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Global variations of stress drop for moderate to large earthquakes

Bettina P. Allmann, & Peter M. Shearer

Published 2009, SCEC Contribution #1194

We investigate the global variation of earthquake stress drops using spectra of about 2000 events of Mb>=5.5 between 1990 and 2007. We use an iterative least squares method to isolate source displacement spectra from travel path and receiver contributions, based on a convolutional model. The observed P-wave source spectra are corrected with a globally averaged <br/>empirical Green's function (EGF) and estimates of near-source attenuation. Assuming a Brune-type source model, we estimate corner frequencies and compute stress drops. Stress-drop estimates for individual earthquakes range from about 0.3 to 50 MPa, but the median stress drop of about 4 MPa does not vary with moment, implying earthquake self-similarity over the Mw=5.2 to 8.3 range of our data. A comparison of our results with previous studies confirms this observation over most of the instrumentally observable magnitude range. While the absolute values of our estimated stress drops depend upon the assumed source model, we identify relative regional variations of stress drop that are robust with respect to the processing parameters and modeling assumptions. We find a dependence of median stress drop on focal mechanism, with higher stress drops for strike slip earthquakes, and also find higher stress drops for intraplate earthquakes compared to interplate earthquakes.

Allmann, B. P., & Shearer, P. M. (2009). Global variations of stress drop for moderate to large earthquakes. Journal of Geophysical Research, 114. doi: 10.1029/2009JB005821.