Tomotaka Iwata

• Kyoto University

An M JMA 6.5 crustal earthquake occurred during earthquake swarm activity around the northeastern tip of the Noto Peninsula, central Japan, on May 5, 2023. To elucidate the position of this earthquake in the continuing seismic swarm activity, it is necessary to clarify the relationships between the source rupture process, crustal structure, and the...

On 1 January 2024, a devastating MJ 7.6 earthquake occurred on the Noto Peninsula in Japan. When such a strong earthquake occurs, affected near‐surface soil layers behave nonlinearly and may undergo some structural changes driven by Flow Liquefaction, Cyclic Mobility, or Slow Dynamics phenomena. The structural changes can be manifested by short‐las...

Hallo, M., Asano, K., Iwata, T. (2025). Softening and recovery of near-surface layers during the 2024 M7.6 Noto earthquake, Journal of Geophysical Research: Solid Earth, 130 (4), e2024JB029961. https://doi.org/10.1029/2024JB029961

The M7.6 earthquake that struck the Noto Peninsula on January 1, 2024 had devastating consequences, including the loss of many lives and widespread damage to civil infrastructure. Studying strong motion waveforms of such a destructive event may provide valuable insights into the coseismic dynamic behavior of soil and rock layers. During such earthq...

The site response has its origin in the material properties of the near-surface rock and soil layers. When strong ground motions impinge, the near-surface soils exhibit nonlinear behavior in the stress-strain space and may undergo some structural changes driven by liquefaction or elastic softening phenomena. The structural changes may cause tempora...

Two-way travel time information obtained from autocorrelation function analyses of strong motion waveform data can be used to test and improve velocity structure models of sedimentary basins. The waveform data from strong motion stations in the Kyoto and Nara basins were analyzed in this study. The two-way travel time of SH-wave was estimated from...

Source rupture processes of large earthquakes have been already estimated, for example, by the kinematic source inversion using strong ground motion data recorded during those events, and the effects of the source rupture processes on the generation of strong ground motions have been discussed. Recently, a dynamic source inversion technique has bee...

On 1 January 2024, a devastating M7.6 earthquake occurred on the Noto Peninsula in Japan. Seismic waves were generated on tectonic faults beneath the Noto Peninsula and the Sea of Japan and caused widespread damage to civil infrastructure on the ground surface. In general, the near-surface soil and rock layers cause amplification of seismic waves,...

The earthquake ground motion observed at a site is a result of source, path, and site effects. The site effects can be the origin of casualties and significant damage; hence, they should be investigated especially in urban areas such as Osaka, Kyoto, and Nara basins (Kansai area, Japan). A simple method to investigate the site-specific amplificatio...

In this study, we performed a systematic evaluation of H/V earthquake spectral ratios at 449 sites from the inner Kansai area, which are covered by strong-motion measurements on the ground surface. Our advanced processing of various horizontal components resulted in a database of high-quality H/V spectral curves including the directional dependence...

The long-period strong ground motions with periods above 1 s have, in the case of farther or deeper earthquakes, potential to cause serious damage to structures with low eigen frequency, such as long bridges, oil tanks, or artificially damped structures, such as high-rise buildings. This work focuses on wave propagation due to the deep large earthq...

The Hakodate Plain in the southern part of the Oshima Peninsula, Hokkaido, Japan, is a sedimentary basin surrounded by mountains. The vertical displacements caused by active faults along the western margin of the Hakodate Plain increased the basin depth in the western part of the Hakodate Plain. Small-to-large-sized microtremor array surveys were c...

Strong near-fault ground motions associated with the MJMA 7.3 mainshock of the 2016 Kumamoto, central Kyushu, Japan, earthquake sequence have received attention by seismological and engineering communities. In this study, the kinematic source rupture process was reanalyzed based on an improved approach for the representation of source faults. The s...

