近垂直共轭断层在地震中的动态激活:来自2023年土耳其Mw 7.6地震的启示  

Dynamic activation of near-orthogonal conjugate faults during earthquakes:Insights from the 2023 Türkiye Mw 7.6 earthquake

作　　者：丁啸天 谢军 徐世庆 Xiaotian Ding;Jun Xie;Shiqing Xu(Department of Earth and Space Sciences,Southern University of Science and Technology,Shenzhen 518055,China)

机构地区：[1]南方科技大学地球与空间科学系,深圳518055

出　　处：《科学通报》2024年第11期1501-1516,共16页Chinese Science Bulletin

基　　金：国家重点研发计划(2021YFC3000700);国家自然科学基金(42074048);广东省“珠江人才计划”(2021QN02G106)资助。

摘　　要：地表破裂迹线、有限断层反演和余震分布均表明,2023年土耳其Mw 7.6地震具有复杂的多段破裂特征,尤其在西侧存在一对在同震中被激活的近垂直共轭断层.根据经典断层力学理论,在均匀应力、脆性变形和小应变条件下,很难同时激活两个近垂直共轭断层.为了调查该现象,我们通过数值模拟二维情形下断层上的地震破裂过程和断层外介质的弹-塑性变形,来研究近垂直共轭断层在地震中的激活情况.模拟结果表明:(1)近垂直共轭断层在地震中并非同时被激活,而是在应力传递的作用下依次发生破裂,即二者间存在因果触发关系;(2)在一定夹角范围内,共轭断层均可能在地震中被动态激活,但具体的激活程度依赖于断层的几何构型和摩擦性质;(3)当前一个断层在交界处存在障碍体而非保持连续均匀时,与之成近垂直关系的后一个断层更容易被触发.这些结果从动力学角度为理解2023年土耳其Mw 7.6地震的主震破裂过程和余震分布提供了参考.由于在许多观测实例中(包括本次土耳其地震)后一断层的触发都发生在前一断层的拉张象限,我们推测正应力的动态释放在其中扮演了关键角色并且断层上的有效摩擦系数不能太低,从而不再需要援引高孔隙水压、低断层摩擦系数或者韧性变形等机制.Conjugate faults represent one or several pairs of faults,which are located close to one another but exhibit opposite senses of slip.The geometric configuration of conjugate faults,such as their intersection angle,depends on stress conditions and rock rheological properties,and may even change during the course of fault evolution.Classical fault-mechanics theory,such as the Anderson’s theory of faulting or the Mohr-Coulomb failure criterion,predicts that conjugate faults should form or become reactivated at~60°under dry,brittle(with typical friction coefficient of 0.6)and small-strain conditions,which has been widely verified by many field and experimental observations.However,in the last decades an increasing number of natural observations have shown that near-orthogonal conjugate faults can be activated during earthquakes,which is in stark contrast with the prediction of the classical fault-mechanics theory.Although several special mechanisms,such as high pore fluid pressure,low intrinsic rock friction and ductile deformation,are later proposed to explain the nearorthogonal configuration of conjugate faults,these mechanisms still do not provide a satisfactory explanation for the detailed process of fault activation during earthquakes.The 2023 Türkiye Mw 7.6 earthquake,which ruptured multiple fault segments including a pair of high-angle(~75°)conjugate ones to the west,provides a good opportunity to probe the activation process of near-orthogonal conjugate faults during earthquakes.Based on the available information from surface rupture trace,finite source inversion for the mainshock and relocated aftershocks,we build a simplified two-dimensional reference fault model,taking into account the diverse orientation of different segments and the connectivity condition between them.First,we use this reference model to numerically simulate a scenario of rupture process that is largely consistent with observations,including supershear rupture and depleted off-fault inelastic deformation along the western half of th

关 键 词：土耳其地震 共轭断层 断层再活化 地震破裂 应力传递 

分 类 号：P315[天文地球—地震学]