Investigation of source depths of the 2006 Pingtung earthquake sequence using a dense array at teleseismic distances

Abstract

We determined source depths of 6 major events of the 2006 Pingtung Earthquake sequence by comparing the observed array beams at teleseismic distances with synthetic seismograms for a range of depths. A simple but robust procedure to identify the depth of a seismic event has was developed and successfully demonstrated through its application to the Pingtung Earthquake sequence. This method is theoretically based on the fact that adopting the surface-reflected waveforms at teleseismic distances can eliminate the tradeoff relationship between the source depth and epicenter determination. Accordingly, we utilized high quality seismic records of the Yellowknife Array with our method and found that we did obtain reasonable results; the depths of 6 events previously determined by CWBSN were overestimated except a second large event. This event was a complex source rupture, which occurred on December 26, 12:34 UTC (Mw = 6.9), based upon a detailed examination of near source strong motion seismograms. Combining analyses from near source and teleseismic observations, we suggest that the shallow fault plane rupture progressed deeper during the event. Investigations based on teleseismic and local observations identified different portions of the rupture fault, wherein the CWBSN data constrained the initial onset and the Yellowknife Array resolved the centroid of the rupture.