Kojiro Irikura

• Aichi Institute of Technology

On 18 June 2018, an Mw 5.5 inland crustal earthquake occurred in the northern Osaka Prefecture, Japan. This event is one of the most disastrous earthquakes bringing large ground motions with a maximum observed intensity of 6-lower on the Japan Meteorological Agency scale in and around the metropolitan Osaka area. Strong ground motions with larger p...

A set of source models was generated in previous studies by self-consistent fully dynamic rupture simulation in earthquake cycles. Source models were validated by comparison of simulated and observed ground motion, source scaling and maximum fault displacement values Dmax. In this study we compare fault displacements for three different types of fa...

Ground motions near the source area of the mainshock of the 2013 Lushan earthquake ( M w 6.6) in Sichuan Province in China were reproduced using the characterized source model and the empirical Green’s function method (EGFM). The best-fit characterized source model consisted of one strong motion generation area (SMGA) and a background area. The syn...

Japan Multi-hypocenter modelling of rupture propagation in the kinematic source modelling for strong-motion simulation becomes a widely accepted approach. In this approach, ruptures within SMGA's propagate from the sub-hypocenters assigned within each SMGA, while in background area rupture propagate from the main hypocenter of the earthquake. Direc...

Ground motions near the source area of the mainshock of the 2013 Lushan earthquake ( M w 6.6) in the Sichuan Province in China were reproduced using the characterized source model and the empirical Green’s function method (EGFM). The best-fit characterized source model consists of one strong motion generation area (SMGA) and a background area. The...

The main objective of this study is to develop physics-based constraints on the spatiotemporal variation of the slip-rate function using a simplified dynamic rupture model. First, we performed dynamic rupture modeling of the 2019 Mw 7.1 Ridgecrest, California, earthquake, to analyze the effects of depth-dependent stress and material friction on sli...

Physics-based dynamic rupture modelling is necessary for estimating parameters such as rupture velocity and slip rate function that are poorly resolved by seismic source inversion. In order to generate a large number of physically self-consistent rupture models, whose rupture process is consistent with the spatio-temporal heterogeneity of past eart...

Realistic dynamic rupture modeling validated by observed earthquakes is necessary for estimating parameters that are poorly resolved by seismic source inversion, such as stress drop, rupture velocity, and slip rate function. Source inversions using forward dynamic modeling are increasingly used to obtain earthquake rupture models. In this study, to...

Realistic dynamic rupture modelling validated by observed earthquakes is necessary for estimating parameters, such as stress drop, rupture velocity and slip rate function, that are poorly resolved by seismic source inversion. Source inversions using forward dynamic modelling are frequently used to obtain rupture models. Alternatively, in this study...

Dynamic rupture modelling is necessary for estimating parameters that are poorly resolved by seismic source inversion, such as rupture velocity and slip rate function. Source inversions using forward dynamic modelling are used to obtain rupture models, but their stress and strength heterogeneities are prescribed arbitrarily. In this study, to gener...

Extremely large ground motions with strong pulses were observed near source faults during two large MJMA 6.5 and MJMA 7.3 events of the 2016 Kumamoto earthquakes in Japan. To investigate the mechanisms for generation of near-source strong pulses during both events, we first performed strong ground motion simulations in a broadband frequency range b...

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 sca...

This paper describes a validated dynamic rupture model of the 2011 Tohoku earthquake that reproduces both long-period (20–100 s) and short-period (3–20 s) ground motions. In order to reproduce the observed large slip area (slip asperity), we assign a large Dc (slip critical distance) area following kinematic source inversion results. Sufficiently l...

We analyzed a kinematic earthquake rupture generator that combines the randomized spatial field approach of Graves and Pitarka (Bull Seismol Soc Am 106:2136–2153, 2016) (GP2016) with the multiple asperity characterization approach of Irikura and Miyake (Pure Appl Geophys 168:85–104, 2011) (IM2011, also known as Irikura recipe). The rupture generato...

Asperity models for ground motion prediction is widely used in Japan. Here we expand the application of these asperity models to predict fault displacement caused by surface rupture. The proposed approach is rather simple and practical for the use in fault displacement hazard analysis in nuclear installations and other critical infrastructures, as...