To elucidate the spatial variation in period‐dependent seismic radiation for the 2011 Ibaraki‐oki earthquake (Mw 7.9) in Japan, we applied a multiple‐period‐band source inversion approach to near‐source strong‐motion waveforms of this earthquake. We estimated source models of this earthquake in three successive period bands (5–10, 10–25, and 25–50...

The Meinong mainshock (ML6.6) occurred in southern Taiwan at 19:57:26.08 (UTC) on 5 February 2016. To study source characteristics of the mainshock, ground motions of the mainshock are simulated using the empirical Green's function method to construct a strong motion generation area (SMGA) source model. Records of the event occurred on 2 May 2010 (...

Source, propagation path, and site characteristics were separated from strong motion records during the 2016 Kumamoto earthquake sequence using the spectral inversion technique. We evaluated site amplifications from the seismic bedrock to the ground surface for 177 strong motion stations in and around the Kumamoto prefecture. Site amplifications at...

We constructed a three-dimensional (3-D) velocity structure model of the Nara basin, Japan, combining geologic knowledge, geophysical surveys, and seismological observations to contribute to the improvement of ground motion prediction for future earthquakes. Few geophysical surveys have been conducted on the underground structure in the Nara basin....

Abstract The source rupture process of the 2018 Hokkaido Eastern Iburi earthquake (M JMA 6.7) was analyzed by a kinematic waveform inversion method using strong-motion data in 0.04–0.5 Hz. This earthquake occurred close to the Hidaka Collision Zone and the Ishikari depression, where the crustal structure is rather complex. Thus, we used a three-dim...

We constructed a three-dimensional (3-D) subsurface structure model beneath the Wakayama Plain by combining the following three results: (1) the distributions of the depth of the sediment-bedrock interface and P-wave velocity in a sedimentary layer (referred to as Shoubudani Group) were estimated from the seismic reflection survey and the gravity p...

Inter-station cross-correlation functions estimated using continuous ambient noise or microtremor records were used to extract the seismic wave propagation characteristics of the Osaka sedimentary basin, Japan. Temporary continuous observations were conducted at 15 sites in the Osaka basin between 2011 and 2013. The data were analyzed using seismic...

The 2016 Kumamoto earthquake sequence started with an MJMA 6.5 foreshock occurring along the northern part of the Hinagu fault, central Kyushu, Japan, and the MJMA 7.3 mainshock occurred just 28 h after the foreshock. We analyzed the source rupture processes of the foreshock and mainshock by using the kinematic waveform inversion technique on stron...

Many source models for the 2011 Tohoku earthquake are derived by dense observation of teleseismic, strong motion, geodetic, and tsunami open data. We review similarity and difference of source models from strong motion records. Long-period source models in a period range of longer than around 10 s inverted large slip near the hypocenter and along t...

In the estimation of spatiotemporal slip models, kinematic source inversions using Akaike's Bayesian Information Criterion (ABIC) and themultiple-time-windowmethod have often been used. However, there are cases in which conventional ABIC-based source inversions do not work well in the determination of hyperparameters when a non-negative slip constr...

On 2013 April 13, an inland earthquake of Mw 5.8 occurred in Awaji Island, which forms the western boundary of the Osaka sedimentary basin in western Japan. The strong ground motion data were collected from more than 100 stations within the basin and it was found that in the Osaka Plain, the pseudo velocity response spectra at a period of around 6....

Microtremor array observations and single-station microtremor observations are conducted in the Kaga plain and the Ochigata plain, Ishikawa prefecture, Japan, to improve the three-dimensional velocity structure model for strong motion prediction in this area. The lateral variation of the peak periods estimated from the H/V spectra and phase velocit...

In a low-seismicity context, the use of numerical simulations becomes essential due to the lack of representative earthquakes for empirical approaches. The Euroseistest Verification and Validation Project (E2VP) aims at: (a) a quantitative analysis of accuracy of the current, most-advanced numerical methods applied to realistic 3D models of sedimen...

