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Characterization of Fault Zones by Analysis of Aftershock waveform Data

Journal of Earth Science 2009年第6期20卷 985-994页

作者：李红谊李松林赖晓玲 Key Laboratory of Geo-detection (China University of Geosciences Beijing)Ministry of Education School of Geophysics and Information Technology China University of GeosciencesBeijing Geophysical Prospecting Center China Earthquake Administration

Large property contrasts between materials in a fault zone and the surrounding rock are often produced by repeating earthquakes. Fault zones are usually characterized by fluid concentration, clay-rich fault gouge, increased porosity, and dilatant cracks. Thus, fault zones are thought to have reduced seismic velocities than the surrounding rocks. In this article, we first investigated the synthetic waveforms at a linear array across a vertical fault zone by using 3D finite difference simulation. Synthetic waveforms show that when sources are close to, inside, or below the fault zone, both arrival times and waveforms of P-and S-waves vary systematically across the fault zone due to reflections and transmissions from boundaries of the low-velocity fault zone. The arrival-time patterns and waveform characteristics can be used to determine the fault zone structure. Then, we applied this method to the aftershock waveform data of the 1992 Landers M7.4 and the 2008 Wenchuan （汶川） M8.0 earthquakes. Landers waveform data reveal a low-velocity zone with a width of approximately 270-370 m, and P-and S-wave velocity reductions relative to the host rock of approximately 35%-60%; Wenchuan waveform data suggest a low-velocity zone with a width of approximately 220-300 m, and P-and S-wave velocities drop relative to the host rock of approximately 55%.

关键词： waveform characteristics seismic-wave propagation fault zone structure.

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Earthquake Source, Path and Site Effects

Earthquake Source, Path and Site Effects

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第四届世界华人地质科学研讨会

作者： Shengzao Chen Geomatrix Consultants Inc. 2101 Webster St 12th FL Oakland CA94612 USA

＜正＞Source radiation, path anelastic scattering, and she responses constitute a major component of ground motion seismology. Observed spectra generally reflect the combined effects of the source nucleation, along with whole-path and local attenuation and amplification. To separate source spectra from path and site responses, both of these effects must be removed from Fourier spectra computed from strong motion records. For this purpose, effects of geometrical spreading, anelastic scattering （whole-path） attenuation （1/Q）, and site effects have been extensively studied over different tectonic regions around the world. Attenuation effects include geometric spreading, anelastic attenuation, and near-surface attenuation. There are also crustal amplification effects, which can be significant where mere exists a strong velocity contrast or gradient Among the tectonic regions studied, it is found that source spectra are approximately independent of region, distance, and depth when path and site effects are properly removed Kappa values vary regionally. The lowest kappa value corresponds to the hard rock sites in a stable intraplate environment （for example, eastern North America）, while generally higher kappa values correspond to the site conditions in active tectonic environments such as Japan, Mexico, British Columbia （western Canada）, California, and Turkey.

关键词： strong ground motion earthquake source seismic-wave propagation attenuation crustal structure focal depth.

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