Seismic Source Characterization in Asia
LOS ALAMOS NATIONAL LAB NM
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A significant challenge of modeling small-to-moderate- size seismic sources is the necessity of relying on short-period signals with long travel paths that are significantly sensitive to earth structure along the path. When the path effects are unknown or difficult to account for, we must rely on components of seismic signals that are minimally dependent on the structure. Although regional surface-wave phase is strongly influenced by structure, surface wave amplitude spectra can be modeled adequately with relatively simple models, and these spectra carry valuable information on source character and depth. Our efforts build on existing seismic source analysis techniques. We directly model regional seismograms where possible but combine those time-domain observations with surface wave amplitude spectra at more distant regional stations. We have used regional seismic data to estimate seismic moment tensors and event depths for characterization of seismic sources in Asia. For larger events in the study greater than magnitude 5 we have successfully included long-period approximately 40 seconds period body-wave trains that can be modeled reliably using simple stratified earth models into our grid search for strike, dip, rake, moment, and depth. Our main focus is to use regional seismic data to estimate seismic source mechanisms, moments, and event depths to characterize seismic sources in Asia. A complete catalog of regionally estimated seismic moments, source mechanisms, and depths will be a useful tool for magnitude calibration and regional characterization. Recent work has suggested possible bias in Harvard CMT moment estimates for events in central Asia Patton, 1998. Thus, we are particularly interested in constraining seismic moments, which are critical for calibrating regional magnitude scales with global catalogs, and in improving depth estimates for Asian events.