摘要
四川盆地南部地区自2015年以来地震活动性持续增长,并相继发生了数次M5.0及以上的中强地震.2019年6月17日的长宁MS6.0地震则是其中震级最大的一次强震,且震后相继发生了一系列M5.0及以上的中强地震,给当地的生命和财产安全造成了极大危害.研究此次大震的地下结构和发震机制有助于理解该区地震异常活跃的机理,并为今后开展防震减灾工作提供参考.基于这个出发点,本文收集了长宁地震区的丰富地震走时资料,利用双差地震成像方法对长宁地震序列进行了重定位,并获得了研究区内的三维P波和S波速度及波速比结构.结果显示,长宁地震序列主要沿着白象岩—狮子滩背斜轴部展布.长宁地震区在6 km深度附近呈现出明显的低速、高波速比异常结构,指示着可能存在流体.研究区内的速度结构在6 km之上横向不均一性较强,速度异常结构整体呈NW-NWW向展布;而在7.5~12 km横向不均一性则较弱,速度异常结构整体呈NNE或SN向展布.这种速度结构特征可能指示着该区6 km之上基本为沉积层,而7.5 km之下则基本为结晶基底,上下存在解耦.研究区内绝大多数地震事件震级较小,且集中分布在6 km以浅,表明该区绝大多数事件受沉积层结构的控制.相较于白象岩—狮子滩和双河背斜区,长宁背斜在6 km之上呈现更为明显的高速结构,对应较强的力学性质,可能阻挡了本次长宁地震的东南向破裂而使其表现出明显的单向破裂特征.
The southern Sichuan Basin has a continuously increasing trend in seismic activity since 2015,among which are the numerous moderate and strong events with magnitude larger than 5.0.The Changning MS6.0 earthquake that occurred on 17 Jun.2019 is the largest one among these events and is followed by a series of moderate and strong aftershocks.The Changning earthquake sequence is extremely destructive and has led to a heavy loss on local life and property.The studies on the structure features and seismogenic mechanism of this large earthquake can help to understand the reasons why there is unprecedent intense seismic activity in this area,and provide important clues for future work on earthquake prevention and disaster reduction.Based on this point,we collected abundant seismic travel-time data and applied double-difference tomography method to relocate the Changning earthquake sequence and obtain high-resolution 3-D P and S wave velocity as well as VP/VS models.The results show that the Changning earthquake sequence is mainly distributed along the core of the Baixiangyan-Shizitan anticline.Significant low velocity and high VP/VS features are detected underlying the Changning earthquake source region around the depth of 6 km,suggesting the existence of fluid.Compared to the velocity structure between 7.5 and 12 km,strong heterogeneity is visible above 6 km in the study region.Besides,the overall anomalous velocity bodies are distributed along the NW-NWW direction above 6 km and NNE or SN direction between 7.5 and 12 km,suggesting the existence of a detachment layer there.The sedimentary layers are distributed mainly above 6 km,beneath which are the crystalline basement layers.Most seismic events are located above 6 km in depth with small magnitude,suggesting that the seismicity of the study region is mainly dominated by the structure of sedimentary layers.Significant higher velocity anomalies are observed underlying the Changning anticline above 6 km compared with the Baixiangyan-Shizitan and Shuanghe anticlines,which may obstruct the southeastward slip of the seismogenic fault of Changning MS6.0 earthquake,leading to the presence of striking unilateral source rupture.
作者
孙权
裴顺平
苏金蓉
刘雁冰
薛晓添
李佳蔚
李磊
左洪
SUN Quan;PEI ShunPing;SU JinRong;LIU YanBing;XUE XiaoTian;LI JiaWei;LI Lei;ZUO Hong(Key Laboratory of Continental Collision and Plateau Uplift,Institute of Tibetan Plateau Research,Chinese Academy of Sciences(CAS),Beijing 100101,China;University of Chinese Academy of Sciences,Beijing 100049,China;CAS Center for Excellence in Tibetan Plateau Earth Sciences,Chinese Academy of Sciences(CAS),Beijing 100101,China;Sichuan Earthquake Agency,Chengdu 610041,China)
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2021年第1期36-53,共18页
Chinese Journal of Geophysics
基金
国家自然科学基金(U2039203,41674090,41941016)
国家重点研发项目(2017YFC1500303)
中国科学院战略重点研究项目(XDA20070302)资助.
关键词
长宁MS6.0地震
双差地震成像
地震重定位
三维速度结构
Changning MS6.0 earthquake
Double-difference tomography
Hypocentral relocation
3-D seismic velocity structure
