A Model of In-depth Displacement under Ms8.1 at Kunlun Earthquake with D-InSAR Co-seismic Deformation Field

Abstract

Numerical modeling can be used to obtain geophysical information for earthquake mechanism analysis. During the past decade, differential synthetic aperture radar interferometry (D-InSAR) technology has been applied successfully to research co-seismic field and hypocentral mechanism, which could offer more abundant boundary conditions with higher quality as compared with the conventional methodology of geodetic measurement. This paper reports a model of in-depth co-seismic displacement with this approach. On November 14, 2001, a Ms8.1 earthquake, one of the largest events hitting the Chinese mainland over the past 50 odd years, occurred at the Kunlun Mountains in the northern Tibetan plateau, China. In this model, a co-seismic field is established and a series of hypocentral parameters are extracted on the earthquake applying D-InSAR processing with 2Pass+external DEM mode to 20 pair’s ERS-2 SAR data and combined with field geology investigation as well as GPS observations on permanent stations. D-InSAR co-seismic field shows that the Kunlun Mountain Ms8.1 earthquake produced a 430-kilometer-long surface rupture zone, composed by the western section of Taiyang Lake-Kushuihuan with a length of 30km, the eastern section of Bukadaban Peak-Kunlun Mountain Pass with a length of 350km and a 50km long unbroken step area between the above-mentioned two sections. This rupture zone shows such obvious characteristics as distinct segmentation and a left-lateral slip with little reverse component. The maximum co-seismic sinistral horizontal dislocation is 7.38m, of which 4.30m on the south wall and 3.08m on north wall. The maximum vertical dislocation is 4.0m. By means of Poly3D, a geophysical boundary element method (BEM) developed by Stanford University, and based on the boundary conditions of D-InSAR hypocentral parameter, this paper simulates a 3D distribution of the co-seismic deformation and spatial trend of displacement vector over the shock surface area of 80,000 km2 and its underground areas of 20km in depth. The 3D displacement field shows that the maximum strike displacement Ux occurs at 15km below the surface of the Hoh sai Hu lake east-Yuxi peak segment, with a maximum dislocation of 6.424m, the maximum dip displacement Uy is located 10km below the surface of the Yuxi peak-Kunlun Mountain Pass segment, with a maximum dislocation of 2.067m, and the maximum dip displacement Uz is located 10km below the surface of the Yuxi peak-Kunlun Mountain Pass segment with a maximum dislocation of 3.701m. The simulation displacement vectors indicate that bounded by the almost vertical main rupture plane, the south wall thrusts northward with some subsidence, the north wall moves upwards, the south wall moves from west to east while the north wall does from east to west. As the horizontal offset is dominated by left-lateral vertical displacement, the earthquake is classified as a strike-slip dominant type. Thus it is concluded that the Ms8.1 Kunlun earthquake originated from the Kunlun fault with a set of steep dip, left-lateral and strike-slip reverse faults.