilistic approach include the effects of various seismic sources. Therefore, to efficiently describe an earthquake scenario for regional earthquake countermeasures, it is necessary to understand the impact of each earthquake source. In this study, we propose a seismic hazard deaggregation for SPSHA, and present a method for quantitatively understanding the earthquakes that affect the target region. As a practical application, SPSHA is conducted for Kanagawa prefecture in Japan. We conducted seismic hazard deaggregation for whole and sub-area, and discussed the differences in dominant earthquakes among areas and the use of such information in disaster prevention. [ABSTRACT FROM AUTHOR]

A significant amount of work has been conducted in the Japanese islands on high-precision positioning, surveying, natural disaster mitigation, reference frame, and datum definitions; however, there is substantial scope for exploring the current seismotectonic activity of Japan, which would provide further awareness of disaster management. The short recurrence time of great inter-plate earthquakes and well-recorded geodetic observations provide one of the best examples to analyze the combination of contemporary deformation and seismic intensity in Southwest (SW) Japan. In the current study, we analyzed three districts of SW Japan which include mainly Kyushu district and parts of Chugoku and Shikoku districts. We predicted Global Navigation Satellite System (GNSS) measurements based on Amurian-fixed reference frame (AREF) velocities with the help of singular spectrum analysis (SSA) method and examined the regional deformation from April 01, 2010 to December 31, 2018. In addition, we analyzed the earthquakes clustered calculated by the nearest neighborhood distance method, which showed prominently bimodal seismicity of SW Japan and revealed the existence of two statistically distinct earthquake populations. The events inside a cluster were normally close to their nearest neighbors, whereas events from distinct clusters were comparatively aloof from each other. Finally, the paper provides the spatial strain and rotational rate variation for selected seismotectonic districts that are in relatively good agreement with the seismic deformation inferred from earthquake focal mechanisms. We believe that our integrated approaches would provide a better insight into the active deformation of SW Japan. [ABSTRACT FROM AUTHOR]

The seismic performance assessment of bridges by nonlinear time history analysis using unidirectional spectrum-matched accelerograms is generally adopted in Japan's specifications. However, the simultaneous action of two horizontal components is known to induce a potentially higher inelastic response in steel piers relative to that under unidirectional excitation. In this background, a rising concern within research communities is the bidirectional effect on the risk of bridge failure or damage under a given seismic intensity during the service life of a bridge. In this study, the difference in the risk of steel pier damage/failure between unidirectional ground motion and bidirectional ground motion is assessed using seismic fragility. Fragility curves are constructed by subjecting a single steel pier with various geometric designs to a large number of earthquake ground motions using the incremental dynamic analysis methodology. The study indicates that the damage state of collapse is not changed by bidirectional excitations, whereas the use of bidirectional excitations in less damaging states reduces the bridge seismic performance and induces higher fragility. The response difference is quantified by introducing an equifragility factor. This factor is calculated as the ratio of intensity of the unidirectional input to the bidirectional input, which causes the same fragility caused by the unidirectional counterpart. The constant characteristic value of the equifragility factor provides useful information for considering the bidirectional effect in seismic design. • Unidirectional analysis provides a low confidence in the predicted seismic demand. • Bidirectional excitations in less damaging states induces higher fragility. • Damage state of collapse is not changed by bidirectional excitations. • Consideration of the bidirectional effect in seismic design is proposed. [ABSTRACT FROM AUTHOR]

