【作者】 邵翠茹；

【导师】 尤惠川；

【作者基本信息】 中国地震局地球物理研究所 ， 地球探测与信息技术， 2009， 硕士

【摘要】 雅鲁藏布大峡谷位于喜马拉雅山脉东部,是印度板块向北与欧亚板块碰撞的喜马拉雅东构造结的核心部位,地壳结构复杂、构造运动强烈、地震活动频繁、自然灾害严重。然而,由于大峡谷地区环境恶劣、交通不便,致使其核心部分仍然是科学调查与研究的空白区,这里的地震监测能力低下,对地震活动性还没有进行过专门的分析和研究,是探索地震活动性与深浅构造关系的理想场所。作者综合有关地质调查、地震台阵建设、数据采集与数据处理、资料解释过程中发现的现象和遇到的问题,形成了论文的基本研究思路:通过历史破坏性地震资料、现代小震资料及大峡谷地区临时地震台阵监测获得的资料,进行地震定位和震源机制解等数据处理,结合深浅构造特征,对雅鲁藏布江大峡谷地区的地震活动规律和构造应力场特征进行分析,并初步探讨其与东喜马拉雅(南迦巴瓦)构造结的深浅构造关系。论文包括以下具体工作内容:地震台阵建设、运行和数据采集;地震数据处理(地壳速度模型建立、地震波形数据处理、地震定位、震源机制求解);地震活动性和构造应力场特征分析;地震活动与深浅构造的关系及孕震构造条件讨论。论文工作实现了从地质调查、台阵选点、台站建设、数据采集、数据处理、资料分析和结果讨论等环节技术初步的掌握。论文从地球物理应用角度出发,联系地质构造,较为系统地研究了地震活动性分析技术和研究方法,研究结果一定程度上阐明了雅鲁藏布大峡谷地区的地震活动性和构造应力场特征及其与深浅构造的关系,填补了该区相关研究的空白。论文研究理论紧密结合实际,得到了以下主要结果、结论和认识:①雅鲁藏布大峡谷地区地震活动强烈,历史上记载有M_s≥4.7级破坏性地震157次,其中6.0级及6.0级以上地震21次,最大地震为1950年察隅-墨脱8.6级地震。②临时地震台阵第一期(2007.8—2008.8)记录大峡谷地区203次地震,最小震级为0.6级,最大为4.6级,其中M_L≥1.8级地震资料基本是完整的。③地震活动与构造运动强度和分区及断裂构造关系密切,表现出明显的时空不均匀性,主要分布于大拐弯前锋(5—6级)、墨脱断裂带和阿帕龙断裂带(8.6级)、班公-怒江断裂带和嘉黎断裂带(6—7级)和东喜马拉雅内部等。④区内地震多属浅源地震,地震最大深度向北、向东变大,强震分布在深40—60km(从南向北加深、从南迦巴瓦构造结向东西两侧变浅)的界面之上。⑤地震分布特征反映了地壳块体的构造作用,显示其受到印度板块向北俯冲、南迦巴瓦构造结向北东楔入的摔制。⑥强烈地震主要发生在块体周边的深断裂带及其附近,7级及以上地震主要与北西向和北东向断裂构造带有关,尤其是与断裂构造带中规模较大、全新世强烈活动段密切相关。其中,8级地震主要发生存断裂构造带中走滑分量较大的北西西向断裂带上;而以倾滑为主、单条规模不大的断裂,最大震级为7级左右。⑦强烈地震还经常发生在断裂几何构造复杂部位或多组方向断裂交汇区。⑧7级以上大地震多发生在地壳厚度陡变带、布格重力异常梯级带上,6级以上强震大多发生在重力异常等值线同形扭曲、不同活动块体之间的不同重磁异常区的分区界线上。⑨雅鲁藏布大峡谷地区的构造应力场是以北东-北北东向近水平挤压为主的复杂图像,易于发生走滑、逆冲和走滑逆冲型的断层活动。更多还原

