Broadband Ground Motion Simulation Research Articles

Broadband Ground Motion Simulation of the 2004 and 1977 Vrancea, Romania, Earthquakes Using Empirical Green’s Function Method

We estimated the parameters of strong motion generation areas and simulated broadband ground motions for the moderate October 27, 2004 (M w 5.8) and damaging March 4, 1977 (M w 7.4) Vrancea (Romania) intermediate-depth subduction earthquakes using the empirical Green’s function method. The method allows the simulation of ground motions in a broadband frequency range by summing up the subevent records, corresponding to small magnitude events in the near-source areas, which are assumed to follow the source-scaling relationship and the omega-square source spectral model. We first estimated the strong motion generation area that reproduces near-source ground motions in a broadband frequency range of 0.3–10 Hz for the 2004 earthquake, by fitting the synthetic acceleration, velocity, and displacement waveforms to the observed data. The source properties of the obtained strong motion generation area are in agreement with the predictions made using an empirical source scaling relationship for crustal earthquakes, implying a stress drop of approximately 10 MPa for the 2004 earthquake. We then modeled the strong motion generation area for the 1977 damaging earthquake using the 2004 earthquake as an empirical Green’s function and constructing a source model based on its estimated source parameters. To simulate the unique record at Bucharest, capital city of Romania, the rupture was assumed to have propagated from the northeast bottom of the strong motion generation area having a stress drop of 50 MPa. Broadband ground motion simulations were further compared in terms of the modified Mercalli intensity values, calculated from the peak ground accelerations and peak ground velocities of synthetic waveforms, with the observed Medvedev–Sponheuer–Karnik intensity values. Our estimates of the source properties for the 2004 and 1977 Vrancea intermediate-depth earthquakes support the size-dependent stress drop.

Near-Fault Broadband Ground Motion Simulations Using Empirical Green’s Functions: Application to the Upper Rhine Graben (France–Germany) Case Study

Seismic hazard estimation relies classically on databased ground motion prediction equations (GMPEs) giving the expected motion level as a function of several parameters characterizing the source and the sites of interest. However, records of moderate to large earthquakes at short distances from the faults are still rare. For this reason, it is difficult to obtain a reliable ground motion prediction for such a class of events and distances where also the largest amount of damage is usually observed. A possible strategy to fill this lack of information is to generate synthetic accelerograms based on an accurate modeling of both extended fault rupture and wave propagation process. The development of such modeling strategies is essential for estimating seismic hazard close to faults in moderate seismic activity zones, where data are even scarcer. For that reason, we selected a target site in Upper Rhine Graben (URG), at the French–German border. URG is a region where faults producing micro-seismic activity are very close to the sites of interest (e.g., critical infrastructures like supply lines, nuclear power plants, etc.) needing a careful investigation of seismic hazard. In this work, we demonstrate the feasibility of performing near-fault broadband ground motion numerical simulations in a moderate seismic activity region such as URG and discuss some of the challenges related to such an application. The modeling strategy is to couple the multi-empirical Green’s function technique (multi-EGFt) with a k −2 kinematic source model. One of the advantages of the multi-EGFt is that it does not require a detailed knowledge of the propagation medium since the records of small events are used as the medium transfer function, if, at the target site, records of small earthquakes located on the target fault are available. The selection of suitable events to be used as multi- EGF is detailed and discussed in our specific situation where less number of events are available. We then showed the impact that each source parameter characterizing the k−2 model has on ground motion amplitude. Finally we performed ground motion simulations showing results for different probable earthquake scenarios in the URG. Dependency of ground motions and of their variability are analyzed at different frequencies in respect of rupture velocity, roughness degree of slip distribution (stress drop), and hypocenter location. In near-source conditions, ground motion variability is shown to be mostly governed by the uncertainty on source parameters. In our specific configuration (magnitude, distance), the directivity effect is only observed in a limited frequency range. Rather, broadband ground motions are shown to be sensitive to both average rupture velocity and its possible variability, and to slip roughness. Ending up with a comparison of simulation results and GMPEs, we conclude that source parameters and their variability should be set up carefully to obtain reliable broadband ground motion estimations. In particular, our study shows that slip roughness should be set up in respect of the target stress drop. This entails the need for a better understanding of the physics of earthquake source and its incorporation in the ground motion modeling.

