摘要
近10年以来,在四川盆地南部的川黔滇交界地区发生了一系列中、强地震,其发震机理引起了广泛的关注和讨论。本文基于历史地震震中分布和区域活动断裂构造编图,发现四川盆地南部地震主要集中在4个地震亚区,分别为马边—永善、鲁甸、长宁和自贡—荣昌等地震亚区,华蓥山断裂带西南段是其中一条重要的地震构造边界带。通过综合分析主、余震分布特征、震源深度和震源机制解等资料,认为该地震区存在2类发震断层,其中马边—永善、鲁甸、长宁地震亚区以基底断层走滑型或走滑逆冲型地震为主,而自贡—荣昌亚区则以浅层滑脱断层逆冲型地震为主。区域挤压应力方向从WNW-ESE向至ENE-WSW向。双震型地震频发,一次走滑地震往往会触发一组共轭基底断层的同时活动。这些地震构造特征表明它们不同于盆地西缘的龙门山—岷山逆冲走滑型地震构造带,也不同于鲜水河—安宁河—小江走滑型地震构造带,属于一个新生的克拉通地震构造区,因西南扬子地块遭受青藏高原的向东推挤和压迫,构造应力通过"大凉山地块"传递并作用到四川盆地南部,导致扬子地块的断块型结构及其基底断层的逆冲走滑活动,进而主导了该地区的一系列中、强地震的破裂事件。
A series of large-to-moderate earthquakes shocked,during the last decade,the southern region of the Sichuan basin in the conjunction area of Sichuan,Yunnan and Guizhou Provinces,which has provoked a vivid discussion on their seismogenic regime and seismic risk assessments in a cratonic block setting.In this study,we compiled regional active faults and historic earthquake epicenters and delineated four seismic sub zones,namely the Mabian-Yongshan,Ludian,Changning,and Zigong-Rongchang ones.An integration of seismotectonic data such as main shock-after shock distribution pattern,focal mechanisms and focal depth,shows that there exist two kinds of seismogenic structures:the basement strike-slip or reverse strike-slip faulting that dominated the seismic activity in the Mabian-Yongshan,Ludian and Changning sub-zones,and shallow reverse faulting that prevailed in the Zigong-Rongchang sub-zone.The maximum horizontal stress axe(compressional)orient from WSW-ENE to WNW-ESE.Double-earthquakes occurred frequently,with one shock event often triggering a conjugate strike-slip fault.These characteristics imply that the seismogenic structures of this seismic zone differ either from the reverse dominated faulting along the Longmen Shan seismic zone of the western Sichuan basin,or from the reverse to strike-slip-dominated faulting along the Xianshuihe-Anninghe-Xiaojiang seismic zone.It is considered that this is a neo-forming seismic zone in the interior of the Yangtze cratonic block.Tectonic stresses generated by eastward push of the Tibetan Plateau are transferring,via"Daliang Shan block",to the south Sichuan basin,which activated the preexisting faults in the cratonic basement,and subsequently led to strike-slip to reverse strike-slip faulting earthquake sequences.
作者
张岳桥
ZHANG Yueqiao(School of Earth Sciences and Engineering,Nanjing University,Nanjing,210023)
出处
《地质学报》
EI
CAS
CSCD
北大核心
2020年第11期3161-3177,共17页
Acta Geologica Sinica
基金
国家自然科学基金项目(编号41472178)资助成果。
关键词
四川盆地南部地震区
地震分区特征
基底走滑型和走滑逆冲型地震
浅层逆冲型地震
构造应力场
south Sichuan basin seismic zone
seismic zonation
basement strike-slip to reverse faulting earthquake
shallow reverse faulting earthquake
tectonic stress field
