【摘要】 根据前人对唐山地震破裂分布、地壳波速和粘性结构的研究,考虑局部应力场、孔隙流体压力和断层附近软介质的影响,计算了唐山地震产生的,投影到后续大余震断层面和滑动方向上的库仑破裂应力变化.结果表明,随后发生的滦县地震和宁河地震均发生在唐山地震产生的库仑破裂应力变化为正的区域.为研究唐山地震、滦县地震和宁河地震对后续小震的触发作用。根据前人对该地区构造应力场和地震破裂分布的研究,假定构造应力量值为10 MPa。求得了震源附近各处可能的小震震源机制.将上述3次地震产生的应力变化投影到可能的小震破裂面和滑动方向上.发现唐山地震、滦县地震和宁河地震产生的正库仑破裂应力变化的"蝴蝶"形分布与后续小震发生的空间分布具有较好的一致性.95%的余震发生在库仑破裂应力变化增加的区域,说明唐山地震序列中前面的大震对后续小震的发生起到了调制作用.该研究结果对大震后余震的危险性快速评估具有一定意义.如果大地震发生后能够快速确定详细的破裂分布和震源区域详细断层及滑动特性资料,本文方法可用来预测未来大余震的发震位置.更多还原

【Abstract】 We calculated the Coulomb failure stress change generated by the 1976 Tangshan earthquake and projected the stress change onto the fault planes in slip directions of the large follow-up aftershocks.A visco-elastic media is as- sumed in the model.Results of previous studies on co-seismic slip distribution of the Tangshan earthquake,and on crustal velocity and viscosity structures, are used for constraining the model.Effect of the local pore fluid pressure and impact of soft medium near the fault are also considered.Our result shows that the subsequent Luanxian and Ninghe aftershock occurred in the region of in- creased Coulomb failure stress produced by the Tangshan mainshock.To study the triggering effect of the Tangshan,Luanxian,and Ninghe earthquakes to the follow-up small earthquakes,we firstly evaluated the possible focal mechanisms of small earthquakes according to the regional stress field and co-seismic slip distributions derived from previous studies,and assumed a regional tectonic shear stress of 10 MPa.By projecting the stress changes generated by the above three earthquakes to the possible fault planes in slip directions of small earth- quakes,we found that the "butterfly" distribution pattern of increased Coulomb failure stress is consistent with the spatial distribution of follow-up aftershocks, with 95% of them occurred in the region of increased Coulomb failure stress. This result indicates that the former large earthquakes modulated occurrences of follow-up earthquakes in the Tangshan earthquake sequence.This result is of some significance in rapid assessment of aftershock hazard after a large earth- quake.If detailed co-seismic slip distribution on a seismogenic fault and the me- chanical feature of nearby faults can be rapidly determined after a large earth- quake,our approach may be used to predict the locations of large aftershocks.更多还原