Coseismic Slip Distribution of the 2001 Kunlun Mountain Pass West Earthquake Constrained by GPS and Insar Data

Abstract

AbstractThe rupture process of the 2001 Ms 8.1 Kunlun Mountain Pass West earthquake was quite complex. Studies on its coseismic rupture distribution using different datasets, methods, and models have so far produced rather different results. We use coseismic displacement data from the Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar (InSAR) measurements before and after the earthquake to invert for its rupture distribution. We test multiple model parameters, and provide a more detailed result than previous studies under an optimized smoothing constraint. The modeling process consists of three steps: First, assuming a vertical fault plane we obtain an optimal smoothing constraint for the solution based on balancing a trade‐off between the solution resolution and model misfit. Second, we vary dipping angles of fault segments to search for optimal dipping angles in data fitting. Finally, we adopt the fault smoothing constraint and dipping angles obtained from previous two steps and invert for the coseismic rupture distribution. Comparing with previous studies, our results agree better with the field survey results on horizontal surface offsets. We also find that the coseismic displacement amplitudes are asymmetric across the seismic fault, with the displacements south of the fault about 10%~20% larger in amplitude than that north of the fault. This observation can be explained by the fault dipping 80°~81° to the south. We also demonstrate for the first time that a left‐stepping fault about 50 km long in between the west end of the East Kunlun fault and the east end of the Sun Lake fault absorbed 0.1~0.2 m of normal faulting, and the Kunlun Pass fault absorbed about 0.8 m thrust faulting. The seismic moment release is estimated as 9.3 × 1020 N·m, corresponding to a Mw 8.0 earthquake.