Tectonic Block Attribution of the Wenchuan and Yushu Earthquakes Distinguished by Focal Mechanism Types

Abstract

AbstractThe November 14, 2001 Mw7.8 Kunlun Mountain Pass earthquake, the March 21, 2008 Mw7.2 Yutian earthquake and the May 12, 2008 Mw7.9 Wenchuan earthquake all occurred in the middle of Tibet Plateau and formed a new seismicity group. The epicenters of the Kunlun Mountain Pass earthquake and Wenchuan earthquake are located at the northern and eastern boundary of the Bayan Har Block, respectively and the Yutian earthquake at the western end of it. GPS observational data indicate that this block moves to east. The rupture characteristics of the three large earthquakes in different parts of the block suggest the mechanical consistency of the Bayan Har block motion. The intensity and frequency of Yutian aftershocks significantly increased before the main shock and the stronger aftershocks of the Wenchuan earthquake, which proves that there is an internal relation between the three large earthquakes. The April 14, 2010 Mw6.9 Yushu earthquake, the November 19, 1996 Mw6.9 Karakorum Mountain earthquake and the November 08, 1997 Mw 7.5 Mani earthquake all occurred on the southern boundary of the Bayan Har block, and their focal mechanisms are consistently left‐lateral strike slip, which were caused by the eastward motion of the Qiangtang block and formed a new strong earthquake group. The results show that the block has the character of rigid body motion which is the common origin of the two large earthquake groups.