Chapter 2 Geometry and Slip Distribution of Coseismic Surface Ruptures Produced by the 2001 Kunlun, Northern Tibet, Earthquake

Abstract

This chapter presents a case study of deformation structures of the coseismic surface ruptures produced by the 2001 Mw 7.8 Kunlun earthquake along the strike-slip Kunlun Fault in northern Tibet. Field investigations, seismic data, and interpretations of high-resolution remote sensing images reveal the geometric and deformational characteristics and strike-slip offset distribution of the 2001 Kunlun coseismic surface ruptures. The coseismic surface ruptures are mainly composed of numerous distinct shear faults, echelon extensional cracks, and mole tracks, which are concentrated on a deformation zone ranging from a few meters up to ∼500 m in width and extending for 450 km along the western segment of preexisting active Kunlun Fault striking E-W to WNW-ESE. Structural features and focal mechanism solutions reveal that the earthquake had a nearly pure strike-slip mechanism. The 2001 coseismic strike-slip offsets measured in field and from 1-m-resolution IKONOS and 0.61-m-resolution QuickBird images range from 2 m up to ∼16 m, generally 3 to 8 m. The spatial distribution pattern of strike-slip offsets observed immediately after the 2001 earthquake in the field coincides well with that obtained from high-resolution remote sensing images and seismic inversion results. Both the rupture length and maximum displacement are the largest among the coseismic surface rupture zones ever reported in intracontinental earthquakes. Field evidence, seismic inversion results, and interpretations of high-resolution remote sensing images demonstrate that the geometric characteristics and the temporal and spatial displacement distributions of the coseismic surface ruptures are constrained by the preexisting geological structures of the active strike-slip Kunlun Fault.