Ms8.0汶川地震断层的应力状态以及对余震危险性的影响

利用中国地震局在汶川地震前后对四川盆地以及龙门山断裂进行的水压致裂绝对应力测量数据、近断层强震记录、以及由美国USGS公布的包括地震矩和地震波能量等在内的远场震源参数解,从简单断层模型出发,应用地震能量分配原理和库仑摩擦准则,初步估算和判断了2008年Ms8.0汶川地震断层破裂过程和震源参数,以及滑移弱化模型下应力变化...

The state of stress of the Ms8.0 Wenchuan earthquake faulting and its implication to the aftershock hazard

With an integration of in-situ borehole strain-meter data recorded at the Central Longmenshan Fault Zone, seismological observations, including the near-fault strong motion records, and fault slip inversion given by worldwide earthquake research groups, we have tried to investigate earthquake faulting processes and source parameters related to the M_S8.0 Wenchuan faulting processes based on the fault mechanic theory. In order to put different data sets together for analyzing and interpretation purposes, Coulomb failure criterion and earthquake energy partition principle have been used in the determination of the strength and state of stress on the fault by involving the slip-weakening frictional model. Strong motion records from Qingping station, the nearest location to the main fault (about 5 km), has been used to quantitatively estimate the averaged dynamic stress drop during fault rupture. The primary results show that, for the Wenchuan main event, the seismic radiation efficiency and seismic efficiency are 36% and 14%, respectively, the critical slip distance D_c is about 0.47 m, and the fracture work and relaxation work are about 1.29×10¹⁶ J and 1.13×10¹⁶ J, respectively. The relaxing work remained inside the fault zone is about the same order as the total radiated seismic energy from the main shock. We present a simple model to predict the size and time length of aftershock sequences based on the elastostatic mechanism and regional deformation model. We propose that, if the faulting mechanism of the aftershocks inside the main fault zone obeys the same energy partition process of the Wenchuan main shock, the largest aftershock in which the radiated energy could by release by remained visco-elastic relaxing work inside the fault zone should be less than the energy released by a M_S6.9 event or much more smaller events will occur later on, and the aftershock sequences within the slowly deforming region are predicting to be significantly longer than decade typically observed at rapidly loaded plate boundaries. This infers that the aftershock sequences after the Wenchuan main shock will continue for many decades based on the current aftershock activity patterns.