Accounting for Fault Roughness in Pseudo-Dynamic Ground-Motion Simulations

Geological faults comprise large-scale segmentation and small-scale roughness. These multi-scale geometrical complexities determine the dynamics of the earthquake rupture process, and therefore affect the radiated seismic wavefield. In this study, we examine how different parameterizations of fault roughness lead to variability in the rupture evolution and the resulting near-fault ground motions. Rupture incoherence naturally induced by fault roughness generates high-frequency radiation that follows an ω-2 decay in displacement amplitude spectra. Because dynamic rupture simulations are computationally expensive, we test several kinematic source approximations designed to emulate the observed dynamic behavior. When simplifying the rough-fault geometry, we find that perturbations in local moment tensor orientation are important, while perturbations in local source location are not. Thus, a planar fault can be assumed if the local strike, dip, and rake are maintained. We observe that dynamic rake angle variations are anti-correlated with the local dip angles. Testing two parameterizations of dynamically consistent Yoffe-type source-time function, we show that the seismic wavefield of the approximated kinematic ruptures well reproduces the radiated seismic waves of the complete dynamic source process. This finding opens a new avenue for an improved pseudo-dynamic source characterization that captures the effects of fault roughness on earthquake rupture evolution. By including also the correlations between kinematic source parameters, we outline a new pseudo-dynamic rupture modeling approach for broadband ground-motion simulation.

Physically based probabilistic seismic hazard analysis using broadband ground motion simulation: a case study for the Prince Islands Fault, Marmara Sea

The main motivation for this study was the impending occurrence of a catastrophic earthquake along the Prince Island Fault (PIF) in the Marmara Sea and the disaster risk around the Marmara region, especially in Istanbul. This study provides the results of a physically based probabilistic seismic hazard analysis (PSHA) methodology, using broadband strong ground motion simulations, for sites within the Marmara region, Turkey, that may be vulnerable to possible large earthquakes throughout the PIF segments in the Marmara Sea. The methodology is called physically based because it depends on the physical processes of earthquake rupture and wave propagation to simulate earthquake ground motion time histories. We included the effects of all considerable-magnitude earthquakes. To generate the high-frequency (0.5–20 Hz) part of the broadband earthquake simulation, real, small-magnitude earthquakes recorded by a local seismic array were used as empirical Green’s functions. For the frequencies below 0.5 Hz, the simulations were obtained by using synthetic Green’s functions, which are synthetic seismograms calculated by an explicit 2D/3D elastic finite difference wave propagation routine. By using a range of rupture scenarios for all considerable-magnitude earthquakes throughout the PIF segments, we produced a hazard calculation for frequencies of 0.1–20 Hz. The physically based PSHA used here followed the same procedure as conventional PSHA, except that conventional PSHA utilizes point sources or a series of point sources to represent earthquakes, and this approach utilizes the full rupture of earthquakes along faults. Furthermore, conventional PSHA predicts ground motion parameters by using empirical attenuation relationships, whereas this approach calculates synthetic seismograms for all magnitudes of earthquakes to obtain ground motion parameters. PSHA results were produced for 2, 10, and 50 % hazards for all sites studied in the Marmara region.