In the two-dimensional discrete element modeling of displacement of sedimentary layers caused by faulting within the basement, we attempted to move a rigid basement as if it were an elastic basement by controlling its motion through application of dislocation solutions. An advantage of our modeling procedure is that we can discuss displacement fiel...

The 2011 Fukushima-ken Hamadori earthquake (MW 6.6) occurred about a month after the 2011 Great Tohoku earthquake (MW 9.0), and it is thought to have been induced by the 2011 Tohoku earthquake. After the 2011 Hamadori earthquake, two subparallel faults (the Itozawa and Yunodake faults) were identified by field surveys. The hypocenter was located ne...

The kinematic source process of the 2011 Off the Pacific Coast of Tohoku earthquake is studied using strong motion data both in low- and high-frequency ranges. The slip distribution is estimated by the waveform inversion analysis using velocity waveforms in the frequency range from 0.01 to 0.125 Hz at strong motion stations along the Pacific coast....

We estimate corner frequencies and stress drops for 298 events ranging from M w 3.2–7.0 in 17 inland crustal earthquake sequences in Japan to investigate the source scaling and variation in stress drops. We obtain the source spectral ratio from observed records by the S-wave coda spectral ratio method. The advantage of using the S-wave coda is in o...

To investigate possible source fault models for the Gifu-Ichinomiya fault, we construct multiple source fault models of the 1891 Nobi earthquake, taking into account several different types of geometry for the Gifu-Ichinomiya fault, and conduct strong ground motion simulations. We choose the most plausible source model by comparing the distribution...

[1] The source-rupture process of the 2011 Ibaraki-oki earthquake was estimated from the joint inversion of the strong-motion and global positioning system (GPS) data. The estimated seismic moment and maximum slip are 7.8 × 1020 Nm (Mw 7.9) and 6.3 m, respectively. The total rupture duration is approximately 30 s. The derived source model has one l...

The source model of the 2011 Tohoku earthquake, which is composed of four strong motion generation areas (SMGAs), is estimated based on the broadband strong ground motion simulations in the frequency range 0.1-10 Hz using the empirical Green's function method. Two strong motion generation areas are identified in the Miyagi-oki region west of the hy...

The source-rupture process during the 2007 Noto Hanto earthquake, which was a reverse-faulting event located near the western coast of the Noto peninsula in central Japan, was estimated by the kinematic linear waveform inversion method. The waveform inversion was conducted by jointly using velocity waveforms recorded at 12 near-source strong-motion...

We present a method for estimating the boundary shape of a 3-D basin velocity structure by waveform inversion, and we apply the method to real seismic data observed in the Osaka sedimentary basin in Japan. The initial model is the 3-D Osaka basin velocity structure model developed by Iwata . (2008. Basin and crustal velocity structure models for th...

We examine the construction methodology of a source model for strong ground-motion prediction of scenario earthquakes with a long active-fault zone including a multi-segment rupture case. For the multi-segment rupture event, different seismic moments are given by applying two different source-model construction methodologies: (1) a methodology base...

We characterize the heterogeneous source slip model of intraslab earthquakes to compare source scaling properties with those of inland crustal and subduction-zone plate-boundary earthquakes. We extracted rupture area (S), total area of asperity (S a), average slip (D) and average slip on asperity (D a) of eleven intraslab earthquakes following the...

At the Ibaraki-ken-oki region where the Paci.c plate subducts beneath the North American plate, repeating M7 class subduction-zone earthquakes have occurred with an interval of approximately 21 years. We estimated the source rupture processes of two M7 Ibaraki-ken-oki earthquakes from broadband strong motion records and compared them to investigate...

Long-period ground motion (period ~2s and longer) observed inside a sedimentary basin has large amplitude, long duration and other interesting ground motion features, reflecting the velocity structure of the basin. Detailed knowledge of the basin structure is necessary to understand and predict long-period ground motion. The boundary of the sedimen...

