【摘要】 基于中国地震台网中心2013 MS7.0芦山地震余震数据我们首先确定了余震空间分布范围并根据G-R关系计算了主震后半小时内的完备震级Mc=3.5,并且得到了ML≥3.5和ML≥3.0的地震在2001年至芦山地震前的背景场地震发生率.通过Omori-Ustu经验定律和两种Dieterich模型对芦山地震余震发生率的拟合,我们发现阶梯型Dieterich模型只能模拟p=1的情况,从而造成了模拟曲线与观测数据的差别;前人研究表明震后滑移同样是产生余震的原因,如果假设余震序列由主震静态剪应力Δτ和震后滑移共同作用所产生,我们数值模拟得到的对数型Dieterich模型能够较好地推断余震发生率R随时间t增加而衰减的趋势,能够从物理机制上解释MS7.0芦山地震余震序列衰减指数大于1这一现象.通过对数型Dieterich模型的拟合并结合Andrews的方法,我们还得到MS7.0芦山地震Aσ约为0.155 MPa,ta约为8.4年,这一值与前人研究结果十分接近.更多还原

【Abstract】 Accurately predicting aftershocks decay after the main shock over time is conducive to learn the aftershocks triggering physical mechanism.On the other hand,the predicted duration of aftershocks is also an important aspect of seismic hazard analysis.In this study,by fitting the seismicity decay with both the empirical and physical models,we try to study Lushan earthquake triggering mechanism,and figure out how coseismic stress,afterslip and other parameters affect aftershocks decay.First,based on the seismicity data from the China Earthquake Network Center,the magnitude of completeness Mcfor the early part was estimated using a maximum likelihood procedure.We then compute the observed seismicity decay and fit it with both the empirical andphysical models.By using agrid search method,parameters of predication models could be determinated.The magnitude of completeness Mcfor the early part(~0.02day)was estimated at 3.5using a maximum likelihood procedure.We found that,with the stress step formed Dieterich model,apvalue larger than 1could not be explained,which was in contradiction with empirical observations of p>1aftershock decays.We have shown that by modeling a coseismic step and a postseismic stress change with a constant background stress rate,the Omori exponent larger than one for the MS7.0Lushan Earthquake aftershock sequence could be well explained and fitted.With Andrews′method,we calculated the distributed stress changes on the fault plane,and we inferred Aσ~0.155 MPa,also,the logarithmic stressing Dieterich model predicts a more reasonable aftershocks duration ta~8.4years,which is close to former researchers′result.By showing the merits and limitations of the modified Omori law and the step function formed Dieterich model,we find that the stress step formed Dieterich model cannot explain an Omori law decay with p>1,thus,this physical model may overestimate the aftershock duration.We show that modeling by a coseismic step,apostseismic stress change with a constant background stress rate,the Omori exponent larger than one for MS7.0Lushan earthquake could be explained.更多还原