Broadband Strong Ground Motion Simulations of Large Subduction Earthquakes

The great subduction earthquakes that occurred recently in Peru, Chile, and Japan have provided unprecedented information about the ground motions generated by such earthquakes. The 23 June 2001 M 8.4 Peru earthquake was recorded at eight strong-motion stations; the 27 February 2010 M 8.8 Maule, Chile, earthquake was recorded at over 10 strong-motion stations; and the 11 March 2011 M 9.0 Tohoku, Japan, earthquake was recorded at more than a thousand stations and produced the most extensive dataset of recordings for any earthquake. For the first time, data are available to guide the generation of ground-motion simulations from great subduction earthquakes. Broadband ground-motion simulations can enhance the usefulness of the recordings of these earthquakes by providing a means of interpolating and extrapolating the recorded data. Once they have been validated, broadband ground-motion simulations can be used for forward predictions of the ground motions of great subduction events in regions such as Cascadia, in which there are no strong-motion recordings of large subduction earthquakes. In this study, we test our ability to use a hybrid method to simulate broadband strong-motion recordings of megathrust earthquakes by demonstrating that our simulations reproduce the amplitudes of the recorded ground motions without systematic bias. We use simulations to study the distribution of various intensity measures of ground motion caused by these earthquakes and to validate our ground-motion simulation method by comparing the simulated ground motions with recorded ground motions as well as with empirical ground-motion prediction models.

Evaluation of Hybrid Broadband Ground Motion Simulations for Response History Analysis and Design

Chapter 16 of ASCE 7 governs the selection of ground motions for analysis of new buildings and requires recordings that meet specified criteria. If a sufficient number of recordings cannot be found, it allows the use of “appropriate simulated ground motions,” but does not provide further guidance. This paper outlines a procedure for generating and selecting a set of “appropriate” hybrid broadband simulations and a comparable set of recordings. Both ground motion sets are used to analyze a building in Berkeley, California, and the predicted structural performance is compared. The structural behavior resulting from recordings and simulations is similar, and most discrepancies are explained by differences in directional properties such as orientation of the maximum spectral response. These results suggest that when simulations meet the criteria outlined for recordings in ASCE 7 and properties such as directionality are realistically represented, simulations provide useful results for structural analysis and design.

Values for peak ground acceleration and peak ground velocity using in seismic hazard assessment for Song Tranh 2 hydropower region

Values for peak ground acceleration and peak ground velocity using in seismic hazard assessment for Song Tranh 2 hydropower region

PSHA for Broad-Band Strong Ground-Motion Hazards in the Saronikos Gulf, Greece, from Potential Earthquake with Synthetic Ground Motions

We perform a probabilistic seismic hazard analysis (PSHA) for broad-band strong ground motion within the Saronikos Gulf region, Greece, from potential earthquakes along the 30 km long Aigina fault in the northern part of the Gulf. We perform the PSHA utilizing empirical Green’s functions (EGFs) merged with synthetic Green’s functions (SGFs) along with models of finite rupture in place of standard “attenuation relations.” Our approach considers all significant magnitudes for PSHA and full broadband ground motion simulations. Calculations are source and site specific, and could reduce uncertainties in estimating standard engineering parameters. We use a range of rupture scenarios for all significant magnitude earthquakes along the fault. The hazard calculation is for frequencies 0.0– 15.0 Hz. Recordings of small earthquakes from an onshore/offshore local seismic array were used as EGFs for frequencies of 1.5–15.0 Hz, the finite difference code E3D was utilized to synthesize SGFs for frequencies 0.0–1.5 Hz, and an algorithm for merging the EGFs with SGFs was developed. The full-waveform calculations are important for non-linear dynamic analysis of structures in the coastal zone and potential hazard to long period structures. Results of proposed PSHA identify 2%, 10%, and 50% hazard at the selected sites of Saronikos Gulf.Finally, we compare our PSHA results to those obtained by standard practice which involves prediction equations (GMPEs) recently developed in the Next Generation Attenuation (NGA) project and empirical predictive attenuation relations proposed for Greece. We believe that differences with the NGA results are due to site- and source-specific information utilized in this study, and incorporation of this information may significantly reduce the uncertainty in seismic hazard calculations.

