Yuji Yagi

University of Tsukuba

Conventional seismic source inversion estimates the earthquake rupture process on an assumed fault plane that is determined a priori. It has been a difficult challenge to obtain the fault geometry together with the rupture process by seismic source inversion because of the nonlinearity of the inversion technique. In this study, we propose an invers...

How does fault slip follow an earthquake rupture front propagating faster than the local shear-wave velocity (i.e., at supershear speed)? How does a supershear rupture front pass through a geometrically complex fault system? Resolving the evolution of such complex earthquake ruptures is fundamental to our understanding of earthquake-source physics,...

How an earthquake rupture propagates strongly influences the potentially destructive ground shaking. Complex ruptures often involve slip along multiple faults, which masks information on the frictional behaviour of fault zones. Geometrically smooth ocean transform fault plate boundaries offer a favourable environment to study fault dynamics, becaus...

The September 28 2018 Palu tsunami surprised the scientific community, as neither the earthquake magnitude nor its strike-slip mechanism were deemed capable of producing the wave heights that were observed. However, recent research has shown that the earthquake generated several landslides inside Palu bay. The authors conducted a post-disaster fiel...

Conventional seismic source inversion estimates the earthquake rupture process on an assumed fault plane that is determined a priori. It has been a difficult challenge to obtain the fault geometry together with the rupture process by seismic source inversion because of the nonlinearity of the inversion technique. In this study, we propose an invers...

How does fault slip follow an earthquake rupture front propagating faster than the local shear-wave velocity (i.e., at supershear speed)? How does a supershear rupture front pass through a geometrically complex fault system? Resolving the evolution of such complex earthquake ruptures is fundamental to our understanding of earthquake-source physics,...

Teleseismic waveforms contain information on fault slip evolution during an earthquake, as well as on the fault geometry. A linear finite-fault inversion method is a tool for solving the slip-rate function distribution under an assumption of fault geometry as a single or multiple- fault-plane model. An inappropriate assumption of fault geometry wou...

Rupture propagation of an earthquake strongly influences potentially destructive ground shaking. Variable rupture behaviour is often caused by complex fault geometries, masking information on fundamental frictional properties. Geometrically smoother ocean transform fault (OTF) plate boundaries offer a favourable environment to study fault zone dyna...

Waveform backprojection (BP) is a key technique of earthquake-source imaging, which has been widely used for extracting information of earthquake source evolution that cannot be obtained by kinematic source inversion. The technique enjoys considerable popularity, owing to the simplicity of its implementation and the robustness of its processing, bu...

Teleseismic waveforms contain information on fault slip evolution during an earthquake, as well as on the fault geometry. A linear finite-fault inversion method is a tool for solving the slip-rate function distribution under an assumption of fault geometry as a single or multiple-fault-plane model. An inappropriate assumption of fault geometry woul...

We investigated the foreshock activity characteristics using the Japan Meteorological Agency Unified Earthquake Catalog for the last 20 years. Using the nearest-neighbor distance approach, we systematically and objectively classified the earthquakes into clustered and background seismicity. We further categorized the clustered events into foreshock...

The last earthquake that affected the city of Coquimbo took place in September 2015 and had a magnitude of Mw = 8.3, resulting in localized damage in low-lying areas of the city. In addition, another seismic gap north of the 2015 earthquake rupture area has been identified; therefore, a significant earthquake (Mw = 8.2 to 8.5) and tsunami could occ...

Waveform backprojection is a key technique of earthquake-source imaging, which has been widely used for extracting information of earthquake source evolution that cannot be obtained by kinematic source inversion. The technique enjoys considerable popularity, owing to the simplicity of its implementation and the robustness of its processing, but the...

Geometric discontinuities within fault systems known as geometric barriers contribute to irregular rupture evolutions during earthquakes. We applied a hybrid backprojection method to high-frequency teleseismic P-waveforms to investigate the role of geometric barriers in the rupture propagation during the MW 7.9 2008 Wenchuan, China, earthquake. We...

Previous research revealed a dynamically triggered earthquake front propagating along Southwest Japan, in correlation with the arrival of surface waves from the 2011 M9.0 Tohoku-oki earthquake. However, some characteristics of the dynamically initiated seismic activation have not been investigated in detail. We analyse first the dynamic triggering...

A seismic source model for the MW 8.1 2017 Chiapas, Mexico, earthquake was constructed by kinematic waveform inversion using globally observed teleseismic waveforms, suggesting that the earthquake was a normal-faulting event on a steeply dipping plane, with the major slip concentrated around a relatively shallow depth of 28 km. The modeled rupture...

