Coseismic and postseismic deformation associated with the 2003 Chengkung, Taiwan, earthquake

We use GPS-derived coseismic and postseismic displacements of the 2003 M-w 6.8 Chengkung, Taiwan, earthquake to examine seismogenic behaviour of the southern Longitudinal Valley. We invert for fault slip on the Chihshang fault, a segment of the Longitudinal Valley fault, based on a simplified layered earth model and a listric-shape fault geometry. Our model infers that maximum coseismic slip of about 0.72 m occurred at a depth of 15 km. Conversely, postseismic slip of about 0.1 m over a 157 d period mainly occurred at depths less than 10 km. We find an anticorrelation between coseismic and postseismic slip distributions. However, the depth profiles of seismicity before and after the main shock are very similar and both show the peak seismicity at 15-25 km depth, consistent with the depth range of large coseismic slip. The potency distribution at depth reveals a coseismic slip deficit at shallow depths, which is compensated by postseismic and interseismic creep associated with the Lichi Melange. Aseismic slip is an important component of the slip budget on the Chihshang fault. According to the historic earthquake records, interseismic slip rate and coseismic slip on the Chihshang fault, the recurrence interval of this type of event is between 12 and 36 yr. We use a rate-dependent friction model of afterslip to infer the frictional parameter, d tau(ss)/dlnV = 0.03-0.5 MPa, at shallow depths on the Chihshang fault. Assuming effective normal stress of 100 MPa at 5 km depth, the rheological parameter, a = partial derivative mu/partial derivative ln V, is about 3 x 10(-4)-5 x 10(-3), which is in good agreement with laboratory experiments.