Bias assessment in Incremental Dynamic Analysis due to record scaling

Incremental Dynamic Analysis (IDA) involves a series of nonlinear response history analyses with a suite of incrementally scaled ground motion records. Although IDA is perhaps the most comprehensive seismic performance assessment method, it receives criticism because several ground motion records are scaled up until the structure collapses. The scaling practice often results to unrealistic multipliers, thus modifying the amplitude of the ground motion and introducing bias on the structural performance estimation. Record scaling is a common practice in earthquake engineering due to the lack of natural records corresponding to large magnitudes and/or small distances from the fault rupture location. In this work we use a large number of ground motion records to compare the predictions of IDA with that of unscaled ground motions and we propose a new methodology in order to quantify the bias introduced in IDA. Apart from natural records, we have conducted broadband ground motion simulations for rupture scenarios of weak, medium and large magnitude events in order to expand our record database. The investigation is performed on a series of inelastic single-degree-of-freedom systems and on two multistory steel moment frame buildings. The results pinpoint both qualitatively and quantitatively, for the full range of limit-states, the bias that IDA introduces on the structural performance estimation.

Calibration of a Semi-Stochastic Procedure for Simulating High-Frequency Ground Motions

Broadband ground motion simulation procedures typically utilize physics-based modeling at low frequencies, coupled with semi-stochastic procedures at high frequencies. The high-frequency procedure considered here combines deterministic Fourier amplitude spectra (dependent on source, path, and site models) with random phase. Previous work showed that high-frequency intensity measures from this simulation methodology attenuate faster with distance and have lower intra-event dispersion than in empirical equations. We address these issues by increasing crustal damping (Q) to reduce distance attenuation bias and by introducing random site-to-site variations to Fourier amplitudes using a lognormal standard deviation ranging from 0.45 for Mw< 7 to zero for Mw8. Ground motions simulated with the updated parameterization exhibit significantly reduced distance attenuation bias and revised dispersion terms are more compatible with those from empirical models but remain lower at large distances (e.g., > 100 km).

Fault Process and Broadband Ground-Motion Simulations of the 23 October 2011 Van (Eastern Turkey) Earthquake

Abstract On 23 October 2011 an M w 7.1 earthquake occurred in eastern Turkey, close to the towns of Van and Ercis, causing more than 600 casualties and widespread structural damage. The earthquake ruptured a 60–70 km long northeast–southwest fault with a thrust mechanism, in agreement with regional tectonic stress regime. We studied the fault process of the event and the recorded ground motions using different sets of data. Regional records (0.005–0.010 Hz) are used to constrain the centroid moment tensor solution. Near‐regional data, 100–200 km from the fault, are used for relocation of the hypocenter and, in the frequency range 0.05–0.15 Hz, for inversion of the rupture propagation by two methods: multiple point‐source model (ISOLA) and multiple finite‐extent (MuFEx) source model. MuFEx also provides an estimate of the model uncertainty, which is quite large due to unfavorable station distribution. We arrive at several plausible scenarios (equally well fitting the observed data including Global Positioning System coseismic displacements) with different styles of the rupture propagation. A few alternative source models are used for broadband (0.1–10 Hz) ground‐motion simulations by means of the hybrid integral‐composite source model. Only models comprising source complexities, such as a delayed rupture of shallow asperities, enable explanation of the acceleration record at the only available near‐fault station, which exhibits a long duration and two prominent wave groups. These complex rupture models are used to simulate the ground motion in the near‐fault area, specifically, at Van and Ercis, where records of the mainshock were missing, providing reasonable agreement with the observed spatial distribution of damage.