We studied the effect of the oceanic water layer on strong ground motion simulations. Source faults of subduction zone earthquakes, such as the Nankai-Tonankai earthquake, West Japan, are situated in the offshore area, under a thick water layer. The necessity of including the oceanic water layer in the velocity model for simulations employing the f...

We apply a modified three-dimensional finite difference method to investigate the dynamics of the 1999 Chi-Chi earthquake. We determine the dynamic source rupture process and simulate the strong ground motions over a frequency range of 0.05-0.5 Hz. Our dynamic source model reveals that the rupture process of the Chi-Chi earthquake is much more comp...

Dense strong motion observation networks provided us with valuable data for studying strong motion generation from large earthquakes. From kinematic waveform inversion of seismic data, the slip distribution on the fault surface of large earthquakes is known to be spatially heterogeneous. Because heterogeneities in the slip and stress drop distribut...

We assessed the applicability of the 3-D subsurface velocity structure model of the Osaka sedimentary basin in western Japan for simulations of long-period ground motion (3–20 s) based on two types of long-period ground motion characteristics: (1) strong ground motion from a specific earthquake and (2) site-specific, event-independent horizontal-to...

During the 2007 Noto Hanto earthquake, a K-NET station ISK005, which is located in Anamizu town and approximately 19 km far from the epicenter, recorded the ground velocity larger than 100 cm/s. A set of observational study is carried out to investigate spatial variation of ground motion amplification characteristics in Anamizu town. Firstly, the s...

As long-period ground motion (periods between 2-20s) observed inside basin reflects complicated wave propagation through the basin, precise simulation of long-period ground motion requires a reliable model of the velocity structure of the basin. We propose a method to estimate the three-dimensional (3D) boundary shape of a sedimentary basin by inve...

We develop a new inversion method to obtain the low- and high-frequency wave radiation processes whose border is 1 Hz. In this method, we adopt a consecutive approach to evaluate the fitness between the observed and synthetic strong motions and to synthesize the waveforms. A new feature of our inversion is an evaluation of the fitness of broadband...

We studied the source model and the underground velocity structure model for quantitative estimation of long-period (3-20s) ground motion in the Oita Plain due to a hypothetical Nankai earthquake. First, the deep subsurface velocity structure of the Oita sedimentary basin was validated by a long-period ground motion simulation of the 2000 western T...

The kinematic source rupture process of the 2004 Chuetsu, mid-Niigata prefecture, Japan, earthquake, is estimated from strong-motion data by the linear waveform inversion method. In order to develop appropriate Green's functions, one-dimensional velocity structure models for each station are constructed by modeling the aftershock waveforms. The est...

The long-term occurrence potentials of the megathrust earthquakes in Nankai trough of the subducting Philippine Sea Plate are from 50% and 70% within 30 years from 2008 (The Headquarters for Earthquakes Research Promotion, 2008). The hypothetical source region of Nankai earthquake extends as wide as 300 km in the east-west direction; therefore it i...

Dense strong motion observation networks provided us valuable data for studying strong motion generation from large earthquakes. In recent years, several large earthquakes occurred in Japan, and a large amount of strong motion data is recorded. It is important for advancement of source modeling in scenario-based strong motion prediction to quantify...

We constructed a prototype of the basin and crustal structure model for the Kinki area, southwest of Japan, for the simulation of strong ground motions of hypothetical crustal and subduction earthquakes. We collected results of the deep seismic velocity profiles obtained by the reflection experiments and seismic imaging results, which were conducte...

We studied the applicability of two types of existing three-dimensional (3-D) basin velocity structure models of the Osaka basin, western Japan for long-period ground motion simulations. We synthesized long-period (3–20s) ground motions in the Osaka basin during a M6.5 earthquake that occurred near the hypothetical Tonankai earthquake source area,...

Osaka, the most populated area in western Japan, is located inside a sedimentary basin whose size is approximately 60km x 40km and the maximum bedrock is 3km. As there are many long-period structures such as skyscrapers and oil tanks, it is important to understand long-period ground motion characteristics in this area in order for the reliable pred...

