东昆仑断裂带中东段分段深部电性结构及其活动性研究

This work focuses on probing deep structure beneath the central-east section of the East Kunlun fault zone, i.e. the Maqing-Maqu section and its either side. It will use conventional and ultra-long-period magnetotelluric (MT) technologies to collect data and to image electric structure at depth by 2D inversion. Then, coupled with MT results on the Tosuohu and Tazang sections of the fault zone, 3D inversion of MT data will be conducted to image deep structure of the study area. Based on these MT and geological investigations, this work will analyze deep geometry and differential physical properties of the target area and their relation to crustal motion that is characterized by eastward decreasing rates along the fault zone. Furthermore, in combinations with data of heat flow, rock conductivity experiments at high-temperature and high-pressure, petrology and geochemistry, this study will compare features of electric structure, material composition and rheology of curst and upper mantle in surrounding areas including the Bayan Hara, Songpan-Ganzi, and Qaidam blocks and the West Qinling orogenic belt. Finally, in light of MT results of the Wenchuan, Lushan, Mingxian and Yushu earthquake areas, as well as geology and present-day 3D crustal motion on the eastern margin of the Tibetan plateau, this work will explore the deep context and source of driving force for major earthquakes along the rim of the Bayan Hara block.

采用常规和超长周期大地电磁测深技术，对东昆仑断裂带中东段的玛沁-玛曲段及其两侧地块的深部结构进行探测研究，反演获得二维深部电性结构图像；结合在托索湖段和塔藏段的大地电磁探测成果，开展区域三维电磁成像反演，获得该区三维深部电性结构图像。结合东昆仑断裂带中东段的地震地质调查成果，分析研究东昆仑断裂带中东段不同段落的的深部几何结构、介质物性差异及其与地表所观测的滑动速率自西向东明显减小的内在涵义，为深入研究东昆仑断裂带中东段地震活动性和孕震环境等研究提供深层次的证据。结合热流、高温高压岩石电导率实验、岩石学和地球化学等资料，研究巴颜喀拉和松潘-甘孜地块、柴达木盆地和西秦岭造山带地壳上地幔电性结构特征以及深部物质组成和流变特征。结合在汶川、芦山地震、岷县和玉树地震区的电磁成果，以及青藏高原东缘地质研究、现今三维地壳运动特征等成果，探讨巴颜喀拉地块周缘中强地震发生的深部构造背景和深部动力来源大地电磁

巴颜喀拉地块向北推挤受到昆仑—柴达木地块阻挡后沿东昆仑断裂带向东运动，而东昆仑断裂带的水平滑动速率自西向东表现为逐渐锐减的趋势，在向东延伸的同时将青藏高原内部动力转换到了青藏高原周边区域，是周边区域抬升的主要动力来源，近年来地震地质调查发现沿该断裂带的中东段还存在明显的“地震空区”。为了研究东昆仑断裂带中东段不同段落的深部结构分段性、几何结构、介质物性差异及其与强地震分布的关系，我们跨过东昆仑断裂带玛沁和玛曲段开展了常规和超长周期大地电磁探测，收集和整理了在托索湖段和塔藏段已有电磁探测成果，形成了跨过东昆仑断裂带中东段8个地段的8条大地电磁剖面数据以及发生东昆仑断裂带东端2017年九寨沟7.0级地震区密集电磁阵列电磁数据，采用了三维电磁成像技术对全部数据进行了反演。我们的结果揭示了东昆仑断裂带玛曲段以西断裂带延展状态呈现为略向西南倾斜的单一电性边界带，而在玛曲段以东则表现为以虎牙断裂向北延伸段为骨干电性差异带并伴随表现为电性差异带的塔藏、白龙江和光盖山-迭山断裂，四条断裂共同组成了一组西南向北东推挤的单侧“花状”结构样式，并统一归并于中下地壳HCL层中。大地电磁结果揭示东昆仑断裂带中东段不同地段具有不同高、低阻混杂的介质电阻率分布状态是东昆仑断裂带走滑速率向东锐减且成弥散分布的深部成因。2017年九寨沟7.0级地震震源区位于高、低阻交界区域，处于松潘-甘孜地块壳内低阻层（HCL）向北东方向涌动的端点附近，虎牙断裂向北延伸段在深部为明显的电性边界带，与北侧塔藏断裂组成单侧的“花状”结构归并于壳内低阻层中。松潘-甘孜地块北部中下地壳发育西南深-东北浅的低阻层（HCL），彰显出青藏高原向北东方向推挤，这是东昆仑断裂带尾端中强地震频发和地表隆起的动力来源。