Broadband Ground-Motion Simulation of an Intraslab Earthquake and Nonlinear Site Response: 2010 Ferndale, California, Earthquake Case Study

Intraslab earthquakes are generated by fault ruptures, which occur at shallow (20–60 km) or deep (>60 km) parts of a subducting tectonic plate slab. In both cases the rupture occurs in the vicinity of a zone with large velocity contrast and increased regional stress caused by the subducting plates. These conditions have significant effects on fault geometry, rupture dynamics, and seismic energy, which in turn affect the amplitude and duration of ground motion. Consequently, intraslab earthquakes can generate larger ground motion than shallow crustal earthquakes of same magnitude. Therefore their study is very important for strong ground motion prediction and seismic‐hazard assessment. In an effort to develop a methodology for simulating strong ground motion from intraslab earthquakes we tested the broadband ground‐motion simulation technique of Graves and Pitarka (2010) in modeling ground motion recorded from the M 6.5 2010 Ferndale, California, intraslab earthquake. The Graves and Pitarka (2010) method was originally developed for simulating crustal earthquakes. To our knowledge this is the first attempt to apply a broadband ground‐motion‐simulation method in modeling ground motion from intraslab earthquakes in the United States. A similar approach (Matsuzaki et al. , 2010) was applied to studying the rupture process of the 2001 Geiyo, Japan, intraslab earthquake using the recipe developed by Irikura and Miyake (2006). In this study we simulate and analyze ground‐motion‐acceleration time history recorded during the earthquake in a zone between Ferndale and Eureka, and Humboldt Bay. The earthquake was very well recorded in a geotechnical array located in the Humboldt Bay soft sediments. The ground‐motion acceleration recorded by the array’s instruments at several depths provided a good opportunity for testing numerical techniques and empirical models of the nonlinear seismic response of soils for input motion with moderate amplitude. A large part of our investigation is focused on modeling the observed nonlinear response …

Validation of Ground-Motion Simulations for Historical Events Using SDoF Systems

The study presented in this paper is among the first in a series of studies toward the engineering validation of the hybrid broadband ground-motion simulation methodology by Graves and Pitarka (2010). This paper provides a statis- tical comparison between seismic demands of single degree of freedom (SDoF) systems subjected to past events using simulations and actual recordings. A number of SDoF systems are selected considering the following: (1) 16 oscillation periods between 0.1 and 6 s; (2) elastic case and four nonlinearity levels, from mildly inelastic to severely inelastic systems; and (3) two hysteretic behaviors, in particular, nondegrading-nonevolutionary and degrading-evolutionary. Demand spectra are de- rived in terms of peak and cyclic response, as well as their statistics for four historical earthquakes: 1979 Mw 6.5 Imperial Valley, 1989 Mw 6.8 Loma Prieta, 1992 Mw 7.2 Landers, and 1994 Mw 6.7 Northridge. The results of this study show that both elastic and inelastic demands from simu- lated and recorded motions are generally similar. However, for some structural sys- tems, the inelastic response to simulated accelerograms may produce median demands that appear different from those obtained using corresponding recorded motions. The magnitude of such differences depends on the SDoF period, the nonlinearity level, and, to a lesser extent, the hysteretic model used. In the case of peak response, these dis- crepancies are likely due to differences in the spectral shape, while the differences in terms of cyclic response can be explained by some integral parameters of ground motion (i.e., duration-related). Moreover, the intraevent standard deviation values of structural demands calculated from the simulations are generally lower than those given by recorded ground motions, especially at short periods. The assessment of the results using formal statistical hypothesis tests indicates that, in most cases, the dif- ferences found are not significant, increasing the trust in the use of simulated motions for engineering applications.

Sensitivity of broad-band ground-motion simulations to earthquake source and Earth structure variations: an application to the Messina Straits (Italy)

In this paper, we investigate ground-motion variability due to different faulting approximations and crustal-model parametrizations in the Messina Straits area (Southern Italy). Considering three 1-D velocity models proposed for this region and a total of 72 different source realizations, we compute broad-band (0-10 Hz) synthetics for Mw 7.0 events using a fault plane geometry recently proposed. We explore source complexity in terms of classic kinematic (constant rise-time and rupture speed) and pseudo-dynamic models (variable rise-time and rupture speed). Heterogeneous slip distributions are generated using a Von Karman autocorrelation function. Rise-time variability is related to slip, whereas rupture speed variations are connected to static stress drop. Boxcar, triangle and modified Yoffe are the adopted source time functions. We find that ground-motion variability associated to differences in crustal models is constant and becomes important at intermediate and long periods. On the other hand, source-induced ground-motion variability is negligible at long periods and strong at intermediate-short periods. Using our source-modelling approach and the three different 1-D structural models, we investigate shaking levels for the 1908 Mw 7.1 Messina earthquake adopting a recently proposed model for fault geometry and final slip. Our simulations suggest that peak levels in Messina and Reggio Calabria must have reached 0.6-0.7 g during this earthquake.