A seismic source model for the Mw 8.1 2017 Chiapas, Mexico, earthquake was constructed by kinematic waveform inversion using globally observed teleseismic waveforms, suggesting that the earthquake was a normal-faulting event on a steeply dipping plane, with the major slip concentrated around a relatively shallow depth of 28 km. The modeled rupture...

The last earthquake which affected Coquimbo city took place in September 2015, with localized damage observed in low areas of the city. In addition, another seismic gap north of the 2015 earthquake rupture area has been identified; therefore, a significant earthquake and tsunami could occur in the near future. The present paper develops the tsunami...

As high-resolution observational data become more common, the demand for numerical simulations of crustal deformation using 3-D high-fidelity modelling is increasing. To increase the efficiency of performing numerical simulations with high computation costs, we developed a fast solver using heterogeneous computing, with graphics processing units (G...

We constructed a seismic source model for the 2015 MW 8.3 Illapel, Chile earthquake, which was carried out with the kinematic waveform inversion method adopting a novel inversion formulation that takes into account the uncertainty in the Green’s function, together with the hybrid backprojection method enabling us to track the spatiotemporal distrib...

On September 16, 2015 a magnitude Mw 8.3 earthquake took place off the coast of the Coquimbo Region, Chile. Three tsunami survey teams covered approximately 700 km of the Pacific coast. The teams surveyed the area, recording 83 tsunami flow depth and runup measurements. The maximum runup was found to be 10.8 m at only one small bay, in front of the...

We discuss the theoretical estimation of co-seismic energy release with respect to a random spatial distribution of stress drop, which is an extension of conventional stress drop modelling. For slip distributions characterised by the von Kármán-type power spectral density, we examine the dependence of the estimated energy release on the upper limit...

We estimated moment tensor and centroid depth of eight small/moderate local earthquakes occurred between 2011 and 2013 in the northern Red Sea Triple Junction using a moment tensor inversion of near-source waveform data recorded by very broadband stations of the Egyptian National Seismic Network (ENSN). We also estimated the focal mechanism using t...

In 2013, a large deep earthquake occurred at the sea of Okhotsk. Some researchers have indicated the complex rupture process of this earthquake. However, there is still a lack of information about the rupture process, especially obtained by a high frequency analysis. Thus, we investigated the precise source process of the 2013 Sea of Okhotsk deep e...

The MJMA7.3 Kumamoto earthquake occurred on April 16, 2016, in the western part of Kyushu, at a depth of 12 km, on an active strike-slip fault. Here, we report on a relatively widespread activation of small remote earthquakes, which occurred as far as Hokkaido, detected by analyzing the continuous waveform data recorded at seismic stations all over...

We resolve the density structure of a possible magma reservoir beneath Aso, an active volcano on Kyushu Island, Japan, by inverting gravity data. In the context of the resolved structure, we discuss the relationship between the fault rupture of the 2016 Kumamoto earthquake and Aso volcano. Low-density bodies were resolved beneath central Aso volcan...

The temporal epidemic-type aftershock sequence (ETAS) model is widely used to describe seismicity. However, only a few programs for estimation of the temporal ETAS model parameters are publicly available, and it is difficult to routinely apply some of them to observed data, due to initial value dependence. A robust temporal ETAS estimation program...

We constructed the rupture process model for the 2016 Kumamoto, Japan, earthquake from broadband teleseismic body waveforms (P-waves) by using a novel waveform inversion method that takes into account the uncertainty of Green's function. The estimated source parameters are: seismic moment = 5.1 texttimes 1019 Nm (Mw = 7.1), fault length = 40 km, an...

During the last decades, major tsunamigenic events as Mw 9.2 Sumatra – Andaman, 2004, Mw 8.8 Maule, Chile and Mw 9.0 Tohoku – Oki, Japan have provided valuable information to the scientific community about predominant processes in the generation, propagation and impact of a tsunami on far and near – field coastal zones. In this context, new insight...

Finite-fault earthquake source inversions infer the (time-dependent) displacement on the rupture surface from geophysical data. The resulting earthquake source models document the complexity of the rupture process. However, multiple source models for the same earthquake, obtained by different research teams, often exhibit remarkable dissimilarities...

