非均匀断层上的破裂传播及对震级预测的挑战  

Rupture propagation on heterogeneous fault:Challenges for predicting earthquake magnitude

作　　者：杨宏峰[1,2] 姚素丽 陈翔 Hongfeng Yang;Suli Yao;Xiang Chen(Earth System Science Programme,the Chinese University of Hong Kong,Hong Kong,China;Shenzhen Research Institute,the Chinese University of Hong Kong,Shenzhen 518057,China)

机构地区：[1]香港中文大学地球系统科学系,中国香港 [2]香港中文大学深圳研究院,深圳518057

出　　处：《科学通报》2022年第13期1390-1403,共14页Chinese Science Bulletin

基　　金：国家重点研发计划(2018YFC1503400);中国地震科学实验场项目(2018CSES0102);香港研究资助局优配研究金(14306119,14306418);地震数值预测联合实验室开放基金(2021LNEF02)资助。

摘　　要：针对发震断层上的潜在地震开展震级和地表震动预测,对开展地震灾害区划、防震减灾等工作十分关键.由于断裂带本身的多种非均匀性,如断层几何、介质结构、应力的非均匀分布,准确预测震级面临着众多挑战.本文简要回顾了影响地震破裂传播及震级的因素,指出了应力分布状态、断层孕震带尺度、断裂带介质结构对破裂传播过程的影响.在非均匀应力分布下,震级对破裂起始位置(震中)具有强烈的依赖性,即震中-震级存在“测不准”关系,震中对破裂是否延伸到地表也有控制作用.走滑断裂带孕震带尺度(在倾向上的深度)对破裂是否发展为“逃逸型”大地震有控制作用.近断裂带的介质结构对破裂方向性、延展尺度都有显著影响.未来可通过密集地震台阵观测获取高分辨率断裂带结构,并结合实验室流变性质测量,推断发震断层的流变结构,为刻画可能发震的凹凸体提供支撑.针对震中对震级的影响,可以通过破裂动力学模拟,结合大地测量观测、地震学观测、实验室摩擦实验结果,进行数值实验,探索可能发生强震的震中区域,为野外观测提供参照.此外,动力学数值模拟结果也可以弥补大地震近场地表震动观测数据缺乏的不足,为开展基于地震物理过程的灾害区划提供参考.Predicting magnitudes and ground motion of future strong earthquakes on seismogenic faults holds critical implications on seismic hazard zonation and mitigation.Although present approaches to seismic hazard assessment can effectively identify potential regions to host strong earthquakes,it remains extremely challenging to accurately predict future earthquake magnitudes because of various heterogeneities of fault zones,such as fault geometry,medium structure,and frictional properties.In this work,we review a few aspects that play important roles in earthquake rupture propagation and extent,so as to determine the final magnitude of earthquakes.Under the condition of heterogeneous stress distribution on faults,the final magnitude of earthquakes as well as shallow slip distribution depends on where the rupture initiates.As shown in recent numerical models of dynamic rupture simulations,different hypocenters with similar stress level can lead to completely different rupture scenarios,some of which may significantly break the ground whereas others may be buried underground.Such findings shed critical light on seismic hazard preparation,because surface-breaching ruptures can lead to severe damage as vividly evidenced by the 2022 Menyuan Mw6.7 earthquake.To date,we cannot predict future hypocenter locations according to our knowledge of earthquake nucleation and therefore future relevant investigations are highly demanded.Furthermore,the size of seismogenic zone on strike-slip faults controls whether ruptures may become“break-away”to form large earthquakes or stop spontaneously as“self-arresting”of moderate magnitude events.Observations show that aspect ratios between rupture length and down-dip width of dip-slip earthquakes are usually no more than 8.In contrast,the length/width ratios of strike-slip earthquakes may rise to 40 and have a drastic change around the rupture width of~10 km.Intrinsic mechanism of such variation in strike-slip earthquakes is attributed to the energy release rate of rupture fronts,whic

关 键 词：地震预测 断层非均匀性 地震破裂传播 震中依赖性 地震动力学数值模拟 

分 类 号：P315.7[天文地球—地震学]