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To reveal the connections between the 2024 moment magnitude (Mw) 7.5 Noto earthquake in Japan and the seismicity swarms that preceded it, we investigated its rupture process through near-source waveform analysis and source imaging techniques, combining seismic and geodetic datasets. We found notable complexity in the initial rupture stages. A strong fault asperity, which remained unbroken in preceding seismic swarms, slowed down the rupture. Then, a second rupture initiated at the opposite edge of the asperity, and the asperity succumbed to double-pincer rupture fronts. The failure of this high-stress drop asperity drove the earthquake into a large-scale event. Our observations help unravel the crucial role of fault asperities in controlling swarm migration and rupture propagation and underscore the need for detailed seismological and interdisciplinary studies to assess seismic risk in swarm-prone regions. [ABSTRACT FROM AUTHOR]

This study explored closed-circuit television (CCTV) networks in northeastern Toyama Prefecture, Japan, as a new data source for tsunami detection following the 2024 Noto Peninsula earthquake. We analyzed CCTV footage and extracted time-series water level fluctuations at Yokoyama, Shimoiino, and Ekko. Spectral analysis of these waveforms revealed several long-period peaks (more than 100 s) in power spectral density (PSD), suggesting the presence of tsunami components. Notably, relatively large PSD peaks at approximately 5–10 min were observed at all CCTV locations in this study and at offshore wave observation points (Tanaka and Toyama). At Yokoyama, a maximum run-up of approximately 3 m was confirmed around 16:28. Although water level fluctuations at Shimoiino and Ekko were detected, identifying tsunami components proved challenging due to their small magnitude compared to other wave components. Despite these challenges, this study demonstrates the potential of CCTV networks for tsunami detection, and further research is needed to achieve real-time detection. [ABSTRACT FROM AUTHOR]

Volcanic earthquakes provide essential information for evaluating volcanic activity. Because volcanic earthquakes are often characterized by swarm-like features, conventional methods using manual picking require considerable time to construct seismic catalogs. In this study, using a machine learning framework and a trained model from a volcanic earthquake catalog, we obtained a detailed picture of volcanic earthquakes during the past 12 years at the Kirishima volcano, southwestern Japan. We detected ~ 6.2 times as many earthquakes as a conventional seismic catalog and obtained a high-resolution hypocenter distribution through waveform correlation analysis. Earthquake clusters were estimated below the craters, where magmatic or phreatic eruptions occurred in recent years. Increases in seismic activities, b values, and the number low-frequency earthquakes were detected before the eruptions. The process can be conducted in real time, and monitoring volcanic earthquakes through machine learning methods contributes to understanding the changes in volcanic activity and improving eruption predictions. [ABSTRACT FROM AUTHOR]

A combination of receiver function (RF) analysis and shear wave splitting can reveal the anisotropic properties of the Earth's velocity structure. The RF profile exhibits harmonic patterns partially generated from the discontinuities of anisotropic media near the receiver. The anisotropic properties are determined using splitting parameters, which include the fast polarization direction (FPD) and split time. We utilized the seismograms recorded by stations on Shikoku Island, Japan. Also, we applied the Bayesian information criterion to control the spike count of each RF, which consists of a series of spikes generated by time‐domain iterative deconvolution. Anisotropic differences arose between northern and southern regions along the 30‐km iso‐depth line of the top surface of the Philippine Sea Plate. In the southern part of Shikoku Island, the FPDs are sub‐perpendicular to the plunge of the subducting slab, while in the northern part, they are sub‐parallel to the plunge of the slab. Our results indicate that anisotropic strengths are weaker in the tectonic‐tremor band in northwestern Shikoku and stronger in the northern part of central and eastern Shikoku around the no tectonic‐tremor area. These anisotropic variations may characterize Shikoku Island's geological structure. Plain Language Summary: Receiver function (RF) analysis is sensitive to subsurface discontinuities in seismic velocity using shear waves on seismograms. This study estimated a seismic velocity anisotropy by combining RF and shear wave splitting analysis to determine the polarization direction and delay time, characterizing the anisotropic medium. The observed fast direction of anisotropy aligns with the strike of the subducting Philippine Sea Plate in southern Shikoku, while in the northern region, it becomes sub‐parallel to the subducting plate's plunge (N‒S). Additionally, the delay time between the split fast and slow shear waves indicates the strength of anisotropy. In the tectonic‐tremor‐clustered area in northwestern Shikoku, the strengths of anisotropy are regionally weaker than in other areas. Moreover, stronger anisotropy was measured in the deeper northern part of central and eastern Shikoku, where there is a lack of tectonic‐tremor activity. Although several factors contribute to the anisotropy, we concluded that the anisotropy mainly reflects the structure, including the subducting slab, continental crust, and even the mantle wedge. Key Points: Fine‐resolution anisotropic properties have been calculated above slab Moho in Shikoku Island, southwest Japan, using receiver function analysisWeaker anisotropic strength was observed in tectonic‐tremor‐clustered areas with serpentinized mantle wedge, especially in northwestern ShikokuSerpentinization of the mantle and metasomatic reactions lead to hydrofracturing and relatively low anisotropic strength [ABSTRACT FROM AUTHOR]

Crustal earthquakes are generally recognized as having recurrence periods of more than 1000 years. However, in northern Ibaraki Prefecture, Japan, two moderate-sized earthquakes occurred on almost the same fault plane in 2011 and 2016. Moreover, it has been reported that the slip distributions derived from crustal deformation data from these two events are almost identical. We performed a near-field waveform inversion analysis to estimate the details of the spatiotemporal distribution of the co-seismic rupture. Our results reveal large slip areas during each earthquake at different locations across the bend of the fault plane. These results indicate that the shear stress of the fault area where the main slip occurred during the 2011 event was not rebuilt in such a short period, a phenomenon that had not previously been discussed for this sequence. Our results also suggest that the fault geometry affected such complex fault ruptures. [ABSTRACT FROM AUTHOR]

