1947年达日M7.7地震对巴颜喀拉块体边界断裂应力影响的数值模拟

Influence of the 1947 Dari M 7.7 earthquake on stress evolution along the boundary fault of the Bayan Har block:insights from numerical simulation

1947年达日7.7级地震是发生在巴颜喀拉块体内部的一次强震,该地震在块体边界断裂带应力演化中的作用,在以往的研究中多被忽略.本文通过构建巴颜喀拉块体东部及邻区三维黏弹性有限元模型,考虑达日地震的同震位错与震后黏弹性松弛效应,分析该地震的发生引起巴颜喀拉块体边界断裂带上的库仑应力变化.结果表明:达日地震除造成达日断裂破裂段两端相邻未破裂段显著的库仑应力增加外(>1.0×10^(6) Pa),同时造成龙日坝断裂中-北段、东昆仑断裂中西段、龙门山断裂中-北段、马尔康断裂、鲜水河断裂中-南段和甘孜—玉树断裂西段同震库仑应力的增加,最大达1.4×10^(4) Pa.相反,也造成东昆仑断裂中-东段、甘孜—玉树断裂中-东段、龙日坝断裂南段、鲜水河断裂北西段和龙门山断裂南段库仑应力的减小.达日地震的发生导致后续1955年康定7.5级地震、1963年阿兰湖7.0级地震和2008年汶川8.0级地震等强震震源处累积(同震+震后)库仑应力变化分别为3.58×10^(3) Pa、1.16×10^(4) Pa、7.68×10^(3) Pa.结合震间构造应力累积速率的结果,认为1955年康定、1963年阿兰湖和2008年汶川地震的发震时间分别提前了约13.4年、40.6年和49.5年.上述结果显示块体内部强震对相邻边界断裂带上应力演化的影响不可忽略.

The 1947 Dari M 7.7 earthquake occurred inside the Bayan Har block.The effect of this earthquake on the stress evolution of the block boundary fault zone has been mostly ignored in the previous studies.In this study,we construct a three-dimensional viscoelastic finite element model of the eastern Bayan Har block and its adjacent areas,and analyze the Coulomb stress change caused by the Dari earthquake on the block boundary faults,considering the co-seismic dislocation and post-seismic viscoelastic relaxation effects.The results show that the Dari earthquake not only causes the significant increase of Coulomb stress change(>1.0×10^(6) Pa)in the adjacent non-ruptured sections on both ends of the Dari fault but also causes the co-seismic Coulomb stress increases on the middle-north section of the Longriba fault,the middle western section of the East Kunlun fault,the middle-south section of the Longmen Shan fault,the Barkam fault,the middle-south section of the Xianshuihe fault,and the western section of the Garzê-Yushu fault,with the maximum reaches 1.4×10^(4) Pa.On the contrary,the co-seismic Coulomb stress decreases on the middle-east section of the East Kunlun fault,the middle-east section of the Garzê-Yushu fault,the southern section of the Longriba fault,the northwest section of the Xianshuihe fault,and the southern section of the Longmen Shan fault.Moreover,the combined(co-and post-seismic)Coulomb stress change induced by the Dari earthquake on hypocenters of the 1955 Kangding M 7.5 earthquake,the 1963 Alan Lake M 7.0 earthquake,and the 2008 Wenchuan M 8.0 earthquake are 3.58×10^(3) Pa、1.16×10^(4) Pa and 7.68×10^(3) Pa,respectively.By integrating the accumulation rate of inter-seismic tectonic stress,we conclude that the 1955 Kangding earthquake,the 1963 Alan earthquake,and the 2008 Wenchuan earthquake are advanced by about 13.4、40.6 and 49.5 years,respectively.Our findings indicate the importance of strong earthquakes inside the block on the stress evolution on adjacent boundary fault zones.