Strong ground motions from the 2016 Mw 7.0 Kumamoto earthquake (Japan) can be well simulated based on a characterized source model consisting of strong-motion generation areas (SMGAs) with high stress drop and a background area with low stress drop, except at very near-fault stations (Irikura et al. in Earth Planets Sp 69:10, 2017). Strong ground m...

The 2016 Kumamoto earthquake occurred on April 16, 2016, and induced the complex distribution of surface ruptures and fault displacements, which revealed the difficulty of evaluating off-fault displacement hazards. The evaluation of off-fault displacements is necessary for the site investigation of an important facility, such as nuclear installatio...

Vietnam has a low-to-moderate seismicity, but the currently available strong ground motion data used as a basis for a seismic-resistant design are insufficient. Generally, to overcome this issue, strong ground motions recorded at other places around the world are used, which have similar seismic, tectonic and physical earthquake characteristics, su...

In recent years the International Atomic Energy Agency (IAEA) has been closely following and supporting the use of physics-based rupture models for ground motion prediction (e.g. IAEA Safety Standards Series No. SSG–9 and Safety Report Series No. 85) as well as for fault displacement prediction (IAEA-TECDOC, in preparation), respectively for applic...

We examined high-frequency spectral decay characteristics of ground motions for inland crustal earthquakes in Japan, which are important in strong ground motion predictions. We examined 105 earthquakes (Mw 3.3–7.1), including seven large earthquakes (Mw 5.9–7.1). Spectral decay characteristics were accurately evaluated assuming the ω-squared source...

In this study, changes of response characteristics, including natural frequency, mode shape, and shear-wave propagation, of a 1/3 scaled specimen of an 18-story steel structure corresponding to different damage patterns, plasticizing, yielding, breaking, buckling of beam and columns members, are examined. Though the natural frequencies decrease wit...

Dynamic rupture modelling is necessary for estimation of parameters such as rupture velocity and slip rate function that are poorly resolved by seismic source inversion. Dynamic source inversions are used to obtain rupture models, but their stress and strength heterogeneities are prescribed arbitrarily. In this study, to generate a large number of...

Numerical modeling is a necessary tool for the assessment of variability strong ground motions in potential devastating large earthquakes. In a simulation-based seismic hazard analysis, it is critical to be able to generate a large number of physically self-consistent source models whose rupture process captures the main physics of earthquake ruptu...

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Empirical earthquake scaling relations play a central role in fundamental studies of earthquake physics and in current practice of earthquake hazard assessment, and are being refined by advances in earthquake source analysis. A scaling relation between seismic moment (M0) and rupture area (A) currently in use for ground motion prediction in Japan f...

Inspired by the first workshop on Best Practices in Physics-Based Fault Rupture Models for Seismic Hazard Assessment of Nuclear Installations (BestPSHANI) conducted by the International Atomic Energy Agency (IAEA) on 18–20 November, 2015 in Vienna (http://www-pub.iaea.org/iaeameetings/50896/BestPSHANI), this PAGEOPH topical volume collects several...

We analyzed the performance of the Irikura and Miyake (Pure and Applied Geophysics 168(2011):85–104, 2011) (IM2011) asperity-based kinematic rupture model generator, as implemented in the hybrid broadband ground motion simulation methodology of Graves and Pitarka (Bulletin of the Seismological Society of America 100(5A):2095–2123, 2010), for simula...

This volume collects several extended articles from the first workshop on Best Practices in Physics-based Fault Rupture Models for Seismic Hazard Assessment of Nuclear Installations (BestPSHANI). Held in 2015, the workshop was organized by the IAEA to disseminate the use of physics-based fault-rupture models for ground motion prediction in seismic...

A two-stage scaling relationship of the source parameters for crustal earthquakes in Japan has previously been constructed, in which source parameters obtained from the results of waveform inversion of strong motion data are combined with parameters estimated based on geological and geomorphological surveys. A three-stage scaling relationship was s...