In order to improve the electrical performance of the inverter system and make its output waveform close to a sinusoidal waveform, an inverter based on a linear phase‐shifting transformer is proposed, which can eliminate the low harmonics with opposite phase by the effect of phase shift and superposition. Firstly, the components and working process of the multiple superposition inverter system are introduced, and the working principle and winding structure of the linear phase‐shifting transformer are analyzed; Secondly, the Fourier decomposition of the inverter output voltage is carried out to obtain the harmonic currents at the same frequency as it, and it is demonstrated that the inverter is capable of eliminating most of the harmonics below the 23rd order by calculating the magneto‐dynamic potential synthesized in the air gap; Again, in order to overcome the harmonic electric potential caused by the edge‐end effect and the tooth slot structure of the linear phase‐shifting transformer, the secondary side winding of the linear phase‐shifting transformer adopts a short pitch structure, and it is proved that this structure has a significant suppression effect on the 5th and 7th harmonics without reducing the fundamental wave amplitude; Then, the model of multiple superposition inverter system is built based on Maxwell simulation software, and the effectiveness of the inverter device and winding structure on harmonic suppression is proved through spectral analysis of voltage waveforms with different load types and power factors; Finally, its reasonableness and accuracy are verified by experiments. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Recent observations beneath central Japan have shown that periodic fluid drainage occurs during slow‐slip events (SSEs) based on temporal variations in QP−1 ${Q}_{P}^{-1}$ above the megathrust boundary of the subducting Philippine Sea slab. However, no previous studies have estimated associated QS−1 ${Q}_{S}^{-1}$. A comparison of QP−1 ${Q}_{P}^{-1}$ and QS−1 ${Q}_{S}^{-1}$ can provide clues to the mechanism of seismic attenuation because of different propagation characteristics of the two waves. We estimate temporal variations in QP−1 ${Q}_{P}^{-1}$ and QS−1 ${Q}_{S}^{-1}$ via spectral analyses of waveform data from November 2009 to August 2021 period. The results indicate that both QP−1 ${Q}_{P}^{-1}$ and QS−1 ${Q}_{S}^{-1}$ exhibit temporal variations at about 1‐year periodicity and there are systematic differences between QP−1 ${Q}_{P}^{-1}$ and QS−1 ${Q}_{S}^{-1}$ that QS−1 ${Q}_{S}^{-1}$ have smaller values, less insignificant variation, and weaker correlations with SSEs. Furthermore, QP−1/QS−1 ${Q}_{P}^{-1}/{Q}_{S}^{-1}$ increases concurrent with SSEs. These differences suggest that attenuation is caused by the wave‐induced fluid flow. QP−1/QS−1 ${Q}_{P}^{-1}/{Q}_{S}^{-1}$ could be an important parameter for detecting the presence of fluid. Plain Language Summary: Q−1 ${Q}^{-1}$ value, which represents energy dissipation of seismic wave, is an important parameter for detecting the anelastic heterogeneity in subsurface rocks. However, few observational studies have revealed the characteristics of both P‐ and S‐wave attenuation (QP−1 ${Q}_{P}^{-1}$ and QS−1 ${Q}_{S}^{-1}$, respectively) related to the presence of fluids in the crust and the uppermost mantle. This study reveals that both QP−1 ${Q}_{P}^{-1}$ and QS−1 ${Q}_{S}^{-1}$ show temporal variations associated with the inferred periodic drainage from the upper surface of a subducting slab but QS−1 ${Q}_{S}^{-1}$ is less fluctuated with time. We discuss a possible attenuation mechanism focusing on the differences in the observed QP−1 ${Q}_{P}^{-1}$ and QS−1 ${Q}_{S}^{-1}$ values and propose that the wave‐induced fluid flow (WIFF) may be a dominant control on the increases in attenuation concurrent with the drainage from the megathrust. The obtained results will provide important constraints on attenuation mechanism that is enhanced by the presence of fluid in rocks. Key Points: We estimated the long‐term temporal variations in QP−1 ${Q}_{P}^{-1}$ and QS−1 ${Q}_{S}^{-1}$ at 20–45 Hz above the megathrust boundary of the Philippine Sea PlateBoth QP−1 ${Q}_{P}^{-1}$ and QS−1 ${Q}_{S}^{-1}$ exhibited temporal variations with about 1‐year periodicity and spatiotemporal correlations with slow‐slip eventsSystematic differences between QP−1 ${Q}_{P}^{-1}$ and QS−1 ${Q}_{S}^{-1}$ may provide important constraints on attenuation mechanism enhanced by fluids [ABSTRACT FROM AUTHOR]

In the infrasonic observation of a fumarolic field, distinguishing multiple fumarolic sources is challenging. The array technique effectively estimates the source locations and identifies the target signal from other signals and noise. We conducted an experiment at Kirishima Iwo-Yama, Japan, where two active fumarolic areas were separated by ~ 450 m. A three-element array with an aperture of ~ 20 m was installed between the two fumarolic areas. In addition, a single microphone was installed near one of the fumaroles. The array combined with the waveform correlation analysis estimated the most prominent source but failed to estimate the other weak source. A joint analysis of the array and the single microphone effectively resolved the two sources. It was also confirmed that newly developed power-saving MEMS microphones were useful for observing the fumaroles. This paper presents the instrumentation and analytical method that would be beneficial for monitoring volcanoes that have multiple hydrothermally active vents. [ABSTRACT FROM AUTHOR]

To determine the relationship between muscle stiffness assessed using ultrasound shear wave elastography, spinal motor neuron excitability assessed using the F wave, and clinical findings of spasticity in patients with spastic muscle overactivity following severe traumatic brain injury. This study enrolled 17 inpatients with severe traumatic brain injury and 20 healthy volunteers. Biceps brachii muscle stiffness was then evaluated using ultrasound shear wave speed. Spinal motor neuron excitability was evaluated using the F/M ratio recorded from abductor pollicis brevis muscle. Clinical parameters, such as the modified Ashworth scale and modified Tardieu scale, were assessed in the patient with traumatic brain injury. The patients with traumatic brain injury group had a significantly higher shear wave speed and F/M ratio compared with the healthy group. A higher shear wave speed was correlated with higher clinical spastic severity in patients with traumatic brain injury. The F/M ratio was not significantly correlated with clinical spastic severity. Ultrasound shear wave elastography might be helpful for assessing muscle stiffness in patients with spastic muscle overactivity following severe traumatic brain injury. Further studies comprising larger cohorts are warranted. [ABSTRACT FROM AUTHOR]

Anisotropy within subducted slabs carries important information about the deformation history of the slabs. Seismic waves propagating a long distance within a subducted slab can be utilized to invert for the slab anisotropy. The Dense Ocean Floor Network System (DONET) deployed near the Nankai trough are located in a suitable position to record seismic waves guided along the subducted northern Philippine Sea plate (nPSP). In this study, we perform the shear wave splitting analysis on local event data recorded by ocean bottom seismometers from DONET to measure the anisotropy within the subducting nPSP. The obtained fast axis is sub‐trench‐parallel with inferred strength of 1%–3% anisotropy, arising likely from the fossilized fabric formed during the seafloor spreading period and strengthened by trench‐parallel serpentinized hydrated faults. This result shows that the fossilized anisotropy of nPSP is preserved during the subduction. Plain Language Summary: The geological processes can cause the preferred orientation of anisotropic minerals, resulting in seismic anisotropy. Thus seismic anisotropy beneath a region carries important information about the formation and deformation history of the region. Compared with the anisotropy beneath continents, it remains a challenge to measure the seismic anisotropy beneath oceans, especially within the oceanic lithosphere, due to its relatively thin slab thickness accounting for only a small percentage of the whole seismic ray paths. Here we use seismic data recorded by ocean bottom seismometers (OBSs) deployed near the Nankai trough, where the northern Philippine Sea plate (nPSP) is subducting beneath the Eurasian Plate in the southwest Japan and generating deep earthquakes within nPSP. These OBSs are in a suitable position to detect the seismic waves propagating along the subducting nPSP, which can then be utilized to invert for the anisotropy of nPSP as they avoid the contamination from other structures of the subduction zone. We find that the anisotropy within nPSP may arise from the fossilized fabric during the seafloor spreading and be strengthened by trench‐parallel faults associated with plate bending, and is preserved during the subduction. Key Points: The fast axis of northern Philippine Sea plate (nPSP) is sub‐parallel to the strike of Nankai trough with an inferred 1%–3% anisotropyThe anisotropy within nPSP may be caused by the fossilized fabric, and strengthened by trench‐parallel serpentinized hydrated faultsThe fossilized anisotropy of nPSP related to seafloor spreading is preserved during nPSP subduction [ABSTRACT FROM AUTHOR]