In this study, an integrated multi-channel analysis of Surface Waves (MASW) technique is applied to explore the geotechnical parameters of subsurface layers at the Zafarana wind farm. Moreover, a seismic hazard procedure based on the extended deterministic technique is used to estimate the seismic hazard load for the investigated area. The study ar...

We constructed a seismic source model for the 2015 M W 8.3 Illapel, Chile earthquake, which was carried out with the kinematic waveform inversion method adopting a novel inversion formulation that takes into account the uncertainty in the Green’s function, together with the hybrid backprojection method enabling us to track the spatiotemporal distri...

On September 16, 2015 a magnitude Mw 8.3 earthquake took place off the coast of the Coquimbo Region, Chile. Three tsunami survey teams covered approximately 700 km of the Pacific coast. The teams surveyed the area, recording 83 tsunami flow depth and runup measurements. The maximum runup was found to be 10.8 m at only one small bay, in front of the...

The 2015 Mw 7.8 Nepal-Gorkha earthquake with casualties of over 9,000 people was the most devastating disaster to strike Nepal since the 1934 Nepal-Bihar earthquake. Its rupture process was imaged by teleseismic back-projections (BP) of seismograms recorded by three, large regional networks in Australia, North America and Europe. The source images...

Tsunami inundation maps are a powerful tool to design evacuation plans of coastal communities, additionally can be used as a guide to territorial planning and assessment of structural damages in port facilities and critical infrastructure (Borrero et al., 2003; Barberopoulou et al., 2011; Power et al., 2012; Mueller et al., 2015). The accuracy of i...

A few low-angle normal fault earthquakes at approximately the depth of the plate interface, with a strike nearly parallel to the trench axis, were detected immediately after the 2011 Tohoku-oki earthquake. After that, however, no such normal fault events have been observed until the occurrence of the 2014 MW 6.6 Fukushima-oki earthquake. Here we an...

We compared spatiotemporal slip-rate and high-frequency (around 1 Hz) radiation distributions from teleseismic P wave data to infer the seismic rupture process of the 2015 Gorkha, Nepal, earthquake. For these estimates, we applied a novel waveform inversion formulation that mitigates the effect of Green's functions uncertainty and a hybrid backproj...

Seismic Energy ES gives a minimum of strain energy drop defined as an inner product of spacial distribution of coseismic slip and stress change on a fault surface (Andrews 1978 JGR). Traditionally, ES has been obtained by multiplying mean stress drop and seismic moment divided by the rigidity by assuming the distribution of stress drop is constant...

On April 1, 2014 a great thrust earthquake (Mw 8.1) occurred off Iquique, northern Chile. A remarkable foreshock sequence was observed about 2 weeks before the mainshock. Seismic source models are essentially important to reveal the relationship between the mainshock and foreshock activity. However, seismic source models for the Iquique earthquake...

High-frequency seismic waves are generated by abrupt changes of rupture velocity and slip-rate during an earthquake. Therefore, analysis of high-frequency waves is crucial to understanding the dynamic rupture process. Here, we developed a hybrid back-projection method that considers variations in focal mechanisms by introducing a non-planar fault m...

The dynamic triggering of earthquakes is well documented, however the underlying physical mechanisms remain obscure. Here we analyze the seismicity in Northern Nagano, central Japan, following the Tohoku-oki quake, until the occurrence 13 h later of an Mw6.2 local earthquake. We use waveform-detection techniques to identify 17 times more earthquake...

The rupture process of the 2014 Iquique, Chile earthquake is inverted from teleseismic P-wave data applying a novel formulation that takes into account the uncertainty of Green's function, which has been a major error source in waveform inversion. The estimated seismic moment is 1.5 × 1021 Nm (Mw =8.1), associated with a 140 km long and 140 km wide...

We demonstrate our ABIC inversion scheme by inverting InSAR displacements and teleseismic waveform data for the 1997 Manyi, Tibet, earthquake. We test, using a simplified fault geometry, three cases-InSAR data inverted alone, vertical component teleseismic broad-band waveform data inverted alone and a joint inversion of both data sets. The InSAR-on...

We clarified the theoretical relationship between the back-projection (BP) imaging and classical linear inverse solutions via the hybrid back-projection (HBP) imaging. In the HBP imaging, which is mathematically similar to the time-reversal source imaging, cross correlations of observed waveforms with the corresponding Green's functions are calcula...

The September 2, 2009 Tasikmalaya, West Java earthquake was a quite unique earthquake. The source mechanism of this event is not consistent with the characteristic of the tectonic stress in this region in which the strike direction in general parallels to the present-day trench. In fact, the strike of the September 2, 2009 Tasikmalaya earthquake is...

