Characteristics, Geometry, and Segmentation of the Surface Rupture Associated with the 14 April 2010 Yushu Earthquake, Eastern Tibet, China

Abstract

On the morning of 14 April 2010, the M s 7.1 Yushu earthquake struck the eastern Tibet Plateau and an M s 6.3 aftershock followed west‐southwest of the mainshock epicenter one and a half hours later. The Yushu earthquake occurred on the northwestern continuation of the Ganzi–Xianshuihe fault zone and reactivated two segments of the fault. Ruptures associated with Yushu earthquake span a zone ≈70 km long, extending from south of Jielong in the west to south of Gyegu (Yushu) in the east. Detailed mapping of the surface rupture zone shows that it consists of two strike‐slip segments, the western and eastern segments, separated by the Longbao Lake step‐over (pull apart) basin. Our analysis suggests that the 18‐km‐long western segment of the surface rupture south of the Longbao Lake basin may have been associated with the M s 6.3 aftershock. The eastern rupture segment, which is inferred to be associated with the mainshock, is 32 km long. The main surface rupture can also be divided into two sections, with a 2‐km‐long gap between them. The surface rupture exhibits left‐lateral slip and is localized in a zone about 50 m wide along the present‐day trace of the Yushu fault. A single break, without splays or branching traces, characterizes most of the surface rupture zone. The observed magnitudes of surface displacement are typically 0.5–1 m with a maximum slip of ≈2 m. Both field observations and seismic inversion results suggest, rupture of M s 7.1 Yushu earthquake nucleated near the Longbao Lake step‐over basin in the west, propagated unilaterally eastward, and terminated within the east segment margin of the Yushu fault.