Improvements to detection capability by cross-correlating for similar events: a case study of the 1999 Xiuyan, China, sequence and synthetic sensitivity tests

Abstract

Comparisons are made of the performance of a correlation detector compared to a standard short-term average window/long-term average window (STA/LTA) detector for 90 events in the 1999 Xiuyan, China, earthquake sequence. Triggers on three component data verify independent detections to the nearest sample. Unrelated signals that trigger above a threshold do not align on the three components and do not constructively interfere when the cross-correlation traces are stacked or averaged. Semi-similar events due to less than perfect matches arising from substantial mechanism differences can provide useful detections. Synthetic tests on 78 028 focal mechanisms indicate that statistically significant detections are still triggered for strike, dip and rake variations as large as 55°. The correlation detector finds 90 out of 90 or 100 per cent of the events whereas a STA/LTA detector finds 10 out of 90 or 11 per cent. This represents a 1.3 magnitude unit reduction in detection threshold for these events or nearly a factor of 20 improvement.