【Abstract】 Yarlung Tsangpo Grand Canyon is located in the eastern Himalayas,is the core parts of the eastern Himalayas structures,which is formed by Indian plate moved northward and collided with Eurasian plate,the crust structure is complex,the tectonic movements are intensive,the earthquakes are frequent,the natural disasters are serious.However,the Grand Canyon area as a result of environment and transport facilities,the core of it is scientific investigation and research gaps,where the capacity of the seismic monitoring is lower,seismic activity has not been specialized analyzed and researched,here is an ideal site to explore the seismic activity and the relationship between deep and shallow structures.The author integrated the phenomenon and problems which were discovered in the process of geological survey,seismic array construction,data acquisition,data processing and information explanation,formed a basic research idea of this paper: proceeding earthquake locations and focal mechanism solutions,by history devastating earthquakes information,modern small earthquakes information and the temporary seismic array data of the Grand Canyon region,combined with the characteristics of deep and shallow structures,to analyze the seismic active regularity and the characteristics of tectonic stress field of Yarlung Tsangpo Grand Canyon region,preliminary study the relationship between deep and shallow structures with Eastern Himalayas(Namjagbarwa)structure.The Paper includes the following specific contents:seismic array construction, operation and data acquisition;seismic data processing(crust velocity model building, seismic waveform data processing,earthquake locations,focal mechanism solutions); seismic activity and the characteristics of tectonic stress field analysis;the relationship between earthquake activities and the deep-shallow structures and discussing the conditions of the structure of earthquake preparation area.The paper realized the grasp of geological survey,sites choice,array building,data acquisition, data processing,data analysis and results discussion.The paper from the application point of view of geophysics,contacted with geological structure,studied the analytical techniques and research methods of seismic activity more systematic,the research results to some extent,explained the Yarlung Tsangpo Grand Canyon region seismic activity,the characteristics of tectonic stress field and the relationship between deep and shallow structures,filled the gaps in relevant research area. The papers research theory is close connected with reality,by the following major findings,conclusions and understanding of:①The seismic activity of Yarlung Tsangpo Grand Canyon is strong,there are 157 destructive earthquakes in history which M_s≥4.7,including 21 earthquakes which M_s≥6.0,the largest earthquake is Zay-Moto earthquake which M_s=8.6 and occurred in 1950.②Phase I of the temporary seismic array(2007.8-2008.8) recorded 203 earthquakes,the smallest magnitude is 0.6,the maximum magnitude is 4.6,the information of the earthquakes which M_L≥1.8 is complete.③Seismic activity is closely related to tectonic movement strength and divisional and fracture structure,time and space show that heterogeneity,is mainly distributed in the forward of the Grand Canyon region(5-6 magnitude),the Moto fault zone and Appalachian Long fault zone(8.6 magnitude),Bangong-Nujiang fault zone and Jiali fault zone(6-7 magnitude) and internal of the eastern Himalayas.④The earthquakes in the region are mostly shallow,maximum depth of the earthquake is in the north and the east,strong earthquakes are in the deep of 40-60km (deepened from south to north,turn shallow from Namjagbarwa structure to the east and west sides).⑤The distribution characteristics of earthquakes reflect the crust structure, show Indian plate northward subduction,Namjagbarwa structure northward and eastward subduction.⑥Strong earthquakes occur in the blocks surrounding where is the deep fault zone and its vicinity,and over seven magnitude earthquakes are related to the faults in north east direction and northwest direction,in particular closely related to the fault zones of the larger and strong activity of Holocene epoch.Of these,eight magnitude earthquakes occur in the faults in west northwest direction with strike-slip component larger;but mainly dip-slip,a single fracture no scale,the largest magnitude is about 7.⑦Strong earthquakes often occur in parts of the complex geometry or a convergence of directions of fracture zones.⑧Over seven magnitude earthquakes occur in the crust thickness changes with the steep,gradient zones of gravity anomaly belt,over seven magnitude earthquakes occur in the anomaly with the shape distortion between the different activities of the different pieces of gravity and magnetic anomalies district boundary. ⑨The tectonic stress field of Yarlung Tsangpo Grand Canyon region is ne-nne to nearly the level of extrusion,prone to strike-slip,thrust and strike-slip thrust faults.更多还原