21世纪以来青藏高原大震前重力变化  

Gravity variations preceding the large earthquakes in theQinghai-Tibet Plateau from 21st century

作　　者：祝意青[1] 张勇[2,3] 张国庆[1,2] 刘芳 赵云峰[1] Yiqing Zhu;Yong Zhang;Guoqing Zhang;Fang Liu;Yunfeng Zhao(Second Crust Monitoring and Application Center,China Earthquake Administration,Xi’an 710054,China;School of Geodesy and Geomatics,Wuhan University,Wuhan 430079,China;China Earthquake Administration,Beijing 100036,China)

机构地区：[1]中国地震局第二监测中心,西安710054 [2]武汉大学测绘学院,武汉430079 [3]中国地震局,北京100036

出　　处：《科学通报》2020年第7期622-632,共11页Chinese Science Bulletin

基　　金：国家重点研发计划(2018YFC1503305);国家自然科学基金(41904082,41874092,61627824)资助。

摘　　要：青藏高原自21世纪以来连续发生了多次大震:2001年昆仑山口西8.1级、2008年新疆于田7.3级和四川汶川8.0级、2010年青海玉树7.1级、2013年四川芦山7.0级地震、2014年新疆于田7.3级和2017年四川九寨沟7.0级大震.这些地震前,中国地震局在青藏高原开展过多期流动重力观测,并观测到震中附近可靠的重力随时间的变化.本研究综合利用地面绝对重力、相对重力资料,通过对多种重力观测资料的整体处理分析,研究了青藏高原区域重力场变化及其与大震发生的关系.结果表明:(1)大震易发生在与构造活动块体边界有关联的重力变化正、负异常区过渡的高梯度带上,重力变化等值线的拐弯部位,构造活动块体边界是物质变迁和构造变形差异运动强烈的地带,易产生剧烈重力变化,积累应力应变而孕育地震.(2)2001年昆仑山口西8.1级地震发生在重力变化高梯度带与东昆仑断裂带交汇附近,2008年汶川Ms8.0和2013年芦山Ms7.0地震发生在龙门山断裂带的重力变化高梯度带上,2008和2014年两次于田Ms7.3地震发生在与康西瓦断裂走向基本一致的重力变化高梯度带零值线及梯度带的拐弯部位,2010年玉树7.1级地震发生在重力变化高梯度带与甘孜-玉树断裂上,2017年九寨沟7.0级地震发生在具有显著重力变化的塔藏断裂和岷江断裂构造活动断裂带附近.(3)重力资料对青藏高原2001年以来发生的7次大震均有较好反映,地震前震中区及其附近观测到明显的区域性重力异常及重力变化高梯度带,可能是地震孕育过程中观测到的重力前兆信息.根据重力资料显示的异常变化,对2008年于田Ms7.3和汶川Ms8.0、2013年芦山Ms7.0、2014年于田Ms7.3和2017年九寨沟Ms7.0地震均进行了较准确的中期预测,尤其是震中位置的判定.Since the beginning of 21st century, there have been 7 large earthquakes in the Qinghai-Tibet Plateau: The Kunlun Mountain Pass Ms8.1 earthquake in 2001, the Wenchuan Ms8.0 earthquake and the Yutian Ms7.3 earthquake in 2008, the Yushu Ms7.1 earthquake in 2010, the Lushan Ms7.0 earthquake in 2013, the Yutian earthquake Ms7.3 in 2014, and the Jiuzhaigou Ms7.0 earthquake in 2017. Prior to these earthquakes, the China Earthquake Administration(CEA) had gathered mobile gravity observations over several periods near the epicenter region, obtaining reliable gravity change with time data. In this study, the relationship between gravity variation and these 7 large earthquakes was analyzed using the absolute and relative gravity observations. The results revealed that:(1) The gravity variation fields related to the occurrence of these earthquakes were in response to the movement and change of underground fluid distributed deep in the crust. An enhanced regional stress field leads to deep material migration and transformation, which results in large-scale regional gravity change.(2) Large earthquakes tend to occur in the high-gradient transition zones between positive and negative gravity anomaly regions associated with the boundary of tectonic active blocks. The inflection point of the gravity change isoline is the transition zone between increasing and decreasing material density. The difference in the motions of the increasing and decreasing material is intense, and shear stress easily occurs in the high-gradient zones of the gravity change isoline. This leads to rupture, which then induces earthquakes.(3) The 2001 Kunlun Mountain Pass Ms8.1 earthquake occurred near the intersection of the high gradient zone of gravity change and the East Kunlun fault zone on the northern boundary of the Bayan Hara Block;the Wenchuan Ms8.0 earthquake in 2008 and the Lushan Ms7.0 earthquake in2013 occurred in the high gradient zone of gravity variation along the Longmenshan fault zone on the eastern boundary of the Bayan Hara block;the 2

关 键 词：青藏高原 重力变化 构造活动 大震活动 中期前兆 

分 类 号：P315.726[天文地球—地震学]