The magnetically coupled three‐phase dual‐active‐bridge (DAB3) DC‐DC converter is highly suitable for high‐power applications. Although the converter has many advantages, the structure, working mode and electromagnetic effect of its key magnetic component—high‐power medium‐frequency three‐phase transformer (MFT3) is more complex, and the capacity, frequency, loss, temperature rise and leakage inductance restrict each other, forming a complex and systematic design problem. This paper focuses on the overall design method and performance of high‐power MFT3. Based on the analysis of steady‐state voltage and current waveforms of DAB3 converter, the expression of harmonic current is derived by using fundamental wave analysis, and the analytical calculation method of copper loss is proposed. According to the piecewise linear flux density waveform excited by six‐step voltage wave, the modified IGSE method is proposed to calculate the core loss. For MFT3 with three‐phase five column core topology, a lumped parameter thermal network model with 14 temperature nodes is established to obtain the temperature rise. The influence of winding arrangement on leakage inductance is analyzed, and the analytical expression of leakage inductance is presented. On this basis, the design method of high‐power MFT3 is proposed based on the free parameter scanning method. A 5 kHz, 15 kW MFT3 model with the nanocrystalline core material is made, and the leakage inductance, core loss, copper loss and temperature rise are extracted by finite element method (FEM) and experiment. The effectiveness of the proposed method is verified by comparing the design results with the FEM simulation and experimental results. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Slip phenomena on plate interfaces reflect the heterogeneous physical properties of the slip plane and, thus, exhibit a wide variety of slip velocities and rupture propagation behaviors. Recent findings on slow earthquakes reveal similarities and differences between slow and regular earthquakes. Episodic tremor and slip (ETS) events, a type of slow earthquake widely observed in subduction zones, likewise show diverse activity. We investigated the growth of 17 ETS events beneath the Kii Peninsula in the Nankai subduction zone, Japan. Analyses of waveform data recorded by a seismic array enabled us to locate tremor hypocenters and estimate the migration patterns and spatial distribution of the energy release of tremor events. Here, we describe three major features in the growth of ETS events. First, independent of their start point and migration pattern, ETS events exhibit patches of high seismic energy release on the up-dip part of the ETS zone, suggesting that the location of these patches is controlled by inherent physical or frictional properties of the plate interface. Second, ETS events usually start outside the high-energy patches, and their final extent depends on whether the patches participate in the rupture. Third, we recognize no size dependence in the initiation phase of ETS events of different sizes with comparable start points. These features demonstrate that the cascading rupture of high-energy patches governs the growth of ETS events, just as the cascading rupture of asperities governs the growth of regular earthquakes. [ABSTRACT FROM AUTHOR]

In recent years, rapid estimation of Peak Ground Motion (PGM) and Modified Mercalli Intensity (MMI) based on a few seconds of the initial portion of P wave has been studied as the most important part of the onsite Earthquake Early Warning (EEW) systems studies. To establish an onsite EEW, we need the empirical relationship between earthquake size, PGM and epicentral distance in real-time mode. In some EEWs, the epicentral distance is estimated from the amplitude growth rate of a few seconds of P waves. Many studies have empirically confirmed that the growth rate becomes smaller as epicentral distance becomes far. This relation is true regardless of the earthquake size. In the current study, five parametric criteria including A, B, B * Pa, B * Pv and B * Pd are proposed for quick detection of destructive oncoming strong motions at a specific target based on ground motions of the first 4 seconds of Japan event waveforms where A and B parameters represent the characteristics of P wave envelope curve in a simple function with the form of Bt. exp(--At). In this study, B parameter is inversely proportional to epicentral distance which can be readily estimated within a given short time after P waves' arrival. Pa, Pv and Pd are the initial peak ground acceleration, velocity and displacement, respectively. The current study represent five thresholds parameters including A, B, B * Pa, B * Pv and B * Pd in order to warn a Peak Ground Velocity (PGV) greater than about 10 cm/sec which are clustered in strong shaking with Modified Mercalli Intensity (MMI) larger than VI. Therefore, destructive earthquakes can be detected form the maximum amplitudes and growth rate of few seconds of P waves by using mentioned parametric criteria. [ABSTRACT FROM AUTHOR]

Automatic and rapid imaging of earthquake rupture process is a difficult task but critical for postearthquake response and possible tsunami early warning. We have developed an automatic system for finite‐fault inversion based on the iterative deconvolution and stacking (IDS) approach, in which we screen the waveforms and update the fault size automatically. Strong‐motion seismograms are used in offline tests to invert for the rupture processes of 34 significant earthquakes in 2008–2017 in and around Japan with magnitudes MW ≥ 6.0 occurred onshore and MW ≥ 6.5 offshore. Rupture model of an earthquake, including moment magnitude, source time function, slip distribution, rupture velocity, and stress drop, is obtained in ~1.5 min on a desktop PC. The moment magnitudes we obtained are consistent with those published by other agencies. The slip distributions, rupture directions, and velocities also agree well with those released by the Japan Meteorological Agency. In all test cases, our results show that the automatic inversion of strong‐motion data can provide reliable major source parameters without manual revision, which demonstrates great potential for emergency response and tsunami early warning purposes. The automatic inversion system developed in this work can also be used to build catalogs of finite‐fault models for moderate to strong earthquakes in other areas where the moment tensor solutions and near‐field waveform data are available. Key Points: We have developed an automatic system for finite‐fault inversion based on the iterative deconvolution and stacking (IDS) techniqueOffline tests demonstrate that the rupture models can be well estimated when the strong‐motion data and the mechanism solution are availableIntegration of the automatic finite‐fault inversion in a rapid response and early warning system is realistic for regions like Japan [ABSTRACT FROM AUTHOR]

Sprint ability develops nonlinearly across childhood and adolescence. However, the underpinning ground reaction force (GRF) production is not fully understood. This study aimed to uncover the kinetic factors that explain these maturation‐related sprint performance differences in Japanese boys and girls. A total of 153 untrained schoolchildren (80 boys, 73 girls) performed two 50‐m maximal effort sprints over a 52‐force‐platform system embedded in an indoor track. Maturity offset (years from peak height velocity; PHV) was estimated using anthropometric data and used to categorise the children into six‐year‐long maturation groups (from group 1 [5.5‐4.5 years before PHV] to group 6 [0.5 years before to 0.5 years after PHV). Maximum and mean step‐averaged velocities across 26 steps were compared across consecutive maturation groups, with further GRF analysis (means and waveforms [statistical parametric mapping]) performed when velocity differences were observed. For boys, higher maximum velocities (effect size ± 90% CI = 1.63 ± 0.69) were observed in maturation group 2 (4.5‐3.5 years before PHV) compared to group 1 (5.5‐4.5 years before PHV), primarily attributable to higher antero‐posterior GRFs across shorter ground contacts. Maximum velocities increased from maturation group 4 (2.5‐1.5 years before PHV) to group 5 (1.5‐0.5 years before PHV) in the girls (effect size ± 90% CI = 1.00 ± 0.78), due to longer ground contacts rather than higher GRFs per se. Waveform analyses revealed more effective reversal of braking forces and higher propulsive forces (e.g. 14%‐77% of stance 4), particularly for comparisons involving boys, which suggested potentially enhanced stretch‐shortening ability. Youth sport practitioners should consider these maturation‐specific alterations when evaluating young athletes' sprint abilities. [ABSTRACT FROM AUTHOR]