In this study, we estimated source process of the 2016 Kumamoto earthquake from strong-motion data by using the multiple-time window linear kinematic waveform inversion method to discuss generation of strong motions and to explain crustal deformation pattern with a seismic source inversion model. A four-segment fault model was assumed based on the...

Under the diffuse field approximation, the full-wave (FW) microtremor H/V spectral ratio (H/V) is modeled as the square root of the ratio of the sum of imaginary parts of the Green’s function of the horizontal components to that of the vertical one. For a given layered medium, the FW H/V can be well approximated with only surface waves (SW) H/V of...

Spectral decay characteristics in high frequency range due to large and small inland crustal earthquakes that occurred in Japan are examined. The Butterworth type high-cut filter with cut-off frequency, fmax and its power coefficient of high-frequency decay is assumed in this study. Four parameters such as seismic moment Mo, corner frequency fc, fm...

Inspired by the first workshop on Best Practices in Physics-Based Fault Rupture Models for Seismic Hazard Assessment of Nuclear Installations (BestPSHANI) conducted by the International Atomic Energy Agency (IAEA) on 18–20 November, 2015 in Vienna (http://www-pub.iaea.org/iaeameetings/50896/BestPSHANI), this PAGEOPH topical volume collects several...

Though the 2014 Ludian Earthquake had only a moderate magnitude (Ms 6.5), high-level ground motions of almost 1g occurred at Longtoushan Town (seismic station 53LLT), which located near the intersection of a conjugate-shaped seismogenic fault. The building damages on the pluvial fan and the river terrace at Longtoushan was clearly different. In ord...

Seismic and tsunami waves were the most destructive phenomena during the 2011 Tohoku earthquake. Here we ask whether the same source model can be used to obtain equally good simulations of the observed strong ground motions and the tsunami waves. If so, we could use the same source modeling technique for predictions of both tsunami waves and strong...

This study is aiming to construct source model for simulating long-period motions (2-10 seconds) that cause damage of long-period structures (e.g. Skyscrapers, and large petroleum storage tanks) for mega-thrust subduction earthquakes. The large slip area caused catastrophic tsunamis was located on the shallow area near the Japan trench during the 2...

We analyzed the performance of the Irikura and Miyake (Pure and Applied Geophysics 168(2011):85–104, 2011) (IM2011) asperity-based kinematic rupture model generator, as implemented in the hybrid broadband ground motion simulation methodology of Graves and Pitarka (Bulletin of the Seismological Society of America 100(5A):2095–2123, 2010), for simula...

Open Acess link: http://rdcu.be/oOL9 Empirical earthquake scaling relations play a central role in fundamental studies of earthquake physics and in current practice of earthquake hazard assessment, and are being refined by advances in earthquake source analysis. A scaling relation between seismic moment (M0) and rupture area (A) currently in use f...

In this study, empirical fragility curves expressed in terms of relationship between damage ratio indices of buildings and ground motion indices were developed in northern Miyagi prefecture located in nearfield areas during the 2011 off the Pacific coast of Tohoku Earthquake. The ground motion indices were evaluated from observed ground motions at...

In this article, ground-motion prediction equations (GMPEs) based on the horizontal components of the strong-motion records from shallow crustal and upper-mantle earthquakes in Japan are presented. We assembled a large dataset from earthquakes with a moment magnitude (M-w) over 4.9 and a reliable earthquake category (the tectonic location of earthq...

The frequency content of strong ground motions from subduction slab earthquakes differs significantly from that of ground motions produced by other categories (tectonic locations: shallow crustal, upper mantle, and subduction interface) of earthquakes in subduction zones. In the last two decades, a large number of records from subduction slab event...

We presented a set of ground-motion prediction equations (GMPEs) for the horizontal components of strong-motion records from subduction interface events in Japan. We assembled and processed in a consistent manner a large set of strong-motion records from reliably identified subduction interface events up to the end of 2012. The GMPEs were based on...

Using the waveform inversion results of recent eighteen crustal earthquakes (Mw5.4-6.9) in Japan, which happened after the 1995 Hyogo-ken Nanbu earthquake, we extracted the source parameters (entire rupture area (S) and asperity area (Sa)) from the inverted heterogeneous slip distributions following the criterion of Somerville et al.(1999). We reco...

