Validation on the Rate of Rupture Propagation of the 2001 Kunlun, China (Ms=8.1) Earthquake from Seismological and Geological Observations

We determine the fault slip distribution along the nearly 400 km long fault of the 2001 Kunlun earthquake (Ms=8.1) by inverting the teleseismic waveforms, and using geological and using geological and remote sensing field observations as additional constraints. The determined spatial slip distribution was divided into five segments according to geological field observations. Forward modeling of the regional surface waves was performed to obtain an estimate of the variation of the rate of rupture propagation during faulting. For that purpose, the regional 1-D velocity structure was carefully constructed from data from six regional stations for three events with magnitudes of 5.1 - 5.4, distributed along the Kunlun fault. Our results show that the initial rupture of the 2001 Kunlun earthquake was almost purely strike-slip with a rupture velocity of 1.9 km/sec, increasing to 3.5 km/s in the second fault segment, reaching a rupture velocity of 6.2 km/s in the third segment, and then 5.9 km/s in the fourth segment, where the maximum offset with a broad fault zone was observed. After that, the rupture velocity decelerated to a value of 3.3 km/s in the final segment. Slip on the fault was concentrated between the surface and a depth of 10 km. The significant variation of the rupture velocity and observed fault breaks might indicate the variations of the strength within the Kunlun fault, which are related to the fault geometry and strength of the crust.