Rate-and-state friction properties of the Longitudinal Valley Fault from kinematic and dynamic modeling of seismic and aseismic slip

The Longitudinal Valley Fault (LVF, Taiwan) is a fast-slipping fault (∼5 cm/yr), which exhibits both seismic and aseismic slip. Geodetic and seismological observations (1992–2010) were used to infer the temporal evolution of fault slip. This kinematic model is used here to estimate spatial variations of steady state velocity dependence of fault friction and to develop a simplified fully dynamic rate-and-state model of the LVF. Based on the postseismic slip, we estimate that the rate-and-state parameter (Formula presented.) decreases from ∼1.2 MPa near the surface to near velocity neutral at 19 km depth. The inferred (a − b) values are consistent with the laboratory measurements on clay-rich fault gouges comparable to the Lichi Mélange, which borders the LVF. The dynamic model that incorporates the obtained (Formula presented.) estimates as well as a velocity-weakening patch with tuned rate-and-state properties produces a sequence of earthquakes with some realistic diversity and a spatiotemporal pattern of seismic and aseismic slip similar to that inferred from the kinematic modeling. The larger events have moment magnitude (M_w ∼6.7) similar to the 2003 Chenkung earthquake, with a range of smaller events. The model parameterization allows reproducing partial overlap of seismic and aseismic slip before the earthquake but cannot reproduce the significant postseismic slip observed in the previously locked patch. We discuss factors that can improve the dynamic model in that regard, including the possibility of temporal variations in (a − b) due to shear heating. Such calibrated dynamic models can be used to reconcile field observations, kinematic analysis, and laboratory experiments and assess fault behavior.