Site- and ground motion-dependent nonlinear effects in seismological model predictions

We investigate the empirical relationship between site response nonlinearity, soil properties, and ground motion characteristics, as a first step to enable efficient integration of nonlinear analyses in broadband ground motion simulations. For this purpose, we use 24 downhole array sites with detailed geotechnical information and subject the profiles to broadband ground motion synthetics. We quantify the extent of soil nonlinearity in site-specific response analyses by estimating the divergence between linear and nonlinear ground surface predictions. We show that the parameters controlling the nonlinear response are V S 30 (weighted averaged shear wave velocity in the top 30 m of the soil profile), the site amplification at the fundamental frequency (Amp), the peak ground acceleration (PGA), and the frequency index (FI), a quantitative measure we define to characterize how well the incident motion can “see” the near-surface soil layers. Using the synthetic results, we quantitatively describe the error introduced in ground motion predictions when nonlinear effects are not accounted for, and show that the error is both site and ground motion dependent. Our study indicates that to characterize the susceptibility of a soil profile to nonlinear effects, V S 30 should be complemented with measures of the soil–rock impedance contrast, as well as measures of the ground motion intensity and frequency content.

Erratum to Hybrid Broadband Ground-Motion Simulations: Combining Long-Period Deterministic Synthetics with High-Frequency Multiple S-to-S Backscattering

Erratum to Hybrid Broadband Ground-Motion Simulations: Combining Long-Period Deterministic Synthetics with High-Frequency Multiple S-to-S Backscattering

Broadband Ground-Motion Simulation Using a Hybrid Approach

This paper describes refinements to the hybrid broadband ground-motion simulation methodology of Graves and Pitarka (2004), which combines a deterministic approach at low frequencies ( f 1 Hz). In our approach, fault rupture is represented kinematically and incorporates spatial heterogeneity in slip, rupture speed, and rise time. The prescribed slip distribution is constrained to follow an inverse wavenumber-squared fall-off and the average rupture speed is set at 80% of the local shear-wave velocity, which is then adjusted such that the rupture propagates faster in regions of high slip and slower in regions of low slip. We use a Kostrov-like slip-rate function having a rise time proportional to the square root of slip, with the average rise time across the entire fault constrained empirically. Recent observations from large surface rupturing earthquakes indicate a reduction of rupture propagation speed and lengthening of rise time in the near surface, which we model by applying a 70% reduction of the rupture speed and increasing the rise time by a factor of 2 in a zone extending from the surface to a depth of 5 km. We demonstrate the fidelity of the technique by modeling the strong-motion recordings from the Imperial Valley, Loma Prieta, Landers, and Northridge earthquakes.

Hybrid Broadband Ground-Motion Simulations: Combining Long-Period Deterministic Synthetics with High-Frequency Multiple S-to-S Backscattering

