断层破裂速度对地震动及其地震灾害影响的有限单元法模拟  

Finite element method simulations of the influences of fault rupture velocities on ground motions and seismic hazards

作　　者：王松 朱守彪 WANG Song;ZHU ShouBiao(National Institute of Nature Hazards,Ministry of Emergency Management of China,Beijing 100085,China)

机构地区：[1]应急管理部国家自然灾害防治研究院,北京100085

出　　处：《地球物理学报》2022年第2期686-697,共12页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(41874060,41574041);国家重点研发项目(2017YFC1500104);中央级科研院所基本科研业务专项(ZDJ2020-15)共同资助。

摘　　要：断层破裂传播速度通常会影响强地面运动加速度的空间分布及地震的灾害程度,但究竟是如何影响的,目前未见全面的定量分析.为此,本研究设断层破裂速度从小到大发生改变(从亚剪切波速度到超剪切破裂速度),同时利用有限元方法计算在不同破裂传播速度的情况下,破裂产生的地震动及强地面运动峰值加速度(PGA)的空间分布,计算时保持在所有情况下其断层上的最终位错相等,即所有不同破裂情况下产生的地震矩震级保持不变,都为M_(W)=7.0.计算结果显示:总体上,破裂传播的速度越快,PGA的幅值越大并且高值区分布的范围也越广,其地震灾害会越严重;超剪切破裂相对于亚剪切破裂会加剧地震灾害.但是,当破裂速度正好等于介质的剪切波速度时,断层面附近PGA峰值最大,断层附近的地震灾害最为严重.此外,研究中还发现,当破裂传播速度等于√2倍剪切波速度时(该速度称为Eshelby速度),不产生剪切马赫波;这与超剪切破裂产生剪切马赫波的普遍现象不一致;但此时PGA并没有大幅度减小,其震害也不会有显著改变.因此,本研究对于深入认识地震震源过程、地震动效应以及灾害评估有着重要的科学意义及实用价值.The propagation velocity of fault rupture usually affects the spatial distribution of strong ground motions and the degree of earthquake disasters.However,there is no comprehensive study on how the rupture speeds affect seismic hazards.To this end,this study changed the rupture speeds of the fault propagation from small value to large magnitude(i.e.,from subshear wave velocity to supershear rupture speed),and at the same time,the finite element method was used to calculate the rupture scenarios and the corresponding ground motions.The spatial distribution of the peak ground acceleration(PGA)is calculated with the final dislocations on the fault kept the same in all cases,that is,the moment magnitude of the earthquakes generated under different rupture conditions remains unchanged,which is M_(W)=7.0.The calculation results show that,in general,the faster the rupture propagation speed,the larger the PGA is,and also wider the distribution of high-value areas.Accordingly,the more serious the earthquake disaster will be.Overall,the seismic hazard will be graver for the supershear rupture earthquake than that of subshear rupture event.However,when the rupture speed is exactly equal to the shear wave speed of the medium,the peak value of PGA near the fault is the largest,and the earthquake disaster is the most serious.In addition,this study also found that when the rupture propagation speed is equal to √2 times of the shear wave speed,which is called Eshelby velocity,no Mach wave appears.This is inconsistent with the general phenomenon of supershear rupture that generates Mach fronts.Therefore,this research is of important scientific significances and practical values for in-depth understanding of earthquake source process,ground motion effects and seismic hazard assessment.

关 键 词：断层破裂速度变化 强地面运动加速度 超剪切破裂 Eshelby速度 有限单元法 

分 类 号：P315[天文地球—地震学]