We examined the scaling relationships of inland crustal earthquakes occurring in tectonically active regions such as the Japanese Islands. Two important points related to reliable scaling relationships are discussed empirically: the objective estimation of source parameters such as the seismic moment and rupture area, and the regionality of the scaling. Rupture areas are objectively estimated by trimming heterogeneous slip distributions obtained from waveform inversion. Two trimming procedures have been proposed to determine effective rupture areas, by Somerville et al. (Seismol Res Lett 70:59–80, 1999) and Thingbaijam and Mai (Bull Seismol Soc Am 106:1802–1816, 2016). We confirmed that both trimmed rupture areas agree well with each other when applied to the same dataset. The source scaling characteristics are known to depend on the seismotectonic regime. We investigate the source scaling relationships of inland crustal earthquakes in Japan using source parameters obtained from 36 slip models for 22 recent events (Mw 5.4–7.1) by waveform inversion analysis. We confirmed that the source scaling relationships consisting of two stages were almost the same as those obtained for crustal earthquakes on the US West Coast by Hanks and Bakun (Bull Seismol Soc Am 92:1841–1846, 2002). For larger earthquakes (Mw > 7.4) in seismically active regions, Tajima et al. (ZISIN2; J Seismol Soc Jpn 66:31–45, 2013) found saturation of fault displacements showing the third stage. Combining the earthquake data of Mw 5.4–7.1 in this study with those of Mw 7.0–8.0 compiled by Murotani et al. (Pure Appl Geophys 172:1371–1381, 2015), we conclude that the scaling relationship for rupture area versus seismic moment coincides with the three-stage source scaling relationship using source parameters extracted from waveform inversions. [ABSTRACT FROM AUTHOR]

Herein, we present coastal-wave records under historically extreme conditions caused by a strong typhoon in Japan in 2017. The extreme typhoon generated large infragravity waves, reaching a height of 2 m in shallow water. We took advantage of the extraordinary conditions to analyze the effect of the energetic infragravity waves on the nearshore evolution of relatively short waves. Individual wave analyses clearly demonstrate that the instantaneous water-level rise and drawdown caused by the infragravity waves alternately decelerated and accelerated the breaking of short waves under extreme conditions. This mechanism transmitted the large short-wave energy on the infragravity wave crests to the shore, eventually increasing the height of the nearshore waves. This study provides in situ evidence that the infragravity waves significantly affect nearshore wave characteristics under extreme conditions. [ABSTRACT FROM AUTHOR]

We applied advanced surface wave analysis for multichannel and multishot seismic data to estimate S-wave velocity structure with high lateral resolution. Although a horizontally layered structure is typically assumed in surface wave analysis, this assumption might be violated in environments such as geothermal fields because of their heterogeneous geological formation. The lateral variation of phase velocity can be effectively estimated with common midpoint (CMP) cross-correlation (CMPCC) analysis. In this study, we introduced two additional approaches into the CMPCC analysis workflow, to further improve lateral resolution of phase velocity estimates. One approach is window-controlled CMPCC analysis, which applies a spatial window for the CMP gathers while maintaining the accuracy of the phase velocity estimates. In this analysis, we found that it is difficult to improve phase velocity estimates at lower frequencies, as a wider spatial window must be kept to maintain the accuracy of the dispersion curve. Therefore, we introduced another approach in which we consider the direction of surface wave propagation from sources to receivers. Selection of cross-correlations based on source–CMP direction provides a significant improvement in dispersion curve resolution in the presence of lateral velocity variations, for a wide frequency range. We applied direction-controlled CMPCC analysis to seismic data acquired in the Yamagawa geothermal field, Kyushu Island, southwest Japan, and obtained dispersion curves in the heterogeneous geological setting. We then obtained S-wave velocity profiles by applying genetic algorithm inversion to the dispersion curves. The S-wave velocity profiles in the geothermal field resolve shallow and local heterogeneous structures (e.g. volcanic ash, pumice and igneous intrusions) that cannot be identified on reflection seismic profiles. [ABSTRACT FROM AUTHOR]

The 1896 Sanriku earthquake was a typical 'tsunami earthquake' which caused large tsunami despite its weak ground shaking. It occurred along the Japan Trench in the northern tsunami source area of the 2011 Tohoku earthquake where a delayed tsunami generation has been proposed. Hence the relation between the 1896 and 2011 tsunami sources is an important scientific as well as societal issue. The tsunami heights along the northern and central Sanriku coasts from both earthquakes were similar, but the tsunami waveforms at regional distances in Japan were much larger in 2011. Computed tsunamis from the northeastern part of the 2011 tsunami source model roughly reproduced the 1896 tsunami heights on the Sanriku coast, but were much larger than the recorded tsunami waveforms. Both the Sanriku tsunami heights and the waveforms were reproduced by a 200-km × 50-km fault with an average slip of 8 m, with the large (20 m) slip on a 100-km × 25-km asperity. The moment magnitude M of this model is 8.1. During the 2011 Tohoku earthquake, slip on the 1896 asperity (at a depth of 3.5-7 km) was 3-14 m, while the shallower part (depth 0-3.5 km) slipped 20-36 m. Thus the large slips on the plate interface during the 1896 and 2011 earthquakes were complementary. [ABSTRACT FROM AUTHOR]

Volcanic eruptions are sometimes preceded by tilt changes that are an indicator of immediate pre-eruptive processes. In this study, the tilt changes before all monitored eruptions in Japan were surveyed for the first time to address the generality and common features of these signals. An automated procedure was devised to identify tilt changes. The results showed that approximately half of the analyzed eruptions were preceded by tilt changes. Detection ratios depended on station locations, and approximately 10–20% of the total waveforms consisted of detectable tilt changes. Broadband seismic records, when integrated into displacements, showed detection ratios comparable to those of tiltmeter records. The lead times and durations of the tilt changes showed large variations. The durations correlated with amplitudes, although with considerable scatter. Both accelerating and decelerating types of tilt changes were common, and their ratios depended on the volcanoes. These are the first findings on the nature of pre-eruptive tilt changes from many volcanoes, and the waveform analysis procedure proposed in this paper is applicable to other regions. Future works involve extending this study to datasets from other regions, detecting tilt changes from continuous records, applying the proposed method to an early warning system, and detecting longer tilt changes, which require that the proposed approach be improved by subsequent studies. [Display omitted] • All pre-eruptive tilt changes in Japan were systematically surveyed. • Approximately half of the eruptions were preceded by tilt changes. • Broadband seismometers detected tilt changes at rates comparable to tiltmeters. • Durations of the tilt changes weakly correlated with amplitudes [ABSTRACT FROM AUTHOR]

