交角约90°共轭断裂的现今形变及对构造应力场的指示意义——以2019年M_(W)≥6.4菲律宾地震序列为例  

PRESENT DEFORMATION OF~90°INTERSECTING CONJUGATE FAULTS AND MECHANICAL IMPLICATION TO REGIONAL TECTONICS:A CASE STUDY OF 2019 M_(W)≥6.4 PHILIPPINES EARTHQUAKE SEQUENCE

作　　者：王雨晴 冯万鹏 张培震 WANG Yu-qing;FENG Wan-peng;ZHANG Pei-zhen(Guangdong Provincial Key Laboratory of Geodynamics and Geohazards,School of Earth Sciences and Engineering,Sun Yat-sen University,Zhuhai 519082,China;Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai),Zhuhai 519082,China)

机构地区：[1]中山大学地球科学与工程学院,广东省地球动力作用与地质灾害重点实验室,珠海519082 [2]南方海洋科学与工程广东省实验室(珠海),珠海519082

出　　处：《地震地质》2022年第2期313-332,共20页Seismology and Geology

基　　金：广东省引进人才创新创业团队(环南海地质过程与灾害创新团队)(2016ZT06N331);南方海洋科学与工程广东省实验室(珠海)创新团队建设项目(311021002);广东省基础与应用基础研究基金(2019B1515120019)共同资助。

摘　　要：共轭断裂是恢复区域构造应力场方位的主要地质学证据之一,其交角大小可能反映了当地的力学环境。交角约90°的情况是其中重要的一类,但目前对其认知仍较为有限。为研究此类断层的构造指示意义,文中以2019年10—12月菲律宾4次M_(W)≥6.4地震序列为例,采用InSAR空间测量学方法,精细研究了该过程的地表形变特征,进而确定了该地震断层系统的几何参数。结果显示,这4次地震发生在走向为48.8°、倾角为74.5°的右旋走滑断裂与走向为318.2°、倾角为68.9°的左旋走滑断裂上,可见2条断裂具有正交共轭的特征。经计算,2条断层主要滑动矢量间的最小旋转角达29.28°,在地震学意义上并不完全共轭。根据区域应力场结果,该共轭系统的剪裂角平分线方向与区域压应力的方位基本一致。余震分布显示发震断层延伸到莫霍面边缘,具备了成断层时潜在的韧性剪切条件。库仑应力模拟显示在共轭断裂系统中1支上的滑动过程可同时造成2支在交叉处一致的应力卸载作用,表明共轭系统中的2条断层对区域应力场卸载具有等效性。在全球范围内,搜集获取的共轭断层系统活动序列显示以“L”型展布的几何特征为主,且呈现2支断层发育不平衡的现象,该差异性很可能与断层之间的物性差异有关。Conjugate faults are a pair of faults developed under the identical regional tectonic stress fields with cross-cutting structures and opposite shear senses.They have been applied to restore the ancient regional tectonic stress fields,and the mechanics of local crust during its formation can be reflected by their dihedral angle.The~60°intersecting conjugate fault occurs under brittle environment as proposed by the Anderson theory,while the 110°intersecting conjugate fault could be formed under the conditions of ductile environment as explained by maximum effective moment(MEM)criterion.In addition,there is another kind of conjugate faults with~90°intersecting angle,which have been observed globally,but the mechanism of their formation still remains unsolved.Conjugate faults have been intensively studied using traditional geological methods and laboratory rock experiments.Interferometric synthetic aperture radar(InSAR),as an important geodetic mapping tool with an unprecedented precision and spatial resolution,provides a potential for investigating conjugate faults by exploring three-dimensional geometric structures.In this study,we investigated the 2019 M_(W)≥6.4 Philippines earthquake sequence as an example to link the present deformation characteristics of the ruptured conjugate faults to the regional tectonic stress.From October to December 2019,four M_(W)≥6.4 earthquakes occurred in Mindanao,Philippines.The epicenters were located in the Philippine Sea plate,at the junction of the Eurasian plate,the Pacific plate and the Indian Ocean plate.Affected by three-sided subduction,the plate boundaries are almost convergent boundaries with active tectonic movement and frequent seismic activities.The target earthquake sequence occurred in Mindanao where the Philippine Sea plate collided with the Sunda plate.According to the GCMT earthquake catalog,this earthquake sequence shows similar focal mechanisms to the eight M_(W)≥5.0 earthquakes in the study area before this earthquake sequence from 1992,which will have

关 键 词：正交共轭断裂 2019年菲律宾地震序列 InSAR同震形变 区域构造应力场 

分 类 号：P315.2[天文地球—地震学]