On 6 September 2018, a Mj 6.7 (Mw 6.6) earthquake with a focal depth of approximately 37 km and maximum seismic intensity of 7.0 on the Japan Meteorological Agency (JMA) scale (corresponding to approximately X on the Modified Mercalli Intensity (MMI) scale) struck the central and eastern Iburi regions of Hokkaido, Northern Japan, 1 day after the Typhoon Jebi passed through the region. Thousands of landslides were triggered and significant losses resulted from the earthquake sequence. A detailed landslide inventory map, including 5625 coseismic landslides, was delineated on the basis of 3307 published landslide sites. Most of the coseismic landslides are translational landslides of small to medium scale with high mobility and long run-out distance. Thirty-six people were killed by the landslides despite the afflicted area being sparsely populated. It is found that all the 5625 landslides spread in an elliptic area extending NNW/SSE, running approximately parallel to the strike of (active) faults in this region. The preferred aspect of the landslide-affected area is southerly, running nearly perpendicular to the NNW/SSE striking (active) faults. Most coseismic landslides are distributed in regions with seismic intensity of 7.0 to 8.0 (MMI Scale), with peak ground acceleration (PGA) of 0.4 to 0.7 g. Most of the coseismic landslides occurred at the elevation between 100 and 250 m, and the slope angle between 15° and 35°. Miocene sedimentary rock is the predominant bedrock type identified in the landslide area. Slope failures were triggered in stratified pyroclastic fall deposits, in the combination of strong seismic ground motion and intense antecedent precipitation. Sliding zone liquefaction phenomena were confirmed in the field investigation. The relationship between the old landslides (slope failures occurred prior to the Iburi earthquake) and the coseismic landslides is also discussed in this study. [ABSTRACT FROM AUTHOR]

The spatial correlation of the ground deformation at Mt. Tawarayama in Kumamoto City in Japan with the seismic damages of Tawarayama tunnel was developed to explore whether the seismic damages of underground structures are related to the ground deformation. A pair of digital elevation model data sets were captured from the high-density airborne light detection and ranging data before and after the 2016 Kumamoto earthquake. A new variant of iteratively closest point (ICP) algorithm named combination and classification ICP was introduced to detect the three-dimensional ground deformation field. The seismic damages of Tawarayama tunnel caused by the earthquake were studied via site investigation. The results indicated that the strong ground deformation can reflect the seismic performance of the tunnel to some extent. Furthermore, the results of the ground deformation direction validated the assumption of seismic wave propagation along the tunnel. It gives a clear explanation for the mechanism of the seismic damages under the earthquake force, especially lining cracks, pavement damage, and construction joint damage. [ABSTRACT FROM AUTHOR]

Highlights • Ground-motion duration and spectral shape affect the seismic performance of SCBFs. • Most inside-basin ground motions caused damage states at lower spectral acceleration. • A combined intensity measure reduces uncertainty in the damage fragility functions. • Basin effects should be considered in structural design. Abstract Deep sedimentary basins are known to increase the intensity of ground motions, but this effect is not explicitly considered in the seismic design values used in the U.S. building codes. In the Pacific Northwest, the basin amplification of ground motions from subduction zone interface earthquakes is particularly important, because such earthquakes contribute significantly to the seismic hazard at natural periods for which basin amplification is high. Additionally, interface earthquakes have long durations, the effects of which are also not considered in building codes. Research into seismicity of these regions has been plentiful but few studies have evaluated the impact on the built environment. Using advanced nonlinear modeling approaches, a commonly used system, special concentrically braced frames, was studied with an eye towards comparing the performance of crustal and subduction-zone earthquakes. Using standard performance and collapse-assessment procedures, 3-, 9-, and 20-story SCBF archetypes were subjected to large-magnitude interface earthquakes recorded in basins in Japan; these motions were selected because they were recorded in locations with similar depths as the Seattle basin. The results demonstrate that deep basins in combination with the long ground-motion duration results in brace fracture at lower spectral accelerations, S a. Similarly, collapse is associated with lower values of S a. The results suggest that the strength of the archetypes inside deep basins and subjected to interface earthquakes would need to be increased by a factor of over 2.0 to ensure similar collapse probabilities as those located outside basins and/or subjected to crustal earthquake hazards. The results are similar to those obtained for other seismic resisting systems previously studied. [ABSTRACT FROM AUTHOR]

The source rupture process of the 2016 central Tottori, Japan, earthquake ( M 6.6) was estimated from strong motion waveforms using a multiple-time-window kinematic waveform inversion. A large slip region with a maximum slip of 0.6 m extends from the hypocenter to the shallower part, caused by the first rupture propagating upward 0-3 s after rupture initiation. The contribution of this large slip region to the seismic waves in the frequency band of the waveform inversion is significant at all stations. Another large slip region with smaller slips was found in north-northwest of the hypocenter, caused by the second rupture propagating in the north-northwest direction at 3-5 s. Although the contribution of this slip region is not large, seismic waveforms radiating from it are necessary to explain the later part of the observed waveforms at several stations with different azimuths. The estimated seismic moment of the derived source model is 2.1 × 10 Nm ( M 6.1). The high-seismicity area of aftershocks did not overlap with large-slip areas of the mainshock. Two wave packets in the high frequency band observed at near-fault stations are likely to correspond to the two significant ruptures in the estimated source model. [ABSTRACT FROM AUTHOR]

