Slip partition of the 26 December 2006 Pingtung, Taiwan (M 6.9, M 6.8) earthquake doublet determined from teleseismic waveforms

Abstract

Teleseicmic vertical P waves of an earthquake doublet occurring on 26 December 2006 offshore southwestern Taiwan are analyzed to recover spatial slip distribution. Ground-displacement records for period 0.01 - 0.5 Hz are inverted using linear inversion for finite fault analysis. Waveform inversion results show that a dual segment fault of different strike is necessary for the first event to explain teleseismic waveforms. The trend in fault geometry, thus, inferred was coincidentally consistent with the bathymetry in the fault rupture area, suggesting the possible tectonic structure controlling fault propagation. Both earthquakes show larger slip in the asperities near the hypocenter and there are two main asperities of similar moments. The first event ruptured along a high angle eastern dipping plane while the second event ruptured along a low-angle western dipping fault plane. The spatial distribution of the Pingtung earthquake doublet shows a compensative and conjugate relationship, and the seismic moments of the earthquake doublet were 2.7 × 1026 and 1.8 × 1026 dyne-cm, respectively. The stress drops corresponding to the asperities of the two earthquakes have values of 3 to 4 bars, individually, similar to the values observed in other subduction zones.