The pseudo point-source model approximates the rupture process on faults with multiple point sources for simulating strong ground motions. A simulation with this point-source model is conducted by combining a simple source spectrum following the omega-square model with a path spectrum, an empirical site amplification factor, and phase characteristics. Realistic waveforms can be synthesized using the empirical site amplification factor and phase models even though the source model is simple. The Kumamoto earthquake occurred on April 16, 2016, with M 7.3. Many strong motions were recorded at stations around the source region. Some records were considered to be affected by the rupture directivity effect. This earthquake was suitable for investigating the applicability of the pseudo point-source model, the current version of which does not consider the rupture directivity effect. Three subevents (point sources) were located on the fault plane, and the parameters of the simulation were determined. The simulated results were compared with the observed records at K-NET and KiK-net stations. It was found that the synthetic Fourier spectra and velocity waveforms generally explained the characteristics of the observed records, except for underestimation in the low frequency range. Troughs in the observed Fourier spectra were also well reproduced by placing multiple subevents near the hypocenter. The underestimation is presumably due to the following two reasons. The first is that the pseudo point-source model targets subevents that generate strong ground motions and does not consider the shallow large slip. The second reason is that the current version of the pseudo point-source model does not consider the rupture directivity effect. Consequently, strong pulses were not reproduced enough at stations northeast of Subevent 3 such as KMM004, where the effect of rupture directivity was significant, while the amplitude was well reproduced at most of the other stations. This result indicates the necessity for improving the pseudo point-source model, by introducing azimuth-dependent corner frequency for example, so that it can incorporate the effect of rupture directivity. [ABSTRACT FROM AUTHOR]

The 2016 Kumamoto earthquake ( Mw 7.0) occurred in the central part of Kyushu Island, southwestern Japan, on April 16, 2016. The mainshock triggered an event of maximum acceleration 700 gal that caused severe damage to infrastructure and thousands of homes. We investigate the source location of the triggered event, and the timing of large energy release, by employing the back-projection method for strong-motion network data. The optimal location is estimated to be [33.2750°, 131.3575°] (latitude, longitude) at a depth of 5 km, which is 80 km northeast of the epicenter of the mainshock. The timing is 33.5 s after the origin time of the mainshock. We also investigate the source mechanism by reproducing observed displacement waveforms at a near-source station. The waveforms at smaller-sized events, convolved with the source time function of a pulse width 1 s, are similar to the signature of the observed waveforms of the triggered event. The observations are also reproduced by synthetic waveforms for a normal-fault mechanism and a normal-fault with strike-slip components at the estimated locations. Although our approach does not constrain the strike direction well, our waveform analysis indicates that the triggered earthquake occurred near the station that observed the strong motions, primarily via a normal-fault mechanism or a normal-fault with strike-slip components. [ABSTRACT FROM AUTHOR]

An Mw7.1 Kumamoto earthquake occurred at 01:25:05 on April 16, 2016 (JST). The earthquake involved a rupture at a shallow depth along a strike-slip fault with surface breaks. Near-fault ground motion records, especially those of a strike-slip earthquake, can provide us with direct information on the earthquake source process. During the earthquake, near-fault seismograms were obtained at KMMH16 station located about 500 m off the fault. The ground displacements were well recovered from the double numerical integration of accelerograms at KMMH16 both on the surface and at the bottom of the 252-m-deep borehole. Fault-parallel static displacement was estimated to be about 1.1 m from the acceleration waveforms. The Dc″ value, which is defined as double the fault-parallel displacement at peak velocity time, was proposed as a proxy of the slip-weakening distance. Using both the velocity and displacement fault-parallel waveforms, the Dc″ value was estimated at about 1 m. This value was between 30 and 50% of the total slip on the fault, which is consistent with previous observations. [ABSTRACT FROM AUTHOR]

The detailed source rupture process of the M 7.3 event (April 16, 2016, 01:25, JST) of the 2016 Kumamoto, Japan, earthquakes was derived from strong-motion waveforms using multiple-time-window linear waveform inversion. Based on the observations of surface ruptures, the spatial distribution of aftershocks, and the geodetic data, a realistic curved fault model was developed for source-process analysis of this event. The seismic moment and maximum slip were estimated as 5.5 × 10 Nm ( M 7.1) and 3.8 m, respectively. The source model of the M 7.3 event had two significant ruptures. One rupture propagated toward the northeastern shallow region at 4 s after rupture initiation and continued with large slips to approximately 16 s. This rupture caused a large slip region 10-30 km northeast of the hypocenter that reached the caldera of Mt. Aso. Another rupture propagated toward the surface from the hypocenter at 2-6 s and then propagated toward the northeast along the near surface at 6-10 s. A comparison with the result of using a single fault plane model demonstrated that the use of the curved fault model led to improved waveform fit at the stations south of the fault. The source process of the M 6.5 event (April 14, 2016, 21:26, JST) was also estimated. In the source model obtained for the M 6.5 event, the seismic moment was 1.7 × 10 Nm ( M 6.1), and the rupture with large slips propagated from the hypocenter to the surface along the north-northeast direction at 1-6 s. The results in this study are consistent with observations of the surface ruptures. [ABSTRACT FROM AUTHOR]

Abnormalities of swallowing in patients with mandibular prognathism have not been evaluated quantitatively. The aim of this study was to compare tongue pressure production for bolus transfer between volunteers with normal occlusion and patients with mandibular prognathism. The control group had 10 female volunteers with normal occlusion, and the patient group had 10 women with mandibular prognathism. Tongue pressure was measured by a palatal sensor sheet at five sites on swallowing 4 mL of a tasteless and odourless jelly. Results: The tongue pressure waveform differed between the control and patient groups. The incidence of a double-peak tongue pressure waveform was more frequent in the patient group. In both groups, the exertion of tongue pressure began at the anterior point of the sensor sheet, followed by the peripheral parts. Although the order of expression of tongue pressure was the same for the two groups, maximum tongue pressure at all parts of the sensor sheet was lower in the patient group than in the control group. Furthermore, swallowing time was longer in the patient group than in the control group at the peripheral parts of the palate. These results clearly show the difference in tongue pressure production during swallowing between patients with mandibular prognathism and volunteers with normal occlusion. The current findings suggest that maxillofacial morphology may affect tongue movement during swallowing. [ABSTRACT FROM AUTHOR]

Mega-thrust earthquakes are anticipated to occur in the Nankai Trough in Southwest Japan. In order to monitor seismicity, crustal deformations, and tsunamis in earthquake source areas, we deployed the seafloor seismic network DONET (Dense Ocean-floor Network System for Earthquakes and Tsunamis) in 2010 (Kaneda et al., 2015; Kawaguchi et al., 2015). The DONET system consists of a total of 20 stations that are composed of multiple types of sensors, including strong-motion seismometers and quartz pressure gauges. These stations are densely distributed at an average distance of 15-20 km and cover from near the trench axis to coastal areas. Observed data are transferred to a land station through a fiber-optic cable and then to the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) data management center through a private network in real time. After the 2011 earthquake off the Pacific coast of Tohoku, each local government close to the Nankai Trough sought to devise a disaster prevention scheme. These local governments requested that JAMSTEC disseminate the DONET data along with other research capabilities so that they could exploit this important earthquake information. In order to provide local government access to the DONET data, which are recorded ostensibly for research purposes, we have developed a web application system, REIS (real-time earthquake information system), that provides seismic waveform data to some local governments close to the Nankai Trough. In the present paper, we introduce the specifications of REIS and its system architecture. [ABSTRACT FROM AUTHOR]

