鄂尔多斯活动地块边界带第四纪晚期构造活动特征及强震孕育机制

Late Quaternary tectonic activity and strong earthquake generation mechanism around the boundary zone of the Ordos active-tectonic block,central China

鄂尔多斯地块是位于中国内地中心位置的典型活动地块,由于受西南部青藏地块和东部太平洋板块远程作用的影响,地块各边界带构造活动特征和变形具有明显的特殊性和差异性。文章总结了多年来围绕鄂尔多斯活动地块周缘边界带开展的活动断裂定量、地震孕育机制及活动特征等的已有研究结果,对地块周缘断裂活动特征及强震孕育机制进行系统总结。鄂尔多斯活动地块不同边界带断裂第四纪晚期活动特征的不同是强震孕育环境差异的最直接的证据。鄂尔多斯活动地块西边界构造变形样式复杂,受青藏高原向北东挤压扩展的影响,西边界南段断裂以走滑、逆走滑和逆冲为主要特征。而向北到西边界北段,以右旋走滑为主要特征;以青藏高原最新扩展前缘的三关口-牛首山断裂为界,北部的银川盆地表现为典型的断陷盆地,边界断裂有右旋走滑特征,地震活动多以正走滑型为主。北边界的河套盆地以北侧的正断层为其控盆构造,历史和古地震多集中在北侧边界断裂上。南边界的渭河盆地构造特征相对较为复杂,由两组正断层组成,历史大地震多发生在盆地南缘,盆地中北部有中强地震发生。东边界的山西地堑系由多个裂谷型盆地斜列组成,历史大地震表现为南强北弱,北部盆地受张-渤构造带的影响,盆地走向和断层运动性质均发生了明显变化,多具备发生7级左右地震的构造条件。综合认为,断裂活动特征典型的鄂尔多斯活动地块周缘各边界带,未来强震多发生在大地震离逝时间长的地震空区/空段,或是构造带的转换和交汇区。

[Objective]The Ordos block,with typical boundary zone activity,is located in the center of China's Mainland.Influenced by the remote action of the Tibetan Plateau in the southwest and the Pacific Plate in the east,each boundary zone of the Ordos Block exhibits distinct tectonic activity and deformation characteristics.This study aims to provide insights into the characteristics of strong earthquake generation and the future seismic risk along the boundaries of the Ordos active block.[Methods]This study systematically summarizes research achievements made in the study of active faults and the seismogenic mechanism of strong earthquakes around the Ordos Block over the past few decades,providing a systematic overview of the characteristics of fault activity and seismic generation mechanisms along the block’s periphery.[Conslusion]The differences in fault activity in each boundary zone determined the differences in the earthquake-breeding strong tectonic environments.In the southern section of the western boundary,the faults are mainly characterized by strike-slip,reverse strike-slip,and thrust owing to the influence of the northward compression and expansion of the Qinghai-Tibet Plateau,resulting in complex structural deformation styles within the boundary zone.In the northern section of the western boundary,the latest expansion boundary of the Qinghai-Tibet Plateau is characterized by dextral movement along the Sanguankou-Niushoushan fault.The Yinchuan Basin in the northern section of the western boundary zone is a typical fault basin with basin-controlling faults exhibiting dextral strike-slip characteristics,and earthquakes are primarily of the standard strike-slip type.The Hetao Basin on the northern boundary is controlled by normal faults on its northern side,with historical and ancient earthquakes concentrated on the northern boundary faults.The Weihe Basin on the southern boundary exhibits relatively complex structural features,comprising two sets of normal faults.Historical major earthquakes mostly occur at the southern edge of the basin,with moderate seismic activity in the central-northern part of the basin.The Shanxi Graben system on the eastern boundary comprises multiple rift-type basins.Historical major earthquakes exhibit a pattern of stronger activity in the south and weaker activity in the north.The northern basins are influenced by the Zhang-Bo tectonic belt,resulting in significant changes in basin trend and fault movement characteristics,often possessing the structural conditions necessary for earthquakes of around M 7.0.Overall,in the typical fault activity zones surrounding the Ordos active block,future strong earthquakes are more likely to occur in seismic gaps or transition zones of fault systems,where significant time has passed since the occurrence of major earthquakes or at the intersections of tectonic zones.