Background: The Great East Japan Earthquake occurred at 2:46 p.m. on March 11, 2011. The epicenter was off the coast of Miyagi prefecture, and the magnitude of the earthquake was 9.0 with a maximum seismic intensity of 7.0. Although it has already been four years, victims continue to have complex problems. In the stricken areas of Miyagi prefecture, almost ten percent of the residents continue to live in temporary housing. Life altering events that force relocation and a change of living environment are known to adversely affect mental health. The purpose of this study was to examine the mental health of mothers of infants who experienced this disaster in Miyagi prefecture. Methods: We conducted a survey using The Edinburgh Postnatal Depression Scale (10 months) and The General Health Questionnaire-28, an efficient screening tool for psychiatric distress. Eight hundred eighty-six mothers of children born from February to October, 2011 in Miyagi prefecture were surveyed 10, 16, 24, 36 and 48 months after the disaster. Data were analyzed with the use of SPSS 21.0 J for Windows. The study was approval by the review board of ethics at Tohoku University. Results: The questionnaire was answered by the following number of mothers at the specified months after the disaster: 677 at 10 months, 384 at 16 months, 351 at 24 months, 250 at 36 months and 193 at 48 months. Results at all time periods indicated a high prevalence of psychiatric distress among the mothers surveyed. The percentage of Japanese adults with high-risk GHQ-28 scores is 14 %, thus psychological distress among the subjects in the present study is considerably more widespread. General Health Questionnaire-28 scores were significantly higher for those mothers experiencing dissatisfaction in their marital relationships. We found that mothers have experienced severe mental distress since the disaster, which we think is a possible cause of depression that is leading to poor mental health. Conclusion: The results indicate that the upheaval caused by the tsunami affected the mental health of the mothers. Psychological distress continued to be prevalent up to four years after the disaster. Different factors were found to be associated with their distress. The most common issues were economic problems, dissatisfaction in the marital relationship, and no support with childcare. [ABSTRACT FROM AUTHOR]

We propose early-warning system for reducing tsunami refuge using the data of the magnitude and the depth informed by the Earthquake Early Warning (EEW) by Japan Metrological Agency (JMA). The EEW provides advance announcement of the estimated seismic intensity and expectSed arrival time at the just points and regions before arriving strong motion. The hypocenter and magnitude of the earthquake are estimated by using wave form data observed by seismographs near the epicenter. Inukai et al. (2009) proposed the method to determine whether generate tsunami using scaling relation between magnitude and depth of hypocenter. The probability of tsunami generating is calculated by using the EEW information (magnitude and depth) and the Inukai's scaling relations. In this method, the information of probability of tsunami generating is issued in a few seconds after EEW. We incorporated this method into our system and verified validity of our system. [ABSTRACT FROM AUTHOR]

The implementation of a new Tsunami Intensity Scale is proposed because a vast amount of data has been collected from the two megatsunamis that took place in the Indian Ocean in 2004 and northeast Japan in 2011. The newly proposed scale is 12-grade and is based on the assessment of a large number of objective criteria that are easily accessible and incorporated into six groups. As a result, it does not saturate as six-grade scales do. More specifically, the estimation of intensity values takes into account: (1) the quantities of the phenomena, (2) the direct impact on humans, (3) the impact on mobile objects, (4) the impact on coastal infrastructure, (5) the impact on the environment, and (6) the impact on structures. The new scale is compatible with the widely used EMS1998 and ESI2007 scales and has a reliable horizontal correspondence throughout the groups of criteria. It is easily and directly applicable to all environments, and particularly useful for the outlining of microzones of different intensities in any tsunami-affected area. It can be implemented for any land use/cover type, such as urban, rural, industrial, touristic, and so on, and at the same time, morphologic diversity of affected areas is not an obstacle to application. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to propose a new index for the seismic damage estimation of service lines. The proposed index is based on the tension of each service line due to an earthquake event. Because the tension is evaluated using not only the seismic intensity, but also the dynamic properties of the major components of the distribution equipment, including poles, lines, transformers, and service lines, the proposed index makes it possible to quantitatively differentiate the seismic damage level of every distribution pole. Using the records of seismic damage caused by the 2007 Niigata-ken Chuetsu-oki earthquake, the estimation accuracy of the proposed index is compared to that of existing damage indices. It is shown that the proposed index is more suitable than existing indices for equipment damage estimation. © 2012 Wiley Periodicals, Inc. Electron Comm Jpn, 95(9): 17-26, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.11400 [ABSTRACT FROM AUTHOR]