We evaluated nocturnal sleep-wake rhythms and subjective sleep quality on the first postoperative night compared with the preoperative night in 34 patients who had total hip arthroplasty (mean age: 61.9 years; 82.4% female) under spinal anaesthesia. We also examined secondary factors related to sleep disturbances after surgery. Patients wore an accelerometer (actigraph) during the preoperative period and the first postoperative night to track sleep-wake rhythms. Secondary end-points were postsurgical pain and low back pain. Sleep parameters were measured objectively by actigraphy, and subjective sleep quality was measured by the Oguri- Shirakawa-Azumi Sleep Inventory, Middle-Aged and Aged Version and found to worsen significantly after surgery. Actigram data showed a reduction in actual sleep time from 353.7 ± 121.2 min preoperatively to 263.8 ± 104.4 min postoperatively. The data indicate that normalized continuous sleep time is important for patient healing and well-being and that postoperative sleep disturbance is related to low back pain more than to postsurgical pain. [ABSTRACT FROM AUTHOR]

The wave analysis of swallowing sounds has been receiving attention because the recording process is easy and non-invasive. However, up until now, an expert has been needed to visually examine the entire recorded wave to distinguish swallowing from other sounds. The purpose of this study was to establish a methodology to automatically distinguish the sound of swallowing from sound data recorded during a meal in the presence of everyday ambient sound. Seven healthy participants (mean age: 26·7 ± 1·3 years) participated in this study. A laryngeal microphone and a condenser microphone attached to the nostril were used for simultaneous recording. Recoding took place while participants were taking a meal and talking with a conversational partner. Participants were instructed to step on a foot pedal trigger switch when they swallowed, representing self-enumeration of swallowing, and also to achieve six additional noise-making tasks during the meal in a randomised manner. The automated analysis system correctly detected 342 out of the 352 self-enumerated swallowing events (sensitivity: 97·2%) and 479 out of the 503 semblable wave periods of swallowing (specificity: 95·2%). In this study, the automated detection system for swallowing sounds using a nostril microphone was able to detect the swallowing event with high sensitivity and specificity even under the conditions of daily life, thus showing potential utility in the diagnosis or screening of dysphagic patients in future studies. [ABSTRACT FROM AUTHOR]

Conclusions: Mano-videoendoscopy (MVE), a manometry technique with endoscopic confirmation of the pressure catheter, can supplement the information on upper esophageal sphincter (UES) function, and overcomes the drawbacks of videoendoscopic swallowing study (VESS). Objectives: This study aimed to investigate the possibility of replacing videofluorographic swallowing study (VFSS) with MVE, as a test to precisely evaluate UES function. Methods: Data from 52 patients with dysphagia were retrospectively reviewed. All patients underwent both MVE and VFSS for evaluation of dysphagia. The manometry was performed with a transnasally inserted catheter (2.6 mm outer diameter and four pressure sensors) under endoscopic observation. The sensors were kept at the tongue base, upper pyriform sinus, apex of pyriform sinus, and UES. We statistically compared the manometric parameters of UES relaxation with fluorographic UES opening. Results: Fluorographic UES opening was diagnosed as good in 34 patients and poor in 18 patients. The nadir pressure, pressure drop, and pressure rise in the UES had significant correlation on the fluorographic UES opening. Stepwise logistic regression test revealed that pressure drop, the gap between the resting pressure and the nadir of UES pressure, was a robust parameter for predicting fluorographic UES opening, and the cut-off level to anticipate good fluorographic opening was ≥ 33.5 mmHg (specificity, 0.853; sensitivity, 0.759) [ABSTRACT FROM AUTHOR]

Objective: To investigate the effects of the width and cross-sectional shape of the major connectors of maxillary dentures located in the middle area of the palate on the accuracy of phonetic output of consonants using an originally developed speech recognition system. Patients and Methods: Nine adults (4 males and 5 females, aged 24-26 years) with sound dentition were recruited. The following six sounds were considered: [∫i], [t∫i], [ɾi], [ni], [çi], and [ki]. The experimental connectors were fabricated to simulate bars (narrow, 8-mm width) and plates (wide, 20-mm width). Two types of cross-sectional shapes in the sagittal plane were specified: flat and plump edge. The appearance ratio of phonetic segment labels was calculated with the speech recognition system to indicate the accuracy of phonetic output. Statistical analysis was conducted using one-way ANOVA and Tukey's test. Results: The mean appearance ratio of correct labels (MARC) significantly decreased for [ni] with the plump edge (narrow connector) and for [ki] with both the flat and plump edge (wide connectors). For [çi], the MARCs tended to be lower with flat plates. There were no significant differences for the other consonants. Conclusion: The width and cross-sectional shape of the connectors had limited effects on the articulation of consonants at the palate. © 2015 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Highlights: [•] Genetic algorithm and generalized ray theory are used for waveform modeling. [•] A 1-D crustal velocity model in NE Japan is obtained by waveform modeling. [•] Waveforms and later-phase travel times of a local crustal earthquake are used jointly. [•] Travel-time residuals obtained reflect the crustal heterogeneities. [ABSTRACT FROM AUTHOR]

Dispersed P-wave arrivals observed in the subduction zone forearc of Northern Japan suggest that low velocity subducted oceanic crustal waveguide persists to depths of at least 220 km. First arrivals from events at 150–220 km depth show that the velocity contrast of the waveguide reduces with depth. High frequency energy (>2 Hz) is retained and delayed by the low velocity crustal waveguide while the lower frequency energy (<0.5 Hz) travels at faster velocities of the surrounding mantle material. The guided wave energy then decouples from the low velocity crustal waveguide due to the bend of the slab and is seen at the surface 1–2 s after the low frequency arrival. Dispersive P-wave arrivals from WBZ earthquakes at 150–220 km depth are directly compared to synthetic waveforms produced by 2-D and 3-D full waveform finite difference simulations. By comparing both the spectrogram and the velocity spectra of the observed and synthetic waveforms we are able to fully constrain the dispersive waveform, and so directly compare the observed and synthetic waveforms. Using this full waveform modelling approach we are able to tightly constrain the velocity structures that cause the observed guided wave dispersion. Resolution tests using 2-D elastic waveform simulations show that the dispersion can be accounted for by a 6–8 km thick low velocity oceanic crust, with a velocity contrast that varies with depth. The velocities inferred for this variable low velocity oceanic crust can be explained by lawsonite bearing assemblages, and suggest that low velocity minerals may persist to greater depth than previously thought. 2-D simulations are benchmarked to 3-D full waveform simulations and show that the structures inferred by the 2-D approximation produce similar dispersion in 3-D. 2-D viscoelastic simulations show that including elevated attenuation in the mantle wedge can improve the fit of the dispersed waveform. Elevated attenuation in the low velocity layers can however be ruled out. [ABSTRACT FROM AUTHOR]

Abstract: In western Japan, relatively small (M <2) deep low-frequency earthquakes (LFEs) occur at around 30km depth, radiating seismic waves mainly in the frequency band of 2–8Hz. The LFEs are categorized into three types based on their locations: tectonic LFEs on plate boundaries, volcanic LFEs beneath active volcanoes, and isolated intraplate LFEs located far from either plate boundaries or active volcanoes. Despite our lack of understanding of the LFEs, their spatial distributions suggest that tectonic, volcanic, and isolated intraplate LFEs are physically related to interplate megathrust earthquakes, volcanic eruptions, and large inland earthquakes, respectively. The present paper characterizes the seismicity of the three types of LFEs in five regions based on a more complete catalog, thanks to automated event detection and precise relocation using waveform correlation. The results show that isolated intraplate LFEs are more similar to volcanic LFEs than to tectonic LFEs. The volcanic and isolated intraplate LFEs are insensitive to tidal stress, are characterized by power-law magnitude frequency statistics such as the Gutenberg–Richter relation, and are distributed mainly in small vertical clusters, while the tectonic LFEs are modulated by tidal stress, are limited in size, and are distributed along the plate boundary. Hence, we propose that isolated intraplate LFEs should be named “semi-volcanic” LFEs. Since tectonic LFEs and volcanic LFEs are thought to be related to the fluid existence and fluid movements, respectively, isolated intraplate (semi-volcanic) LFEs may be related to crustal fluid movements in the source area. [Copyright &y& Elsevier]