In order to enhance our understanding of the earthquake mechanism and seismotectonic characteristics of the September 2, 2009 Tasikmalaya earthquake, we have performed the joint inversion method to the near field data from the MCGA regional network and teleseismic body wave data from the IRIS-DMC seismic network. To make the stable inversion, we ad...

The 2011 Tohoku earthquake demonstrated that extremely large seismic slip can occur at shallow plate interfaces in subduction zones. The large slip area for the Tohoku earthquake included the source region of a tsunami earthquake. We performed dynamic rupture simulations using simplified fault models and the mechanism of thermal fluid pressurizatio...

The back-projection (BP) method has become a popular tool to image the rupture process of large earthquakes since the success of Ishii et al. (2005), while it has not been clear what the BP image represents physically. We clarified the theoretical background of the back-projection (BP) imaging and related it to classical inverse solutions via the h...

A sequence of M7-class interplate earthquakes (M6.7-7.3) occurred from 2003 to 2011 before the occurrence of the M9 2011 Tohoku-oki earthquake. To investigate the relationship between these previous events and the giant earthquake, we determined the source processes of these events by joint inversion method. We performed the inversions by using bot...

From the comparison of observed 1-Hz GPS data with simple forward computation that evaluates near and intermediate field terms, we put constraints on the early-stage rupture process of the 2011 Tohoku-oki earthquake. Mainly based on the time difference of the onset of large eastward displacements at stations along the northern coast of the source r...

We developed a new back-projection method that uses teleseismic P-waveforms to integrate the direct P-phase with reflected phases from structural discontinuities near the source and used it to estimate the spatiotemporal distribution of the seismic energy release of the 2011 Tohoku-oki earthquake. We projected a normalized cross-correlation of obse...

We have estimated the spatio-temporal slip distribution of the 12 May, 2008, Wenchuan earthquake from teleseismic P-wave data. Teleseismic body wave observations are useful geophysical observations for estimating the overall seismic source process immediately after a great earthquake. However, it is difficult to constrain the slip vectors of later...

The Tohoku-oki earthquake resulted in substantial slip relatively near the coast from Miyagi to Ibaraki prefectures as well as extremely large slip near the trench. The moment-rate function has a shoulder around s and a large peak about s. The former corresponds to a significant moment release in the source area of the Miyagi-oki earthquake, and th...

We investigated the source process of the 2010 Mentawai earthquake by joint inversion method using near source and teleseismic body-wave data. To perform a stable inversion, we applied smoothing constraints and determined their relative weights on the observed data using ABIC criterion. The teleseismic waveforms were windowed for 150 sec, band-pass...

On 11 March 2011, the Tohoku-oki earthquake in eastern Japan and the devastating tsunami that followed it caused severe damage and numerous deaths. To clarify the rupture process of the earthquake, we inverted teleseismic P-wave data applying a novel formulation that takes into account the uncertainty of Green's function, which has been a major err...

The devastating 2011 Tohoku earthquake was observed by dense networks of geophysical instruments. A unified source model was constructed through joint inversion of teleseismic, strong motion, and geodetic datasets. The result indicates that the earthquake consists of three main ruptures. After small rupture in the initial 50 s, the first rupture ex...

We estimated the spatial and temporal slip distribution for the 27 February 2010 Maule earthquake from teleseismic body wave data. To obtain a stable inversion solution, we used the data covariance matrix from the observation and modeling errors, incorporated smoothing constraints and determined their optimal values by using the Akaike Bayesian Inf...

In principle, we can never know the true Green's function, which is a major error source in seismic waveform inversion. So far, many studies have devoted their efforts to obtain a Green's function as precise as possible. In this study, we propose a new strategy to cope with this problem. That is to say, we introduce uncertainty of Green's function...

Explaining deep seismicity is a long-standing challenge in earth science. Between 300 and 700 km depth, earthquakes are scarce except between ∼530 and ∼600 km, where the majority of events occur. By imaging the seismic rupture process for a set of recent deep earthquakes using the back projection of teleseismic P-waves, we found that the rupture ve...

We constructed a program set for estimating moment tensor solutions using near source seismograms. We take the effect of the source time function into account, which has been neglected in predominant program sets of the moment tensor analysis with near source seismograms. In our program set, we approximate the horizontal location of the centroid to...