We estimate the source model of the 2005 Miyagi-Oki earthquake, which consists of two source patches called "strong motion generation areas (SMGAs)", to explain the broadband strong motions. The location of the first SMGA is determined from the arrival time differences between the first motion and the first pulse in the P-wave portion. Based on the...

This paper presents seismic response analysis of high-rise buildings subjected to long-period strong ground motions predicted in Kansai area during large earthquakes along the Nankai Trough. Two steel building models, 75m and 150m in height and designed according to common practice in the 1970s early developmental stage in Japan, are prepared to si...

We propose a method to analyze dynamic rupture processes of earthquakes with a dipping fault, using a three-dimensional finite difference (FD) method with nonuniform grid spacing. This approach does not require aligning the fault plane to the FD grid for implementation of the FD method. It can be used to deal with a realistically complex fault geom...

We estimated strong motion generation area (SMGA) source model which is responsible for broadband (0.2, 0.3–10 Hz) strong motions of the 2005 west off Fukuoka prefecture earthquake and its largest aftershock using the empirical Green's function (EGF) method. The estimated SMGAs are almost corresponding to the large slip area deduced by kinematic wa...

A large shallow crustal earthquake occurred at the western off-shore of Fukuoka Prefecture, northern Kyushu, Japan, at 10:53 on March 20, 2005 (JST). Source rupture processes of the mainshock and the largest aftershock on April 20, 2005, are estimated by the kinematic waveform inversion of strong motion seismograms. The rupture of the mainshock sta...

We conduct a systematic and quantitative evaluation of effects of a deep sedimentary structure model between the engineering and seismic basements on the theoretical broadband site-amplification spectra, taking sites in the Osaka basin, Japan, as a test site. First, from a parametric study on theoretical evaluation of site amplification, adopting a...

This article reviews studies on ground motion characteristics during the 2004 earthquake sequence off the Kii peninsula and the Tokai district occurred on September 5. Long-period ground motions are observed at stations in the large sedimentary basins such as Kanto, Nobi, and Osaka. Typical predominant periods of ground motions at each basin are ap...

We estimated the source model for the foreshock of the 2004 off the Kii peninsula earthquakes by empirical Green's function modeling. The size and the rise time of the strong motion generation area (SMGA) were estimated to be 30 × 15 km, and 0.9 sec, respectively. The stress drop of the SMGA was calculated to be 8.3 MPa. This model could reproduce...

Long-period (5–20 s) ground motion simulations in the Kinki area during the M J 7.1 foreshock of the 2004 off the Kii peninsula earthquakes are performed. We construct a three-dimensional underground structure model that includes the source region and Osaka basin area to confirm propagation-path effects of crustal structure on long-period ground mo...

Synopsis It is essential for disaster prevention to quantify the earthquake vulnerability of urban infrastructures in consideration of their life cycle. As part of a five-year study on this subject, presented in this article are: the refinement of prediction of strong motions, examinations into actual performance of nonstructural components, ration...

A large intraslab earthquake (MJMA 7.1) with the focal depth of about 70km occurred in the Pacific slab below off Miyagi Prefecture, northeastern Japan on May 26, 2003. This earthquake source brought strong high-frequency ground motion to the near-source region. At first, a source model is estimated by the forward modeling through strong motion sim...

A characterized source model (Irikura and Miyake, 2001; Miyake et al., 2003) for strong ground motion prediction is constructed with the heterogeneous source slip distribution results of the kinematic source inversion. For ground motion simulation, high-frequency radiation level should be constrained. Irikura et al. (2004) give stress drop on the a...

SUMMARY Several differences of observed ground motion characteristics between crustal and intraslab earthquakes seem to be caused by not only propagation-path but also source characteristics. We studied the characterization of source models for shallow intraslab earthquakes based on strong motion simulations. Appropriate source models of several sh...