We studied the 11 March 2011 Tohoku tsunami through analysis of the sea level records from 21 tide gauge and 16 DART (Deep-ocean Assessment and Reporting of Tsunamis) stations from across the Pacific Ocean. The extreme power of this trans-oceanic tsunami was indicated by the trough-to-crest heights of 3.03 m at Arena Cove on the western coast of the USA and 3.94 m at Coquimbo on the southern coast of Chile. The average value of the maximum amplitude was 163.9 cm for the examined tide gauge records. At many coastal tide gauge stations the largest wave arrived several hours after the first arrival of the tsunami wave, and the tsunami lasted for a long time with an average duration of 4 days. On the contrary, at most of the DART stations in the deep ocean, the first wave was the largest, the tsunami amplitudes were smaller with an average maximum of 51.2 cm, and the durations were shorter with an average of 2 days. The two dominant tsunami periods on the DART records were 37 and 67.4 min, which are possibly attributed to the width and length of the tsunami source fault, respectively. The dimensions of the tsunami source was estimated as 233 km × 424 km. Wavelet analyses of tide gauge and DART records showed that most of the tsunami energy was distributed at the wide period band of around 10-80 min during the first hour after the tsunami arrival, then it was concentrated in a relatively narrower band. The frequency-time plots showed the switches and lapses of tsunami energy at the 35- and 65-min period bands. [ABSTRACT FROM AUTHOR]

A multiple time window inversion of 53 high-sampling tsunami wave-forms on ocean-bottom pressure, Global Positioning System, coastal wave, and tide gauges shows a temporal and spatial slip distribution during the 2011 Tohoku earthquake. The fault rupture started near the hypocenter and propagated into both deep and shallow parts of the plate interface. A very large slip (approximately 25 m) in the deep part off Miyagi at a location similar to the previous 869 Jogan earthquake model was responsible for the initial rise of tsunami waveforms and the recorded tsunami inundation in the Sendai and Ishinomaki plains. A huge slip, up to 69 m, occurred in the shallow part near the trench axis 3 min after the rupture initiation. This delayed shallow rupture extended for 400 km with more than a 10-m slip, at a location similar to the 1896 Sanriku tsunami earthquake, and was responsible for the peak amplitudes of the tsunami waveforms and the maximum tsunami heights measured on the northern Sanriku coast, 100 km north of the largest slip. The average slip on the entire fault was 9.5 m, and the total seismic moment was 4.2 x 1022 N . m (Mw 9.0). The large horizontal displacement of seafloor slope was responsible for 20%-40% of tsunami amplitudes. The 2011 deep slip alone could reproduce the distribution of the 869 tsunami deposits, indicating that the 869 Jogan earthquake source could be similar to the 2011 earthquake, at least in the deep-plate interface. The large tsunami at the Fukushima nuclear power station is due to either the combination of a deep and shallow slip or a triggering of a shallow slip by a deep slip, which was not accounted for in the previous tsunami-hazard assessments. [ABSTRACT FROM AUTHOR]

Displacement time histories from double-integrated accelerograms typically cannot be used to recover near-field terms because of noise in the acceleration traces. To minimize this problem, empirical mode decomposition (EMD) is used to derive a baseline correction scheme. The scheme is tested against several models composed of a single frequency or two frequencies and offsets in acceleration. It is verified against real displacement time history using Global Positioning Systems (GPS) measurement. For single- and double-frequency-content models, obvious discontinuities are found at drift times for lower intrinsic mode function (IMF) components. A drift model, however, can be clearly found from summing higher IMFs and the residuals of simple frequency-content waveform models. On the other hand, results show that the lesser frequency-content signal has the greater decomposed result. Therefore, a suitable corner frequency for low-pass filtering is first implemented to reduce frequency content. In this case, the trend in the given drift model is easily found by summing higher IMFs for a complex frequency content model (model 3 of this study). A suitable corner frequency for low-pass filtering is attained using a grid-search method. A new semiautomatic EMD-derived baseline correction scheme is tested. The corrected coseismic deformation value (CDV, denoted hereafter as from preevent displacement to the final offset during strong motion), peak ground displacement, and displacement time history from this method have good agreement with 1-Hz continuous GPS measurement for the 2011 Tohoku earthquake. [ABSTRACT FROM AUTHOR]

We studied the scattering properties of high-frequency seismic waves due to the distribution of small-scale velocity fluctuations in the crust and upper mantle beneath Japan based on an analysis of three-component short-period seismograms and comparison with finite difference method (FDM) simulation of seismic wave propagation using various stochastic random velocity fluctuation models. Using a large number of dense High-Sensitivity Seismograph network waveform data of 310 shallow crustal earthquakes, we examined the P-wave energy partition of transverse component (PEPT), which is caused by scattering of the seismic wave in heterogeneous structure, as a function of frequency and hypocentral distances. At distance of less than D = 150 km, the PEPT increases with increasing frequency and is approximately constant in the range of from D = 50 to 150 km. The PEPT was found to increase suddenly at a distance of over D = 150 km and was larger in the high-frequency band (f > 4 Hz). Therefore, strong scattering of P wave may occur around the propagation path (upper crust, lower crust and around Moho discontinuity) of the P-wave first arrival phase at distances of larger than D = 150 km. We also found a regional difference in the PEPT value, whereby the PEPT value is large at the backarc side of northeastern Japan compared with southwestern Japan and the forearc side of northeastern Japan. These PEPT results, which were derived from shallow earthquakes, indicate that the shallow structure of heterogeneity at the backarc side of northeastern Japan is stronger and more complex compared with other areas. These hypotheses, that is, the depth and regional change of small-scale velocity fluctuations, are examined by 3-D FDM simulation using various heterogeneous structure models. By comparing the observed feature of the PEPT with simulation results, we found that strong seismic wave scattering occurs in the lower crust due to relatively higher velocity and stronger heterogeneities compared with that in the upper crust. To explain the observed regional difference, the velocity fluctuation model with 3–4 per cent stronger fluctuation and smaller κ is required at the backarc side of northeastern Japan. [ABSTRACT FROM AUTHOR]

Abstract: Very-long-period (VLP) pulses with widths of 20s on velocity seismograms were observed during volcanic activity at Miyake-jima Volcano, Japan in 2000. The VLP events occurred repeatedly during a few days prior to caldera formation and essentially vanished following the onset of caldera collapse. Waveform inversions of the pulse-like signals point to a source offset 3.5km beneath and 1km south of the summit. A candidate for the source mechanism is the inflation of an elliptical cylinder with axis tilted 20–30° from vertical and major axis of the elliptical cross section oriented northeast-southwest. The inferred mechanism appears consistent with a step-like pressurization of a magma reservoir impacted by a falling rock mass in response to gravitational instability. The repeated occurrences of the rock collapses lead to the caldera formation at Miyake-jima. [Copyright &y& Elsevier]

