Investigation on the rupture behavior of the 2001 Kunlun and 1997 Manyi, China, earthquakes: constraints from near field geological data and regional surface wave

We first determine the nearly 400 km long finite-fault slip distribution of the November 14, 2001 Kunlun earthquake (Ms=8.1) by inverting the teleseismic waveforms and using geological field observation as additional constraints. The geological field observations provide well-determined fault geometry and constrain the amount of slip at the surface. We perform forward modeling of the regional surface waves to validate slip distribution obtained by inverting teleseismic body waves. The phase velocity of the regional surface waves is much slower than the teleseismic body wave, which makes it possible to resolve variations in the rupture velocity during faulting. We find that the initial rupture of the 2001 Kunlun earthquake was almost purely in a strike-slip fashion 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 5.9 km/s in the forth 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 on the final segment. The significant variation in rupture velocity indicates differences in the partition of the earthquake fracture energy during faulting. On the other hand, there are no field investigations for the November 8, 1997 Manyi earthquake (Mw=7.6) and the bilateral rupture makes it difficult to estimate the variation in rupture velocity. Therefore, we validate the fault slip model by forward modeling the surface deformation determined by the InSAR. Preliminary waveform inversion suggests that a reversing-dip fault model, which is consistent with geological data, is necessary to improve the waveform fitting. In particular, our model can predict the asymmetry of the ground displacement in the north and south of the fault as shown in the InSAR study. The rupture behavior of these two earthquakes will provide not only implications on tectonic involvement of the Kunlun fault to the eastward extrusion of Tibet, but also the earthquake triggering mechanism along a mature fault system.