库仑应力计算及应用过程中若干问题的讨论——以汶川地震为例

Some aspects in static stress change calculation——case study on Wenchuan earthquake

大地震发生后,估计后续地震发展趋势是人们关心的问题.目前,学术界经常利用大地震造成的库仑应力变化研讨大震对后续地震的影响,但库仑应力的计算和应用中尚有一些问题被忽视而有待探讨.本文修正了传统的库仑应力计算中沿地震破裂面滑动方向计算剪应力变化的近似方法,考虑震后主应力方向可能改变对剪应力变化量计算的影响,对改进方法和传统方法获得的结果进行了对比分析.本文基于龙门山地区背景应力场测量资料,根据不同研究者反演的地震破裂模型,计算了汶川地震造成的静态库仑应力变化,考察了不同地震破裂模型下库仑应力分布差异.在断层面附近,使用改进方法与传统方法计算的库仑应力分布差异相当大;利用多个地震破裂模型计算大地震库仑应力判断大震后余震发展趋势时,要注意破裂模型不确定性对危险性估计的影响.

When a major earthquake occurs, how aftershocks distribute catch the attention of the public. Recently, the concept of Coulomb failure stress is used frequently to study the earthquake triggering of main shock. However, there are some pendent problems in the calculation and application of Coulomb stress. In conventional calculation of Coulomb stress, the shear stress change is approximated to be the changed value along the slip on the rupture of main shock. In fact, the stress orientations may change after the event. It affects the shear stress on ruptures. We improved the formula of Coulomb stress and made comparison. We applied the improved method to Wenchuan earthquake. According to the stress measurement in Longmenshan and the three rupture models, we calculated the static Coulomb stress of Wenchuan earthquake. The results show big differences between conventional and improved calculation around the fault. Our investigation reminds us to concern the uncertainty of the rupture models when we use Coulomb stress to predict the aftershocks.