Abstract: , hereafter cited as H&H, report the observation of anomalous increases in the ULF geomagnetic field spectral density ratio which the authors claim to be possible precursors of the 2008 Iwate–Miyagi Nairiku earthquake. Here the results of H&H are reviewed taking into account the global geomagnetic activity level by means of ∑Kp index. This paper cast serious doubts on the seismogenic origin of the magnetic signatures documented by H&H showing that the anomalous signals are normal ULF magnetic variations induced by solar–terrestrial interaction. In summary, H&H’s claims that magnetic field disturbances about a month before the Mw 6.9 Iwate–Miyagi Nairiku earthquake on June 13, 2008 are precursors to the earthquake are unlikely to be correct. [Copyright &y& Elsevier]

We have estimated broadband (f = 0.5-8 Hz) site amplification factors at 1800 sites in Japan based on the coda normalization method using 4001 seismo-grams obtained from 48 events. The results show that, in the low-frequency band (f = 0.5-1 Hz), the site amplification factor varies over a wide range from -4 to 24 dB, with larger site amplification factors (> 8 dB) in such major basins as Kushiro, Rumoi, Sapporo, Aomori, Sendai, Niigata, Tokyo, Toyama, Nagoya, Osaka, Oita, and Kagoshima. On the other hand, the site amplification factor in the high-frequency band (f = 4-8 Hz) varies over a relatively narrow range from 0 to 18 dB at each station and has no clear correlation with the surface geology of each station. We then examined the contribution of the site amplification at each station to the anomalous distribution of the intensity pattern during large earthquakes by correcting the observed ground accelerations at each K-NET and KiK-net station with their corresponding estimated site amplification factors. The corrected pattern of intensity shows simple concentric isoseismal intensity contours around the hypocenter, indicating the applicability of our estimates to strong motion predictions. We confirmed that our estimates are superior to those derived from geology, such as those based on the regression of the averaged 5-wave velocity from the surface to a depth of 30 m (VS30), with a smaller standard deviation of intensity variations based on a standard decay function of intensity versus hypocentral distance. [ABSTRACT FROM AUTHOR]

Relationships between collapse ratios (CRs) of buildings and characteristics of strong ground motions during the 2008 Wenchuan earthquake was founded. Vulnerability functions of buildings were established in relation to PGA, PGV, PSA, and PPSv. Damage criteria for CR<10% corresponding to 'minor and moderate damage' were PGA<250 gal, PGV<25 cm/s, PSA<900 gal, and PPSv<50 cm/s. For CR>50%, corresponding to the 'extremely serious damage' were PGA>600 gal, PGV>55 cm/s, PSA>2200 gal, and PPSv>120 cm/s. Seismic damage during the Wenchuan earthquake was heavier than that of the 1995 Kobe and 1999 Chi-Chi earthquakes for the same levels of ground motion. [ABSTRACT FROM AUTHOR]

The article focuses on a new ground motion prediction equation (GMPE) for Japan Meteorological Agency (JMA)'s instrumental seismic intensity measure (IJMA), based from the strong motion database and functional forms used to create similar peak response parameter GMPEs in relation to the Next Generation Attenuation (NGA) project of the Pacific Earthquake Engineering Research Center (PEER). The new GMPE shows good agreement with all of the relationships at 7.0 moment magnitude (M) when compared to relationships created for crustal and shallow subduction earthquakes, but has poor agreement at small magnitudes. Furthermore, the new GMPE offers conservative or upwardly biased IJMA estimates for less than 5.5 M as it predicts the highest entities at small magnitudes.

