Improving Magnitude Detection Thresholds Using Multi-Station Multi- Event, and Multi-Phase Methods

摘要

We report on the results of both a semi-empirical analysis and a case study in Xiuyan, China, that demonstrated that a correlation detector can lower magnitude detection thresholds by over one full unit for similar events as compared to a standard STA/LTA detector. 90 out of 90 events (100%) were detected by cross correlation for the case study whereas a procedure like the pIDC employs detected only 11%. We found that less than perfect matches still provided useful detections due to location, focal mechanism, and magnitude differences. Events with magnitude differences as large as 2.3 and 3.3 were shown to produce detection spikes on the correlation traces. Further work applied the correlation techniques on a larger scale to 5,000 events at Parkfield, California, and 19,000 events in and near China. We are attempting to see how broadly applicable correlation methods can be applied to different tectonic settings and for what percentage of the seismicity. 111 million correlations were performed on Lg-waves for the events in China at 363 stations. Final results indicate two thirds of the 19,000 events can be detected by cross correlation using this relatively sparse regional network. The full magnitude unit reduction in detection threshold is confirmed on a large scale in China and Parkfield.