The recently proposed hybrid Green's function method is designed to combine the advantages of both deterministic and stochastic approaches to simulating broadband ground motion when records of small events are not available. The method has the flexibility of incorporating complexities in the source, wave path, and localsite effects into strong ground motion simulations. In this article we analyze its effectiveness at simulating near-fault ground motions by comparisons with the empirical source time function method, empirical ground-motion-attenuation relations, and recorded near-fault ground motion. We present a simple model for introducing the effect of the radiation pattern to the stochastic Green's functions in the intermediate frequency range (1-3 Hz). The numerical test results of the method and the generally good agreement between simulated and recorded ground motion from the 17 January 1995 Kobe earthquake shown in this study indicate that the technique has the capability of reproducing the main characteristics of near-fault ground motion.

The three‐dimensional (3D) S‐wave attenuation (Qs) structure beneath the Kanto plain, where the Pacific and Philippine Sea plates subduct, was estimated using strong‐motion records of the K‐NET and KiK‐net. In addition to several low‐Qs zones corresponding to the volcanic front, a large NW–SE trending low‐Qs zone is estimated under the non‐volcanic Kanto area at depths of 20–60 km. This zone corresponds to a previously identified low‐velocity (both Vp and Vs) zone with a high Poisson's ratio at 40‐km depth; it further indicates a wedge immediately above the subducting Philippine Sea plate. Predicted seismic ground motions using the estimated 3D attenuation structure is very similar to the actually recorded by recent earthquake on July 2005 (M = 6).

Over 200 peak amplitudes of strong motion were observed at distances of less than 250 km from the fault during the 1995 Hyogo-ken Nanbu (Kobe) earthquake. We analyzed the attenuation of the peak-ground acceleration and velocity as a function of distance and geological site conditions. The observed peak amplitudes agree well with those predicted by an empirical attenuation relation that was developed for Japanese earthquakes. This demonstrates that on average the peak amplitude of the ground motion generated by this damaging earthquake did not exceed the level predicted by the empirical attenuation relation. We found a significant effect of the surface geology on the observed ground-motion peak amplitude. In particular for soft-soil sites, located near the fault, the peak-horizontal acceleration decreases rapidly with distance as a result of the nonlinear response of soils. In order to take into account the effect of the site conditions we introduced correction factors to the existing attenuation relation. This resulted in a significant reduction of the residuals between the predicted and observed peak amplitudes. Based on the attenuation relation corrected for the site condition effect we generated a map of horizontal peakground acceleration in the Kobe and Osaka area for the Kobe earthquake. The area of simulated large ground motion agrees well with the severe damage zone of intensity VII, JMA scale.

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The three-dimensional attenuation structure of the Japanese islands and site amplification factors are obtained by simultaneous inversion of strong motion records recorded by many acceleration seismometers, i.e. JMA87-type seismometers and the Kyoshin-Net (K-NET) seismometers, almost uniformly distributed in Japan. The result shows that the Pacific slab is high-Q and that the frequency dependence of Q values is expressed as f0.75. We classified all stations into 5 groups by ground conditions mainly on the basis of S-wave logging data and obtained the site amplification factor for each group. The result shows that the frequency band where large amplification factors are obtained by inversion well agrees with the predominant frequency calculated from S-wave velocity data. abnormal distributions of seismic intensities, J. Fac. Sci., Hokkaido Univ. ser. VII, 2, 359-374.