Abstract: The Japan Meteorological Agency commenced an Earthquake Early Warning (EEW) provision service in August 2006 to advanced users and in October 2007 to the Japanese public. By the end of 2009, EEWs had been issued to advanced users for more than 2100 earthquakes and to the public for 11 earthquakes. Nearly 80% of seismic intensity predictions were accurate within ±1 intensity unit on JMA’s Seismic Intensity Scale. The Iwate-Miyagi Nairiku Earthquake in 2008 demonstrated the efficiency of EEWs in many places. However, there were other cases where the warnings were not issued in time for strong tremors. Further technical development is needed for both earthquake source parameter estimation and seismic intensity prediction. Public education in regard to the technical limitations and accuracy of EEWs as well as actions to take in response to such warnings are also indispensable. [ABSTRACT FROM AUTHOR]

The article focuses on the history of the contribution of shaking tables in the advancements in earthquake engineering. It states that one of the significations of experimental device shaking tables in the earthquake engineering, is that they replicate the true nature of the earthquake input. It mentions that these devices apply the ground motion to the base of a structure and induce the inertia forces in the element of its mass. It adds that the Froude and the Cauchy numbers for the model and prototype must be equal to the ratio of gravity and the dynamic inertia forces. Meanwhile, it says that the first laboratory experiments regarding the impact of earthquakes on the structural models were conducted by Englishman John Milne and Japanese Fusakichi Omori in Japan in 1890.

We developed a recipe for predicting strong ground motions based on a characterization of the source model for future crustal earthquakes. From recent developments of waveform inversion of strong motion data used to estimate the rupture process, we have inferred that strong ground motion is primarily related to the slip heterogeneity inside the source rather than average slip in the entire rupture area. Asperities are characterized as regions that have large slip relative to the average slip on the rupture area. The asperity areas, as well as the total rupture area, scale with seismic moment. We determined that the areas of strong motion generation approximately coincide with the asperity areas. Based on the scaling relationships, the deductive source model for the prediction of strong ground motions is characterized by three kinds of parameters: outer, inner, and extra fault parameters. The outer fault parameters are defined as entire rupture area and total seismic moment. The inner fault parameters are defined as slip heterogeneity inside the source, area of asperities, and stress drop on each asperity based on the multiple-asperity model. The pattern of rupture nucleation and termination are the extra fault parameters that are related to geomorphology of active faults. We have examined the validity of the earthquake sources constructed by our recipe by comparing simulated and observed ground motions from recent inland crustal earthquakes, such as the 1995 Kobe and 2005 Fukuoka earthquakes. [ABSTRACT FROM AUTHOR]

It is an acquired result that, in order to enable realistic earthquake hazard assessment and reliable estimation of the ground motion response to an earthquake, three-dimensional velocity models have to be considered. In this paper we present a new analytical procedure for determining the seismic wavefield in a 3D anelastic model based on the combination of the ray theory with the modal summation method. The proposed procedure has been validated by considering the three-dimensional model of the Kanto basin (Japan) available in the literature. Three-dimensional simulations were performed for the 1990 Odawara earthquake. The results obtained were compared both with recorded signals and with simulations available in the literature for several stations located within the Kanto basin. Besides the advantage of being a useful tool for assessment of seismic hazard and seismic risk reduction, it is characterized by high efficiency, in fact, once the study region is identified and the 3D model is constructed, the computation, at each station, of the three components of the synthetic signal (displacement, velocity, and acceleration) takes less than 3 h on a 2 GHz CPU. [ABSTRACT FROM AUTHOR]

For a quick and stable estimation of earthquake damaged buildings worldwide, using Phased Array type L-band Synthetic Aperture Radar (PALSAR) loaded on the Advanced Land Observing Satellite (ALOS) satellite, a model combining the usage of satellite synthetic aperture radar (SAR) imagery and Japan Meteorological Agency (JMA)-scale seismic intensity is proposed. In order to expand the existing C-band SAR based damage estimation model into L-band SAR, this paper rebuilds a likelihood function for severe damage ratio, on the basis of dataset from Japanese Earth Resource Satellite-1 (JERS-1)/SAR (L-band SAR) images observed during the 1995 Kobe earthquake and its detailed ground truth data. The model which integrates the fragility functions of building damage in terms of seismic intensity and the proposed likelihood function is then applied to PALSAR images taken over the areas affected by the 2007 earthquake in Pisco, Peru. The accuracy of the proposed damage estimation model is examined by comparing the results of the analyses with field investigations and/or interpretation of high-resolution satellite images. [ABSTRACT FROM AUTHOR]

