英文摘要
The roughly east-west sinistral strike-slip Kunlun fault, one of the faults that accommodates the eastward extrusion of Tibet plateau, is an example of large scale slip partitioning in the continental crust. Since 1937, five large (M>7) earthquakes have occurred along different segments of the Kunlun fault, and all show distinct left-lateral strike-slip motion. In this study, we utilize most of the available data, including seismological, geological and InSAR data, to analyze the rupture properties of the two recent large earthquakes on the Kunlun fault the 1997 Manyi earthquake and the 2001 Kunlun earthquake. Then, we will discuss the stress transfer on the Kunlun fault and the relationship between the fault and the regional tectonics. The comprehensive studies by using seismological, geological and InSAR data allow us to have a complete investigation on fault geometry and rupture characters.
We first determine the nearly 400 km long finite-fault slip distribution of the 2001 Kunlun earthquake 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. Then, forward modeling of regional surface waves was performed to estimate the variation of the speed of rupture propagation during faulting. We find that the rupture velocity peaked at around 6.0 km/s (supershear velocity, but not exceeding P-wave velocity) in the third and fourth segments (S-3 and S-4), where the maximum offset with a broad fault zone was observed. The significant variation in rupture velocity indicates differences in the partition of the earthquake fracture energy during faulting. On the other hand, the bilateral rupture and the nearly vertical dipping make it difficult to determine the optimal fault model of the 1997 Manyi earthquake. However, the high resolution and wide coverage InSAR data helps to identify the ground deformation variations derived from the different fault slip models. The preferred fault model of the 1997 Manyi earthquake is that the west segment dipps to the north and the east segment dipps to the south. This is consistent with fault geometry of the 2001 Kunlun earthquake, which is dipping to the south for all segments. The Coulomb stress transfer of the five large earthquakes and the spatial and temporal revolution of the earthquake sequence on the fault 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.
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