Because shaking modes of super high-rise buildings are very complicated, it is not enough to perform health-monitoring only for the whole structures. We try to extract story-by-story shear-wave velocities applying the deconvolution method to microtremor records measured at super high-rise buildings. The shear-wave propagation (including reflection,...

This study compares the nonlinear response potential of generic inelastic single-degree-of-freedom systems subjected to three sets of ground motion records for the 2011 Tohoku mainshock. The compared record sets, all for the same sites, are: (i) observed accelerograms at 48 KiK-net strong motion stations; (ii) time-histories simulated from the empi...

We construct a new method for reasonable evaluation of seismic bedrock spectra using borehole records observed at KiK-net sites. In detail, the method first reduces the observed spectra at borehole stations to seismic bedrock spectra, and then derives corner frequency and Q-value characterizing the source and path effects from the reduced spectra....

We examined a new scaling relation between source area S and seismic moment M 0 for large crustal earthquakes on “mega-fault” systems, including earthquakes with magnitudes larger than M w7.4. We focused on earthquakes that occurred on inland crustal mega-fault systems, such as the 2008 Wenchuan and 2002 Denali earthquakes, and compiled the source...

We investigated broadband evidence of the rupture directivity effect and estimated stress drop for the 2013 Nantou blind-thrust earthquakes (the 0327 and 0602 crustal events) from three individual analyses using empirical Green’s functions: deconvolution source time function analysis, source spectral ratio analysis, and broadband waveform modeling...

We have constructed a short-period source model for the 2011 M-w 9.0 Off the Pacific Coast of Tohoku earthquake using strong-motion records at stations near the source fault. The observed strong motions contain five wavepackets that correspond to specific strong-motion generation areas (SMGAs). The origins of the wavepackets were retrieved from the...

Records of the Niigata Chuetsu-Oki earthquake (July, 16, 2007, M w = 6.6, depth ~17 km) and its aftershocks from seismic vertical arrays deployed at the territory of the Kashiwazaki-Kariwa nuclear power plant (~15 km from the fault) are used to study the soil behavior down to ~250 m during strong ground motion. Nonlinear models of soil behavior dur...

The question we addressing here is the possibility of evenly good simulation of observed ground motions and tsunami using the same source model. By comparing simulated and observed tsunami waves we test source inversion and characterization technique for M9 class event on example of the 2011 Tohoku earthquake. Simulation results fit observed tsunam...

2011 off the Pacific coast of Tohoku earthquake is one of the best geophysically-recorded great earthquakes and due to this numerous source models were generated using teleseismic, GPS, strong ground motion and tsunami data. The question we addressing here is the possibility of evenly good simulation of observed ground motions and tsunami using the...

Strong ground motions in the frequency range of 0.2-1 Hz observed along the east coast of Tohoku, Japan, from Miyagi to Ibaraki during the 2011 Tohoku earthquake are characterized by distinct pulses. The generation of such pulses is significantly important especially in the context of seismic design of structures. In this article, examples of stron...

Fragility curves, the relationships between three kinds of building damage ratios, i.e., total collapse ratio (TCR), collapse ratio (CR) and damage ratio (DR), as well as ground motion characteristics, i.e., peak ground acceleration (PGA), peak ground velocity (PGV), Japan Meteorological Agency instrumental seismic intensity (IJMA) and spectral int...

We have investigated the rupture process of the 2011 off the Pacific coast of Tohoku earthquake by the multi-time-window linear waveform inversion method using the long-period strong-ground motion data. From the record section of the long-period motion of the 3 phases, it is indicated that the rupture process mainly consists of the 3 stages. We ass...

A source model for generating strong ground motions during the 2011 off the Pacific coast of Tohoku Earthquake (M w 9.0) is estimated from a comparison of the observed records of the mainshock and synthetic motions, based on the characterized source model using the empirical Green’s function method. The characterized source model consists of severa...

