摘要
2015年尼泊尔Ms8.1地震的余震分布、震源机制解、震源破裂过程反演结果和喜马拉雅造山带地质构造特点表明,此次大震是印度板块沿喜马拉雅主前缘逆冲断裂向欧亚板块进行低角度俯冲的结果。地震破裂从北西向东南方向传播,累计长度达170km,最大倾向滑移量5-7m。其发震断裂全新世活动强烈,历史地震活动频率高、强度大,M≥7.5地震的原地复发平均间隔在500年左右,而在地震活跃阶段分段破裂的平均间隔只有10年左右,并且历史地震活动在最近1800年期间显示出比较明显的从西向东迁移规律。历史地震活动过程揭示,喜马拉雅主逆冲断裂带上目前存在兴都库什、尼泊尔西部、锡金-不丹和印缅交界区4个地震空区段,特别是位于此次地震东部的两个空区,未来地震危险性较显著。由于印-欧大陆俯冲碰撞作用是中国大陆现今地壳变形的主要动力来源,也是中国大陆强震频发的主要地质构造原因,这决定了喜马拉雅、青藏高原及邻区的大震活动之间存在明显的时空关联性,主要表现为大地震活跃阶段在时间上的交替出现和大地震沿垂直喜马拉雅造山带的纵向迁移过程。进一步结合青藏高原及邻区历史地震活动及未来地震危险性的分析成果推断,在喜马拉雅地震带的新一轮活跃过程中,中国大陆必将面临更为严峻的地震形势,尤其是青藏高原及邻区晚第四纪活动性显著的区域性活动构造带或断裂带的潜在强震危险性比较突出,主要包括:藏南的近南北向裂谷带与北西向右旋走滑断裂带,川滇地块中的安宁河-小江断裂带与大凉山断裂带、南汀河断裂带与畹町断裂带、澜沧-景洪断裂带和滇西北大理-丽江裂陷带,西北地区的西昆仑山前逆冲-褶皱带、阿尔金断裂带和天山的主要逆冲-褶皱变形带等。但当前活动构造调查研究的不足限制了对区域大地震危险性做出更准确的地质评估,这也是目前城镇化与重大工程规划建设过程中地壳稳定性评价的"瓶颈"所在。
Aftershock distribution,focal mechanism interpretation,inversion result of source rupture process of the 2015 Ms8.1Nepal great earthquake and Cenozoic tectonic of the Himalayan orogenic belt shows that the Ms8.1great earthquake resulted from low-angle subduction of Indian plate towards the Eurasian plate along the Main Himalayan Thrust(MHT)fault zone.The focal rupture propagated from northwest to southeast along the MHT trend,with an accumulated length of about 170 km and a maximum dip-slip displacement of about 5-7 m.The focal rupture was active at most during the Holocene,with high frequencies and high magnitudes.Along the MHT,earthquakes with Ms ≥7.5occurred very 500 years and the average interval of earthquake segmentation rupture was only 10 years or so during active phase of earthquakes.Historical records show that seismic activities migrated distinctly from west to east along the MHT during last 1800 years,revealing that four seismic gaps,including the Hindukush,western Nepal.,Sikkim-Bhutan and India-Myanmar border area from west to east respectively along the MHT,occur in the Himalayan thrust belt,especially the last two gaps to the east of the 2015 Nepal earthquake vulnerable to geohazards.Collision between Indian plate and Eurasian plate is not only the driving force for deformation of present Chinese continent but the leading tectonic factor for frequent occurrence of strong earthquakes in China.Our study shows there is spatial-temporal relation of big seismic activities in Himalayas,QinghaiTibet plateau and adjacent areas,which are reflected by alternative occurrences of big earthquakes during active stages and vertical migration of big earthquakes perpendicular to the Himalayan orogenic belt.The previous seismic records in the Qinghai-Tibet plateau and adjacent areas and analysis results of future seismic geohazards reveal that during a next new round of seismic activity in the Himalayan seismic belt,Chinese mainland will likely face the sever situation of seismic hazard,especially the regional active tectonic belt or faulting belt of the Qinghai-Tibet plateau and adjacent areas at the late Quaternary will have a high risk for strong earthquakes.The areas includes:nearly N-S trending rift zone and northwest right-lateral strike-slip fault zone in southern Tibet,Anning river-Xiaojiang fault zone,Daliangshan fault zone,Natinghe fault zone,Wanding fault zone,Lancang-Jinghong fault zone and Dali-Lijiang graben belt of northwest Yunnan in Sichuan-Yunnan block,West Kunlun thrust-fold belt,Altyn Tagh fault zone,and main thrust-fold structure belts around Tianshan mountain in the northwestern region of China etc.But less investigation for and study of active tectonics in southwest China has not only restricted much precise geological assessment for geohazards triggered by strong regional earthquakes but been the bottleneck for evaluation of crust stability to national planning and construction for urbanization and key engineering projects.
出处
《地质学报》
EI
CAS
CSCD
北大核心
2016年第6期1062-1085,共24页
Acta Geologica Sinica
基金
国家自然科学基金项目(批准号:41171009)
中国地质调查局项目(1212011120163
12120114002101)
中国地质科学院地质力学研究所基本科研业务费项目(DXLXJK201410)共同资助的成果