Mapping the Spatial Distribution of the Origin of High Frequency Seismic Energy from Extended Faults

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This research is to extend the study of earthquake fault rupture surfaces to higher frequency radiation, above 3 hertz. In this range, waveform inversion has proven impractical due to earth's complexities and a procedure has been developed using seismic wave energy envelopes. The technique locates high frequency energy sources on extended faults by means of strong motion seismograms. Preliminary results indicate that the high frequency energy sources are located along or near the boundaries of large slip zones. This supports the hypothesis that high frequencies are most strongly generated from rupture stopping areas or areas with large slip variation, which has implications for earthquake hazard estimates. The current work will extend the analysis to more earthquakes. This research is a component of the National Earthquake Hazard Reduction Program.