Introduction The Earthquake Early Warning (EEW) system by Japan Metrological Agency in Japan provides the coordinate of the starting point, the origin time and the magnitude of target earthquakes based on a point source assumption. The seismic intensity at each site is calculated by using an attenuation distance relation and site amplification from...

Relationships between collapse ratios (CRs) of buildings and characteristics of strong ground motions during the 2008 Wenchuan earthquake was founded. Vulnerability functions of buildings were established in relation to PGA, PGV, PSA, and PPSv. Damage criteria for CR<10% corresponding to “minor and moderate damage” were PGA<250 gal, PGV<25 cm/s, PS...

We have investigated the rupture process of the 2011 off the Pacific coast of Tohoku Earthquake using a multi-time-window linear waveform inversion method using long-period strong-ground motion data. From the record section of the long-period motion of the 3 phases, it is indicated that the rupture process mainly consists of the 3 stages. We have a...

For mitigating seismic damage of structures during disastrous earthquakes, we have to improve both the procedure for constructing source models for future earthquakes and the method for estimating strong ground motions. The empirical Green's function method (EGFM) is one of the most appropriate methods for estimating strong ground motions near sour...

A set of large inland earthquake (Mw>7) rupture scenarios is generated using two-step dynamic rupture modeling approach. In the first step, a set of different-size earthquakes with dynamic input parameters is produced by quasi-dynamic multi-cycle simulation (Hillers et al., 2006; Hillers et al., 2007) governed by rate-and state-dependent friction l...

We developed a recipe for predicting strong ground motions based on a characterization of the source model for future crustal earthquakes. From recent developments of waveform inversion of strong motion data used to estimate the rupture process, we have inferred that strong ground motion is primarily related to the slip heterogeneity inside the sou...

Spectral decay characteristics in high frequency range due to mainshock and aftershocks of the 2005 Fukuoka-ken Seiho-oki Earthquake are examined. The Butterworth type high-cut filter with cut-off frequency, fmax and its power coefficient of high-frequency decay is assumed in this study. The four parameters such as seismic moment, corner frequency,...

We present a velocity model inversion approach using artificial neural networks (NN). We selected four aftershocks from the 2000 Tottori, Japan, earthquake located around station SMNH01 in order to determine a 1D nearby underground velocity model. An NN was trained independently for each earthquake-station profile. We generated many velocity models...

Since 2005, The Headquarters for Earthquake Research Promotion (HERP) has been publishing 'National Seismic Hazard Maps for Japan' to provide useful information for disaster prevention countermeasures for the country and local public agencies, as well as promote public awareness of disaster prevention of earthquakes. In the course of making the yea...

Spectral decay characteristics in high frequency range of observed records from crustal large earthquakes occurred in Japan is examined. It is very important to make clear spectral decay characteristics in high frequency range for strong ground motion prediction. Target earthquakes are three events, the 2003 Miyagi-Ken Hokubu earthquake (Mw : 6.1),...

Spectral decay characteristics in high frequency range due to mainshock and aftershocks of the 2005 Fukuoka-ken Seiho Oki Earthquake are examined. The Butterworth type high-cut filter with cut-off frequency fmax and its power coefficient is assumed in this study. The two parameters are estimated by fitting Fourier spectra of observed records at roc...

Extremely valuable strong-motion records during the 2008 Wenchuan earthquake were obtained at a number of stations close to the source region. We estimate the characterized source model for simulating ground motions using the empirical Green's function (EGF) method and the hybrid method using strong-motion data from the earthquake. The characterize...

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...

We proposed a procedure to establish a model of dynamic fault rupturing for predicting strong ground motions under the constraints by empirical relations among fault parameters of the surface and subsurface faults such as the fault length, the dislocation on the surface, the ruptured area, the seismic moment, and the short-period level of the accel...

In order to simulate ground motion during an earthquake, it is indispensable to properly estimate not only source and propagation path effects but also site effects caused by subsurface structures near the site. The site effects empirically estimated using seismic records are most reliable because velocity profiling of the structures is too difficu...