Abstract: The long-term data during seven years from January 2001 to December 2007, as observed by the Pacific VLF/LF network consisting of several Japanese stations and one station in Kamchatka, are extensively utilized to perform a statistical correlation study between the lower ionospheric perturbations as detected by subionospheric propagation and earthquakes (EQs). In this paper, we adopt a physical parameter, the maximum seismicity intensity observed (I) to define the strength of an EQ unlike the previously and conventionally used EQ magnitude and depth, which is a combined effect of EQ magnitude and depth, together with the Earth’s surface information and geological condition around the EQ epicenter. After considering EQs only take place on the land because of the use of seismicity and by using the superimposed epoch analysis, it is found for the larger EQs with I from 5 to 7 (we feel serious trembling and we expect serious damage) that the most important VLF/LF parameter, trend (nighttime average amplitude), shows a definite decrease about 10 days before the EQ by exceeding 2σ (σ: standard deviation) criterion; the dispersion shows a maximum about 10 days before the EQ but not exceeding 2σ line and finally the nighttime fluctuation shows an enhancement about 10 days before the EQ (with exceeding the 2σ level). A definite statistical correlation is confirmed between the ionospheric perturbations and I when I is strong enough in a range from 5 to 7. Whereas, there is no significant correlation between the two when I is in a range from 3 to 4. Finally, together with the corresponding results for EQs in the sea, but close to the land, these results are discussed in the light of lithosphere–ionosphere coupling mechanism. [Copyright &y& Elsevier]

Abstract: In November 2005, we conducted the first low-altitude, high-density helicopter-borne aeromagnetic survey over Sakurajima Volcano, Kyushu, Japan to provide a baseline for subsequent measurement of changes in magnetic anomalies related to volcanic processes, because previously acquired aeromagnetic data cannot resolve small-scale geological feature. Although the observation error was considered to be <10 nT, the harmonic component is extracted by the reduction procedure. We applied an apparent magnetization intensity mapping method to the newly obtained aeromagnetic data assuming that magnetization intensity varies only laterally. Results showed the following features: (1) Apparent magnetization intensities of lava flows were from 4.0 to 6.0 A/m. The most remarkable highs (>5.0 A/m) were located on the lava around An''ei craters and on the northeastern flank of Kita-dake, (2) the lowermost values of apparent magnetization (<2.0 A/m) are locally distributed around the active craters of Minami-dake, suggesting high temperature in the shallow part and (3) apparent magnetization lows (~2.5 A/m) lie over the northwestern flank of Kita-dake, reflecting debris flows and/or volcanic fans. To examine the validity of the obtained map, we carried out rock-magnetic studies. The total magnetization intensities for the surface-rocks showed reasonable correlation with the mapped values. [Copyright &y& Elsevier]

Abstract: Earthquakes in active-folding zones often trigger long-lasting landform changes. Since an underground structure closely follows the motion of its surrounding soils and rocks even after it was damaged in an intense earthquake, experts in charge of reconstruction have to wait until they are convinced that the soils and rocks have been stabilized. Kizawa tunnel was seriously cracked during the 23 October 2004 Mid-Niigata Earthquake. The upper half of the tunnel''s cross-section near the north mouth shifted about 0.5m sideways. Since a ring-shaped cross-section of a tunnel sustains the surrounding soil pressure, this crack pattern seemed to be serious. The authors collaborated with the Nagaoka Regional Development Bureau, Niigata Prefectural Government, in investigating the causes of the damage and in conducting long-term observation of the soils and rocks. This paper summarizes some findings for rational rehabilitations through the investigations. [Copyright &y& Elsevier]