Explaining deep seismicity is a long-standing challenge in earth science. Deeper than 300 km, the occurrence rate of earthquakes with depth remains at a low level until ~530 km depth, then rises until ~600 km, finally terminate near 700 km. Given the difficulty of estimating fracture properties and observing the stress field in the mantle transitio...

In the finite fault source inversion, seismic source area has usually been approximated by simple fault plane model for simplicity. This approximation, however, may generate the correlated modeling errors originated from the focal mechanism variation in a rupture process, which contributed to biased results in the seismic waveform analysis. This ef...

For evaluating the deformations of the Earth’s crust in the Northern Tien Shan, we calculated the mode and intensity of the seismotectonic deformations (STD) for this region. The input for these calculations were the catalog data on the focal mechanisms of earthquakes, obtained by wave inversion of the signals recorded at the Kyrgyz seismic network...

http://www.tulips.tsukuba.ac.jp/mylimedio/dl/page.do?issueid=1046783&tocid=100091690&page=3-4

1. Introduction On September 11, 2008, a large thrust earthquake with magnitude (JMA) of 7.1 occurred off Tokachi, southeastern Hokkaido, Japan, located near hypocenter of the giant 1952 and 2003 Off-Tokachi earthquakes. It should be noted that the very-low frequency (VLF) earthquakes were detected in/around source area of 2008 event. To understand...

We evaluated the quality of the local seismic waveform recorded at Yasawa station established by the Mineral Resources Department (MRD, Fiji), and tried to estimate moment tensor solution by using this waveform data. We also estimated moment tensor solution and seismic source process by using teleseismic body wave so as to investigate the faulting...

The IISEE started a project to determine the following earthquake information for large (Mw>=7.2) earthquakes in the world between 1994 and October, 2004 by the analytical techniques developed by the IISEE staff members and visiting researchers: centroid moment tensors, aftershock distributions, corresponding fault planes, and rupture processes. Ce...

Four medium-sized earthquakes (Mw Global CMT project 5.5, 5.6, 5.9, 6.3; hereinafter named Topolobampo, Angel de la Guarda, San Lorenzo, and Loreto earthquakes, respectively) located in the Gulf of California Extensional Province were studied to obtain their kinematic rupture processes. A network of broadband seismic stations located around the Gul...

Nominally continuous data in space and/or time is obtained in various observations in geophysics. Due to an enhanced technology of computers, we can now invert such observed data with a very high sampling rate. Densely sampled observed data are usually not completely independent of each other, and so we must take this effect into account. As for se...

In geophysical observations, unlike the case of laboratory experiments, data are always inaccurate and insufficient, and so, we need to introduce some prior constraints in order to compromise reciprocal requirements for model resolution and estimation errors in a natural way. For seismic source inversion, smoothness constraints in space and time is...

As computer technology advanced, it has become possible to observe seismic wave with a higher sampling rate and perform inversion for a larger data set. In general, to obtain a finer image of seismic source processes, waveform data with a higher sampling rate are needed. Then we encounter a problem whether there is no limitation of sampling rate in...

A large earthquake (M7.2) occurred along the plate boundary offMiyagi Prefecture (Miyagi-Oki), northeastern Japan, on August 16, 2005. In this area, large earthquakes (~M7.5) have occurred repeatedly at intervals of about 37 years, and more than 27 years have passed since the last event occurred. To estimate the relationship between this earthquake...

1] We calculated static stress changes from the devastating M = 7.6 earthquake that shook Kashmir on 8 October, 2005. We mapped Coulomb stress change on target fault planes oriented by assuming a regional compressional stress regime with greatest principal stress directed orthogonally to the mainshock strike. We tested calculation sensitivity by va...

There now exist numerous cases in which InSAR data have been used to estimate the distribution of coseismic slip on faults during earthquakes. InSAR data are largely very well suited for this task, having both high spatial resolution and large areal coverage on the ground, which translate to good spatial resolution at depth. The disadvantage with u...

1] We investigate the validity of a method for estimating the critical slip-weakening distance (D c), which was proposed by Mikumo and Yagi [2003], for a dynamic rupture model of a recent earthquake. Assuming a uniform distribution of D c on the fault, we simulated spontaneous dynamic rupture process and generated the synthetic waveforms that would...

Plate boundary slip associated with the 2003 Off-Tokachi earthquake, northern Japan is determined by analysis of repeating earthquakes in the source region. A total of 251 repeating earthquake groups consisting of 666 events are identified in and around the aftershock region from October 1, 2000 to May 31, 2004. Although a number of the repeating e...