We investigate a special type of variability in response spectral amplification ratios computed from numerical “engineering” models for a soft soil site. The engineering models are defined by shallow soil layers over “engineering” bedrock with a shear-wave velocity over 600–700m/s and the model is subjected to vertical propagating shear waves. The...

We attempt to make the best-fit source models for simulating strong ground motions from the 2007 Niigata-ken Chuetsu-oki earthquake (Mw 6.6). We collected the source models obtained by the waveform inversion analysis and by the forward modeling using the strong motion data from the 2007 Chuetsu-oki earthquake. Observed records near source have thre...

On July 16, 2007, Off Mid-Niigata earthquake (Mw6.6) stroke the Kashiwazaki-Karima nuclear power plant. Amplitudes of ground motions at the KK1 site for example, exceeded designed amplitudes 2.5 times. Three large pulses are observed clearly on the velocity and displacement seismic records. They are interpreted as the asperity pulses. Different sou...

Very strong ground motions (maximum acceleration 993cm/s2 in the borehole seismometer point of -255m in depth) were observed in the Kashiwazaki Kariwa Nuclear Power Plant during the Niigataken Chuetsu-oki Earthquake on July 16, 2007. In this study, we tried to develop new method, which can simulate waveforms on free rock surface by using the bore h...

We propose a new technique for evaluating empirical site effects in time domain, extending the concept of Birgören and Irikura (2005). They developed a method for estimating coherent site effects by averaging wavelet coefficients of the Meyer-Yamada wavelet for many seismic records. In general, site effects consist of coherent and incoherent signal...

Originated by Alterman and Karal (AK) in 1968 as a domain-coupling technical algorithm, the generalized hybrid approach of wave injection is described by binding two subvolumes treated per partes by arbitrary wave-propagation methods. The generalized AK two-step procedure combines the source and path effects computed by one arbitrary method and loc...

Studies that estimate low-frequency Q-value are very scarce. In most of them estimations are made by eye or by trial and error, without any systematic inversion approach. In this study, we propose nonlinear waveform inversion methodology and estimate low-frequency Q-value from the observation data. Results will help us to improve accuracy of the nu...

Average envelopes of small earthquakes represent a convenient basis for the construction of semi-empirical stochastic Green's functions, used for prediction of future strong ground motions. Petukhin and Gusev (2003) proposed method for estimation of the average envelopes at rock sites based on assumption of self-similarity of envelopes and applied...

This paper describes the generalized hybrid approach of wave injection for elastic linear case originated by Alterman and Karal (AK) in 1968 as a domain coupling technical algorithm. The general approach is described by binding two sub-volumes treated per partes by arbitrary wave-propagation methods. The generalized AK two-step procedure possibly c...

In the context of the slip-weakening friction model and simplified asper-ity models for stress state, we calibrate dynamic rupture models for buried and surface-rupturing earthquakes constrained with statistical observations of past earth-quakes. These observations are the kinematic source models derived from source in-versions of ground-motion and...

A source model for estimating broad-band ground motions from the 2007 Noto-Hanto earthquake (M w 6.7) is estimated from a comparison of the observed records of the mainshock and synthesized motions based on the characterized asperity model using the empirical Green’s function method. The observed records of aftershocks used as the empirical Green’s...

A waveform inversion with empirical Green's functions was conducted to estimate strong-motion generation areas (SMGAs) of the 2003 Tokachi-oki, Japan, earthquake (Mw 8.3). Although the rupture process of this great subduction-zone earthquake has been revealed with waveform inversions based on low-frequency (lower than 0.2 Hz) ground motions, it is...

Ground motions from inland-crust earthquakes are simulated using a characterized source model with asperities in an entire rupture area. The characterized model is constructed based on the "recipe" we proposed. Validity and applicability of the "recipe" has been examined by comparing observed ground motions with synthesized ones for recent disastro...

High-cut frequency characteristics of ground motions for inland crustal earthquakes occurring in Japan are examined. It is very important to make clear spectral decay characteristics in high frequency range for strong ground motion prediction. The target earthquakes are the 2003 Miyagi-ken Hokubu earthquake (Mw:6.1) and the 2005 Fukuoka-ken Seiho-o...