The dynamic rupture process of the Chi-Chi earthquake has been investigated based on a 3-D spontaneous shear crack model, using a thick fault zone model and a slip-weakening friction law. Our results show that the dynamic rupture process of this event is very complex. The distribution of the rupture starting time is much more inhomogeneous than tha...

The 1999 Chi-Chi, Taiwan earthquake, M W = 7.6, caused severe damage in the near-fault region of the earthquake. In order to evaluate site effects in the near-field strong motions we estimate S-wave velocity structures of sediments at four sites using array records of microtremors. We also recalculated S-wave velocity structures at other four sites...

We estimate strong motion generation areas that reproduce near-source ground motions in a broadband frequency range (0.2–10 Hz) using the empirical Green's function technique. The strong motion generation areas are defined as ex-tended areas with relatively large slip velocities within a total rupture area. Four M 6 class (the 1997 Kagoshima on Mar...

SUMMARY From recent development of the waveform inversion analyses for estimating rupture process using strong motion data during large earthquakes, we have understood that strong ground motion is relevant to slip heterogeneity inside the source rather than average slip in the entire rupture area. Asperities are characterized as regions that have l...

Synopsis We developed the crustal structure model from the source region of the Nankai trough to the Osaka basin in Kinki area for ground motion modeling by comparing observed records and simulated long-period (>2s) ground motions using finite difference method. We examined the records of an intermediate-size event (MW4.3) and the largest aftershoc...

To estimate appropriate source model for the prediction of strong ground motion for the intermediate period range around 1s, we should use more sophisticated, modified structure model for calculation of the Green's functions. Here, waveform inversion is performed for the slip model of the 2000 Tottori-ken Seibu earthquake for the intermediate perio...

Source modeling of recent shallow intraslab earthquakes is studied using strong-motion data. The total area of strong-motion generation areas obtained is smaller than the prediction from the empirical relationship for inland crustal earthquakes by Somerville and co-workers. Moreover, the ratio between the combined area of strong-motion generation a...

To estimate source model, appropriate for the intermediate period range around 1s, we should use more sofisticated, modified velocity structure model for calculations of the Green's functions. Here, waveform inversion is performed for slip model of the 1997 Kagoshima-ken Hokuseibu earthquake in the intermediate period range using structure model ad...

The Oubaku fault is an active fault bounding the south-eastern edge of the Kyoto Basin. Although the structure of the fault was inferred to be reverse by the past several reports, the vertical displacement of it has remained unknown and the inferred strikes have been different author by author especially in and around Gokasho, Uji. In order to know...

In order to obtain knowledge concerning the physics of earthquake rupturing more precisely and to obtain reliable source process for near-source ground motion simulation, we introduced a convolution method that incorporates the effect of a moving dislocation over a rectangular area to a synthetic point source into computing the element source waves...

Strong motion generation areas which reproduce ground motions in 0.2 to 10Hz were estimated using the empirical Green's function method. This strong motion generation area was somewhat smaller than the total rupture area, and coincident with the area of asperities derived from heterogeneous slip distributions estimated by waveform inversions using...

The source geometry and slip distribution at rupture termination of the 1995 Hyogo-ken Nanbu earthquake were investigated using waveform inversion on the assumption of fault branching in the northeastern part of the rupture model. Possible branching of the Okamoto fault is suggested both by the static-displacement distribution and damage extension...

In 1997, two magnitude 6 class earthquakes occurred in the northwestern part of Kagoshima prefecture in Japan. One of them occurred on March 26 (MJMA6.5) and the other on May 13 (MJMA6.3). We examined the source models of these two events using the observed seismograms by K-NET at four stations surrounding the source areas. We proposed an objective...

We investigate the characteristics of the stress field associated with the 1995 Hyogo-ken Nanbu (Kobe) earthquake. We use for the study a tomographic model of the fault slip inferred from the numerous near-field recordings, and we calculate the space and time evolution of shear stress on the fault during the earthquake. We show that the spatial dis...