On the background of seasonal and heliogeomagnetic disturbances, disturbances of the ionization density near noon connected to earthquakes are investigated. The study is performed for some tens of earthquakes with magnitudes M>5 and depths h<70 km, which occur at distances from the vertical sounding stations "Tokyo", "Akita", and "Yamagawa" not larger than R=exp(M)+150 km. The analysis is performed using data registered by the three sounding stations every hour during 30 years. Especially methods of the statistical analysis are applied to search for regularities in the lithospheric-ionospheric links before and after earthquakes. The growth of the mean ionization density N at the F-layer electron density maximum Fof2 five-three days before earthquakes, and the decrease of N approaching the eruption and during a few days after the earthquake is investigated in dependence on both the magnitude of the earthquake M and the ionization density N near the F-layer maximum. It is found that some days before earthquakes the decrease of the ionization density ΔN is proportional to the values of M and N. After the earthquakes, ΔN depends much weaker on the magnitude M, and it is not influenced by the ionization density N. The variations of the ionization density three days before earthquakes do not depend on N and M (within the same order of approximation). [ABSTRACT FROM AUTHOR]

Free-air gravity anomaly in plate subduction zones, characterized by island-arc high, trench low and outer-rise gentle high, reflects the cumulative effects of long-term crustal uplift and subsidence. In northeast Japan the island-arc high of observed free-air gravity anomaly takes its maximum about the eastern coastline. On the other hand, the current vertical crustal motion estimated from geological and geomorphological observations shows a gentle uplift in the land area and steep subsidence in the sea area with the neutral point near the eastern coastline. Such a discrepancy in spatial patterns between the free-air gravity anomaly and current vertical crustal motion can be ascribed to a change in the mode of crustal uplift and subsidence associated with the initiation of tectonic erosion at the North American-Pacific plate interface. We developed a realistic 3-D simulation model of steady plate subduction with tectonic erosion in northeast Japan on the basis of elastic/viscoelastic dislocation theory. Through numerical simulations with this model we found that simple steady plate subduction brings about the crustal uplift characterized by island-arc high with its maximum about the eastern coastline, while steady plate subduction with tectonic erosion, which is represented by the landward retreat of the plate interface, brings about gentle uplift in the land area and steep subsidence in the sea area with the neutral point near the eastern coastline. Therefore, if we suppose that tectonic erosion started 3–4 million years ago after the long duration of simple steady plate subduction, we can consistently explain both patterns of free-air gravity anomaly and current crustal uplift in northeast Japan. [ABSTRACT FROM AUTHOR]

Unusually large (>5 cm) and prolonged shaking associated with longperiod ground motions at periods of about 7 sec were observed in central Tokyo during the Mw 6.6 Niigata-ken Chuetsu earthquake of 23 October 2004. The longperiod ground motions caused significant resonance in high-rise buildings of about 70 floors in height. Thus, it is an urgent matter to understand the development and amplification properties of long-period ground motions in Tokyo associated with large earthquakes. In this study, we use numerous waveform records from 585 stations in a nationwide accelerometer network (K-NET, KiK-net) and 495 intensity meters in the area around Tokyo. The data reveal that the long-period ground motion is characterized in most part by a surface, Rayleigh wave generated at the northern edge of Kanto basin, and the surface wave is developed as propagating through a thick cover of sediments (>3000-4000 m) that overlies rigid bedrock. To complement the observational data, we conducted a large-scale computer simulation of seismic-wave propagation by employing the Earth Simulator supercomputer with a detailed source-slip model and a high-resolution 3D sedimentary structural model of central Japan. The results of the computer simulation demonstrate that the anomalously prolonged ground shaking of the long-period signal recorded in the center of Tokyo occurred because of the stagnation of seismic energy resulting from the multipathing and focusing of Rayleigh waves toward the bottom of the Kanto basin from surrounding mountain regions with interaction to the 3D basin structure. [ABSTRACT FROM AUTHOR]