Abstract: We observed clear PKiKP phases steeply reflected at the inner core boundary (ICB) in seismograms recorded by the dense short-period seismic network on the Japan Islands, and used 119 high-quality waveforms of the PKiKP phases to study the detailed structure of the ICB. The PKiKP phases are observed in seismograms band-pass filtered at 2–3Hz from three deep earthquakes at epicentral distances of 7–20° at 105 seismic stations of High-Sensitivity Seismic Network (Hi-net) on the Japan Islands. After phase weighted stacking, the PKiKP waveforms exhibit some weak but clear phases that appear both before and after the PKiKP arrival, which could be explained by a transition zone with a few thin layers existing in the vicinity of the ICB. We used the reflectivity method to simulate the PKiKP waveforms and adopted a forward modeling approach to determine the optimal multi-layer model. Our results show that 8–17km thick layers with higher density (0.1–1.0%) and higher P-velocity (0.1–1.5%) than the PREM model exist above a sharp ICB, while 10–32km thick layers with lower density (0.4–2.2%) and lower P-velocity (0.4–2.5%) than PREM exist below the ICB. The big jump of density and velocity at ICB in our layered model (0.35–0.43g/cm3, 0.33–0.47km/s) indicates that the ICB itself is still a sharp discontinuity. Our observations of the complex high-frequency PKiKP waveforms suggest that the sharp transition from the outer to inner core may be accompanied by laterally varying layering. The ICB stratification may reflect the gradual solidification process during the growth of the inner core. [Copyright &y& Elsevier]

We investigate the high-frequency content of the initial 50 s of wave-forms from the 2011 Off the Pacific Coast of Tohoku earthquake (Mw 9.0, 11 March 2011). The strong-motion spectra for the Mw 9.0 mainshock are richer in high-frequency (>10 Hz) content than those of the Mw 7.3 foreshock compared to low frequencies. The mainshock spectra are flat up to at least 20 Hz, which is at variance with the general source spectra models such as the ω-square and fmax models. The spectral ratios of the Mw 9.0-7.3 events show that after 20 s from the P-wave arrival time, the high-frequency strong motion of the mainshock is distributed in the southern Tohoku district. Analyses of past moderate magnitude earthquakes (M/w 6.0-7.3) in the area around the mainshock hypocenter indicate that the radiation from the deeper regions is the main cause of the high-frequency strong motion. [ABSTRACT FROM AUTHOR]

Many large earthquakes are preceded by one or more foreshocks, but it is unclear how these foreshocks relate to the nucleation process of the mainshock. On the basis of an earthquake catalog created using a waveform correlation technique, we identified two distinct sequences of foreshocks migrating at rates of 2 to 10 kilometers per day along the trench axis toward the epicenter of the 2011 moment magnitude (Mw) 9.0 Tohoku-Oki earthquake in Japan. The time history of quasi-static slip along the plate interface, based on small repeating earthquakes that were part of the migrating seismicity, suggests that two sequences involved slow-slip transients propagating toward the initial rupture point. The second sequence, which involved large slip rates, may have caused substantial stress loading, prompting the unstable dynamic rupture of the mainshock. [ABSTRACT FROM AUTHOR]

Objective numerical data on swallowing function are needed to aid in eating and swallowing intervention and preventive rehabilitation. Using noninvasive methods, the influences of age and differences in size of water bolus on laryngeal activity and respiratory activity were examined in healthy young and older women. Swallowing function was influenced by age and bolus size. Influence of bolus size was recognized only in duration of laryngeal movement in younger women, with no apparent influence in older women. Results for older women were thought to be related to declines in swallowing function with the physiological aging of respiratory and swallowing muscles. In the future, noninvasive methods need to be developed for evaluating function and therapeutic effects against swallowing function impairment and to provide objective numerical data for health insurers. [ABSTRACT FROM AUTHOR]

Abstract: The Space Environment Research Center of Kyushu University has obtained geomagnetic data in the Circum-pan Pacific Magnetometer Network (CPMN) region for over 10 years, and has recently deployed a new real-time Magnetic Data Acquisition System (MAGDAS) in the CPMN region and an FM-CW radar network along the 210° magnetic meridian (MM) for space weather research and applications. This project intends to get the MAGDAS network fully operational and provide data for studies on space and lithosphere weather. In connection with this project, we propose a new ultra-low frequency (ULF) wave analysis method to study ULF anomalies associated with large earthquakes using magnetic data. From a case study of the 1999/05/12 Kushiro earthquake with magnitude M =6.4, we found a peculiar increase of H-component power ratio A R/A M of Pc 3 magnetic pulsations a few weeks before the earthquake, where A R is the power obtained at Rikubetsu station (r =61km) near the epicenter and A M is the power obtained at a remote reference station, Moshiri (r =205km). It is also found that the H-component power ratio A D/A Y of Pc 3 increased three times just a few weeks before the earthquake and after one week decreased to the normal level, where A D is one-day power at Rikubetsu station and A Y is the one-year-average power. [Copyright &y& Elsevier]

Abstract: We construct fine-scale 3D P- and S-wave velocity structures of the crust and upper mantle beneath the whole Japan Islands with a unified resolution, where the Pacific (PAC) and Philippine Sea (PHS) plates subduct beneath the Eurasian (EUR) plate. We can detect the low-velocity (low-V) oceanic crust of the PAC and PHS plates at their uppermost part beneath almost all the Japan Islands. The depth limit of the imaged oceanic crust varies with the regions. High-VP/VS zones are widely distributed in the lower crust especially beneath the volcanic front, and the high strain rate zones are located at the edge of the extremely high-VP/VS zone; however, VP/VS at the top of the mantle wedge is not so high. Beneath northern Japan, we can image the high-V subducting PAC plate using the tomographic method without any assumption of velocity discontinuities. We also imaged the heterogeneous structure in the PAC plate, such as the low-V zone considered as the old seamount or the highly seismic zone within the double seismic zone where the seismic fault ruptured by the earthquake connects the upper and lower layer of the double seismic zone. Beneath central Japan, thrust-type small repeating earthquakes occur at the boundary between the EUR and PHS plates and are located at the upper part of the low-V layer that is considered to be the oceanic crust of the PHS plate. In addition to the low-V oceanic crust, the subducting high-V PAC plate is clearly imaged to depths of approximately 250 km and the subducting high-V PHS zone to depths of approximately 180 km is considered to be the PHS plate. Beneath southwestern Japan, the iso-depth lines of the Moho discontinuity in the PHS plate derived by the receiver function method divide the upper low-V layer and lower high-V layer of our model at depths of 30–50 km. Beneath Kyushu, the steeply subducting PHS plate is clearly imaged to depths of approximately 250 km with high velocities. The high-VP/VS zone is considered as the lower crust of the EUR plate or the oceanic crust of the PHS plate at depths of 25–35 km and the partially serpentinized mantle wedge of the EUR plate at depths of 30–45 km beneath southwestern Japan. The deep low-frequency nonvolcanic tremors occur at all parts of the high-VP/VS zone—within the zone, the seaward side, and the landward side where the PHS plate encounters the mantle wedge of the EUR plate. We prove that we can objectively obtain the fine-scale 3D structure with simple constraints such as only 1D initial velocity model with no velocity discontinuity. [Copyright &y& Elsevier]