Joint inversion of seismic and geodetic data for the source of the 2010 March 4, Mw 6.3 Jia-Shian, SW Taiwan, earthquake

The 2010 March 4, Jia-Shian (M-w, 6.3) earthquake in SW Taiwan caused moderate damage and no surface rupture was observed, reflecting a deep source that is relatively rare in western Taiwan. We develop finite-source models using a combination of seismic waveform (strong motion and broadband), Global Positioning System (GPS) and synthetic aperture radar interferometry (InSAR) data to understand the rupture process and slip distribution of this event. The rupture centroid source depth is 19 km based on a series of moment tensor solution tests with improved 1-D Green's functions. The preferred fault model strikes 322 degrees and dips 27 degrees to the NE and the mainshock is a thrust event with a small left-lateral component. The finite-source model shows a primary slip asperity that is about 20 km in diameter at a depth range from 22 to 13 km, with peak slip of 42.5 cm, a total scalar seismic moment of 3.25 x 10(18) N m (M-w 6.34) and with an average static stress drop of 0.24 MPa. The rupture velocity of this event is faster than the mid-crustal shear wave velocity in Taiwan, which suggests the possibility of a supershear event which has not been previously observed in Taiwan. Systematic resolution and sensitivity tests are performed to confirm the slip distribution, rupture velocity, the choice of weighting and smoothing for the joint inversions, and the consistency of the slip distribution. The first 24 hours of aftershocks appeared along the upper periphery of the main coseismic slip asperity. Both the mainshock and aftershocks are located in a transition zone where the depth of seismicity and an inferred regional basal decollement increases from central to southern Taiwan. The difference between the current orientation of plate convergence in Taiwan (120 degrees) and the P axis of this event (052 degrees) and nearby measurements of recent crustal strain directions (050 degrees to 080 degrees), as well as the relatively low static stress drop, suggest that the Jia-Shian event involves the reactivation of a deep and weak pre-existing NW-SE geological structure.