We model the ground motion from an aftershock of the 1995 January 17 Hyogo-ken Nanbu (Kobe) earthquake to investigate basin edge effects on wave propagation in Higashinada ward, downtown Kobe. Point-source finite-difference seismograms calculated using a double-couple solution and a 2-D basin structure are compared with the ground-motion velocity s...

We extend a new waveform inversion scheme (Aoi et al., 1995) for estimating underground structure with an irregular-shaped basement as a target to cases where plane waves with an arbitrary azimuth impinge on the structure, i.e., from a direction not necessarily perpendicular to the major axis of the structure. We proved the validity of this scheme...

We constrained the location of faulting beneath Kobe during the 1995 Hyogo-ken Nanbu (Kobe), Japan, earthquake by investigating the particle motion of strong motion records from sites close to the causative fault. The intersection of the earth's surface and the extension of buried fault plane is consistent with known active fault lines but not with...

Site amplifications during aftershocks of the 1995 Hyogo-ken Nanbu earthquake were examined in and around the disaster area of Higashinada ward, Kobe City, Japan. Five temporary stations together with the KOB station (CEORKA) were installed just after the main shock to arrange an array for strong ground motion observations across a severe damage ba...

We estimated the source process of the 1995 Hyogo-ken Nanbu (Kobe), Japan, earthquake based on: 1) locating buried fault planes in the Kobe area by examining particle motion at observation stations in the near-source area and 2) multi-time window linear waveform inversion of strong ground motion seismograms. S-wave particle motion diagrams created...

Ground motion records from aftershocks of the January 17, 1995, Hyogo-ken Nanbu earthquake provide a good opportunity for evaluating the Osaka basin edge effects on wave propagation in the Kobe area. Aftershock ground motion recorded in a small array deployed at sites within outside the heavily damaged zone, east of Kobe City, show very large ampli...

We propose a new method to estimate site amplification effects at specific sites, separating source and propagation-path effects. First, we calculate “specified spectra” from a given source and propagation-path effects, with a fixed site effect of 2.0. Then, we include effects of rupture process into the “specified spectra” using the empirical Gree...

The paper describes a method for estimating the boundary shape of a basin structure using seismograms observed on the surface. With this waveform inversion scheme, an accurate estimation is possible with data from a few surface stations, because seismic waves are affected not only by the local structure beneath the observation station but also by t...

Well-developed basin-induced waves with a predominant frequency of about 0.3 Hz were detected as later arrivals of a direct S-wave in seismograms observed in the Osaka basin, western Honshu from three deep earthquakes occurring near Japan. The wave type and the secondary source area of the basin-induced waves were examined using a semblance techniq...

We develop a method to determine the boundary shape of basin structures using seismograms observed on the surface through a waveform inversion scheme. Our method is based on the fact that seismic waves observed at stations on the surface are affected not only by the local structure beneath the observation point but also by the whole basin structure...

The fault plane model was constructed and the rupture process of the 1945 Mikawa earthquake (M=6.8) was determined from strong motion records. To date, two fault plane models have been reported, one of which uses geodetic data and the other the aftershock distribution. The fault plane model presented here is a thrust that strikes NNW-SSE with a sma...

Shallow subsurface structure around Hino River in the south-east shore of Lake Biwa was investigated by means of seismic reflection survey. The target area on the western margin of a seismic quiescent zone between the lake and the Suzuka range includes a belt of steep gradient of Bouguer anomaly which inclines west. Survey lines were designed, one...

We developed an inverse Radon-transform method to reconstruct slip velocity intensity (SVI) on the fault plane by using near-field seismograms. The observed source time function is approximated to the integration of the product of the SVI and the isochrone velocity along the isochrone, the shape of which depends on the fault plane-observation point...

Effects of surface geology on seismic motions are investigated using observed seismograms by an array across the Kyoto basin extending from the rock outcrop near the eastern margin to the center. By a comparison with low-pass-filtered seismograms in the basin sites, the spatial wave-form variation and elongation of duration of the S-wave portion (f...