Abstract We present a new approach for computing broadband (0–10 Hz) synthetic seismograms by combining high-frequency (HF) scattering with low-frequency (LF) deterministic seismograms, considering finite-fault earthquake rupture models embedded in 3D earth structure. Site-specific HF-scattering Green’s functions for a heterogeneous medium with uniformly distributed random isotropic scatterers are convolved with a source-time function that characterizes the temporal evolution of the rupture process. These scatterograms are then reconciled with the LF-deterministic waveforms using a frequency-domain optimization to match both amplitude and phase spectra around the target intersection frequency. The scattering parameters of the medium, scattering attenuation η s , intrinsic attenuation η i , and site-kappa, as well as frequency-dependent attenuation, determine waveform and spectral character of the HF-synthetics and thus affect the hybrid broadband seismograms. Applying our methodology to the 1994 Northridge earthquake and validating against near-field recordings at 24 sites, we find that our technique provides realistic broadband waveforms and consistently reproduces LF ground-motion intensities for two independent source descriptions. The least biased results, compared to recorded strong-motion data, are obtained after applying a frequency-dependent site-amplification factor to the broadband simulations. This innovative hybrid ground-motion simulation approach, applicable to any arbitrarily complex earthquake source model, is well suited for seismic hazard analysis and ground-motion estimation.

Hybrid Broadband Ground-Motion Simulation Using Scattering Green's Functions: Application to Large-Magnitude Events

We calculate near-source broadband (0-10 Hz) seismograms by combin- ing low-frequency three-dimensional (3D) finite-difference seismograms (0-0.5 Hz) computed in a 3D velocity model using site-specific scattering Green's functions for random, isotropic scattering media. The scattering Green's functions are convolved with a slip-rate function to form local scattering operators (scatterograms), which constitute the high-frequency scattered wave field. The low-frequency and high- frequency scatterograms are then combined in the frequency domain to generate broadband waveforms. Our broadband method extends the Mai et al. (2010) approach by incorporating dynamically consistent source-time functions and account- ing for finite-fault effects in the computation of the high-frequency waveforms. We used the proposed method to generate broadband ground motions at 44 sites located 5-100 km from the fault, for Mw 7.7 earthquake scenarios (TeraShake) on the south- ern San Andreas fault, which include north-to-south, south-to-north, and bilateral rupture propagation from kinematic and spontaneous dynamic rupture models. The broadband ground motions computed with the new method are validated by com- paring peak ground acceleration, peak ground velocity, and spectral acceleration with recently proposed ground-motion prediction equations (GMPEs). Our simulated ground motions are consistent with the median ground motions predicted by the GMPEs. In addition, we examine overturning probabilities for 18 precariously balanced rock sites (PBR). Our broadband synthetics for the Mw 7.7 TeraShake sce- narios show no preferred rupture direction on the southern San Andreas fault but are inconsistent with the existence of PBRs at several of the sites analyzed.

A Characteristic Rupture Model for the 2001 Geiyo, Japan, Earthquake

In this study we present a characteristic kinematic rupture model for an intraslab earthquake of the type of the 2001 Geiyo earthquake. The procedure for developing the characteristic rupture model follows the recipe developed by Irikura and Miyake (Proceedings of the 8th US National Conference on Earthquake Engineering, San Francisco, 2006) with a few modifications. We used the functional form of Nakamura and Miyatake [Zisin (J Seism Soc Jpn), 53, 1–9, 2000] to model the spatial and temporal variability of the slip rate function. In our procedure the earthquake source is specified by the kinematic description of the fault model that incorporates spatial heterogeneity in slip and rise time and constant rupture velocity. In the proposed characteristic model the asperity locations and rupture initiation point were the only parameters that were constrained by the available earthquake rupture models of the target earthquake. The quality of the characteristic rupture model was assessed by comparing recorded and synthetic ground motion time histories from the 2001 Geiyo earthquake calculated with a standard broadband (0.1–10 Hz) ground motion simulation technique. Our analyses show that the characteristic rupture model performs well in reproducing the recorded ground motion, in spite of its simple representation of the fault geometry and kinematic rupture complexity. The analyses of ground motion sensitivity to relative location of asperities, and their stress drop contrast suggest that the overall ground motion goodness of fit remains the same at short periods, but decreases slightly at periods longer than 1 s. We suspect that, due to the depth of the intraslab source (40–50 km), the higher-frequency ground motions are relatively insensitive to the details of the slip distribution and slip contrast. On the other hand, even for intraslab events, the lower-frequency motions are influenced by rupture directivity effects and slip distribution.