从库仑破裂应力和余震分布角度探讨汶川地震和芦山地震的关系

摘要

本文以龙门山及周边地区为研究对象,考虑区域地质构造差异、主要活动断裂带、地表附加重力影响,建立能反映地表起伏和岩石圈分层结构的龙门山地区三维粘弹性有限元模型.以地壳水平运动速率观测值为约束条件重建研究区现今构造背景应力场,在此基础上分别模拟了汶川地震和芦山地震的发生机理.通过分析同震库仑破裂应力变化与余震空间分布的关系,探讨了2次地震主震对余震的触发作用以及汶川地震对芦山地震的影响.研究表明,汶川地震和芦山地震的余震大部分由其主震触发,汶川地震对芦山地震的余震有约6.78％的触发作用.汶川地震的同震库仑破裂应力在芦山地震主震位置的增加值约为0.016MPa,如果龙门山断裂带南段库仑破裂应力年累积速率按照0.4× 10-3-0.6x 10-3MPa.a-1计算,汶川地震使芦山地震提前了约27-40年.计算还表明汶川地震和芦山地震的发生使鲜水河断裂带南段和虎牙断裂的库仑破裂应力增加,这些断裂带在未来发生地震的可能性增加.%Taking the Longmenshan and its surrounding area as the research area,with consideration of the difference of regional geological structure,the main active fault zone,additional surface gravity,we constructed the 3-D viscoelastic finite element model of the Longrnenshan area with irregular topography and the layered lithosphere structure.Using the observed values of crustal horizontal movement as constraint condition,the present tectonic background stress field in the research area is reconstructed.Based on it,the occurrence of Wenchuan earthquake and Lushan earthquake are simulated respectively.Through the analysis the relationship between coseismic Coulomb stress change and the spatial distribution of aftershocks,the trigger action of main shock to aftershock and the influence of Wenchuan earthquake on Lushan earthquake is investigated.The results show that the most aftershocks of Wenchuan earthquake and Lushan earthquake are triggered by their main shock,and only 6.78％ aftershock of Lushan earthquake is triggered by Wenchuan earthquake.The coseismic Coulomb stress of the location of Lushan earthquake caused by Wenchuan earthquake is about 0.016MPa.Assuming tha the annual cumulative rate of Coulomb stress in the southern segment of the Longmenshan fault zone is 0.4-0.6× 10-3MPa· a-1,the occurrence of Wenchuan earthquake causes the occurrence of Lushan earthquake nearly 27-40 years earlier than it should.Our results also show that the Wenchuan earthquake and Lushan earthquake cause the Coulomb stress increase in the southern segment of the Xianshuihe fault zone and Huya fault,which increases the possibility of earthquake in this area in the future.