Characteristics of strain release before moderate-strong earthquakes in Yunnan region

Referring to the earthquake catalogues produced by the Yunnan Regional Seismic Network，and setting the seismic strain energy as a scale of the seismic energy release，this paper conducts a nonlinear simulation for the precursory earthquake-sequences based on the accelerating strain release model. In the period from 1966 to 2013，115 earthquakes with M_S≥5.0 occurred in Yunnan region. Among them，79 events are characterized by accelerating strain release，accounting for 69%. And 28 events are featured as decelerating strain release，accounting for 24%. The strain releases of the rest eight events accounting for 7% fail to show the features of acceleration or deceleration due to the less seismic data. As to the precursory earthquake sequences whose main shocks belong to the single-shock type，the ones whose earthquake strain releases are accelerating，or the ones lacking seismic data，are far more than the ones whose strain releases are accelerating. As to the precursory earthquake sequences whose main shocks belong to the strike-slip type，the ones whose earthquake strain releases are accelerating are 15% more than the ones whose main shocks belong to the normal-fault type，or 15% more than the thrust-fault type ones. The searching radius has an inverse relation with the duration of the precursory earthquake sequence. The simulated results for the precursory earthquake-sequences indicate that the error of the main shock’s magnitude is ±0.30，and the error of the main shock’s occurrence time is ±0.5 year.