Following the 1995 Hyogo-ken Nanbu Kobe. Earthquake, the Japanese government, in an effort to prevent future earthquake disasters, installed networks consisting of a large number of strong-motion observation stations. Further, national seismic hazard maps were made available to the public on an Internet website in March 2005 by the Headquarters for Earthquake Research Promotion. However, these maps indicate only the local seismic intensity for Japan, as empirically convened from predicted peak velocity in consolidated soils. For various applications, other strong-motion indexes such as the response spectral acceleration are required. In this study, a database of whole Japanese strong ground motion records between 1963 and 2003 is established in order to identify a new standard attenuation relation for Japan, for response acceleration as well as peak value. It is usually very difficult to determine a suitable model form due to the large variability of strong-motion data and correlation among the model variables, because the strong coupling of variables in an attenuation model, and the statistical power of the data is often not large enough to determine the necessity of these parameters. Therefore, in this study, our model has only three variables: earthquake magnitude, shortest distance to the seismic fault plane, and focal depth. To improve predictions given by the model, site correction terms are adopted and additional terms for correcting regional anomalous seismic intensity with respect to the base model are determined. The good fit between the model and observed strong-motion records suggests that the new model is reasonably robust. [ABSTRACT FROM AUTHOR]

A spectral acceleration attenuation rnodel for Japan is presented in the present study. The data set includes a very large number of strong ground-motion records up to the 2003 Off Tokach main and aftershocks. Site class terms, instead of individual site correction terms, are used. The site classes of recording stations are from a recent study on site classification for strong-motion recording stations in Japan according to a classification scheme that has been used in Japanese engineering design. The use of site class terms enables tectonic source-type effects to be identified and accounted for in the present model. The effects of a faulting mechanism for crustal earthquakes also are accounted for. For crustal and interface earthquakes, a simple form of an attenuation model (with respect to distance) is able to capture the main strong-motion characteristics and achieves unbiased estimates. For subduction slab events, a simple distance modification factor is employed to achieve plausible and unbiased predictions. The effects of source depth, tectonic source type, and faulting mechanism of crustal earthquakes are significant. The need for magnitude-squared terms is evaluated, and the use of magnitude-squared terms reduces the interevent error further. [ABSTRACT FROM AUTHOR]

A probabilistic seismic hazard assessment was performed for the Japanese islands and surrounding areas. Seismic hazard parameters characteristic of the seismic history of the regions were obtained. The probability of occurrence of a large M ≥ 7 earthquake within a 10- and 50-year period was also calculated. Regions of very high levels of hazard occur where the Pacific, Phillipine and Eurasian Plates meet. High probabilities of occurrence of a large M ≥ 7 earthquake within a 10- and 50-year period occur within the region where the Pacific Plate subducts with the Eurasian Plate. [ABSTRACT FROM AUTHOR]

A seismic waveform inversion algorithm is proposed for the estimation of elastic soil properties using low amplitude, downhole array recordings. Based on a global optimization scheme in the wavelet domain, complemented by a local least-square's fit operator in the frequency domain, the hybrid scheme can efficiently identify the optimal solution vicinity in the stochastic search space, whereas the best-fit model detection is substantially accelerated through the local deterministic inversion. Results presented for selected aftershocks of the M w 7.0 Sanriku-Minami earthquake in Japan, recorded by the Kik-Net Strong Motion Network, illustrate robustness of the impedance structure estimation. By contrast, the attenuation structure is shown to be sensitive to the frequency content of seismic input data, attributed to the deterministic description of the continuum in the forward model that cannot simulate late arrivals of multiple-scattered energy. Sensitivity analyses illustrate that for the same forward model, results can be substantially different based on the definition of the objective function. It is concluded that even for engineering purposes, inversion should aim to decouple intrinsic and scattering attenuation mechanisms. [ABSTRACT FROM AUTHOR]

This article is concerted with objective estimation of the spatial intensity function of the background earthquake occurrences from an earthquake catalog that includes numerous clustered events in space and time, and also with an algorithm for producing declustered catalogs from the original catalog. A space-time branching process model (the ETAS model) is used for describing how each event generates offspring events. It is shown that the background intensity function can be evaluated if the total spatial seismicity intensity and the branching structure can be estimated, In fact the whole space-time process is split into two subprocesses, the background events and the clustered events. The proposed algorithm combines a parametric maximum likelihood estimate of the clustering structures using the space time ETAS model and a nonparametric estimate of the background seismicity that we call a variable weighted kernel estimate. To demonstrate the present methods, we estimate the background seismic activities in the central region of New Zealand and in the central and western regions of Japan, then use these estimates to produce catalogs of background events. [ABSTRACT FROM AUTHOR]