Abstract:

We investigated the seismotectonics of the Yushu Ms7.1 earthquake by relocating the 1670 earthquakes in its sequence from April 11to September 15, 2010 using the double difference algorithm. Most of the relocated hypocentral depths are between 0 and 15 km. The relocated Ms7.1 mainshock occurred at the segment without surface rupture, while the aftershocks distribute along the surface rupture zone to its two sides in a linear pattern. At the northwestern end of the seismic belt without surface rupture, the aftershocks formed a wide fault nearly perpendicular to the main seismic belt. The seismic source rupture process delineated by the aftershocks is to be the bilateral rupture propagation contrast to the result of seismic rupture inversion as the unilateral rupture. The focal mechanism solutions of the mainshock and some large aftershocks suggest that the seismic faulting along the segment with surface rupture to be pure sinistral strike slip, whereas to the northwestern end, the rupture mechanism might be different from that of the mainshock, the wide seismic belt there might be formed by a conjugate rupture. It can be concluded that the aftershocks occurred after a time period were triggered in the process of stress adjustment, and not constrained inside the rupture zone created by the mainshock.

Key words: Yushu earthquake sequence, earthquake relocation, seismotectonics, double difference algorith
m, seismic source rupture