滇西北地区主要断裂带及邻区三维P波速度结构的双差地震层析成像

doi:10.12196/j.issn.1000-3274.2021.03.004

摘要/Abstract

摘要： 利用区域固定台站和中国地震科学探测台阵记录的7349个近震事件的60471个Pg波绝对走时和196465个相对走时数据, 采用双差地震层析成像获得滇西北地区(25°~28.2°N, 99.5°~101.5°E)横向分辨率为0.2°的中、上地壳的三维P波速度模型, 重点分析了区域内各主要断裂带及其邻区的速度结构特征。结果表明: 金沙江—红河断裂带北段15 km以上的P波速度较低, 重定位后中、小地震的震中主要位于低速异常的内部, 且震源深度在断裂带两侧相似; 推测金沙江—红河断裂带作为川滇菱形块体西南边界的剪切控制作用已弱化, 分界能力局部减弱, 并且断裂带下方主体的低速异常可能为跨越断裂的动力传递提供条件。丽江—小金河断裂带(西南段)两侧存在大范围的P波低速异常, 推测此低速体可能是青藏高原东南向挤出的物质, 而程海断裂带以东从近地表至25 km深处明显的P波高速异常体则可能会阻挡高原物质东南向的逃逸。

关键词: 双差地震层析成像, 三维P波速度结构, 金沙江—红河断裂带, 丽江—小金河断裂带, 程海断裂带

Abstract: We determined a 3D P-wave velocity model of the middle and upper crust under the northwest Yunnan (25°~28.2°N, 99.5°~101.5°E) by using double-difference seismic tomography and jointly inverting 60471 absolute arrival times and 196465 differential arrival times from 7349 local events recorded by permanent seismic network and ChinArray. Our results show that a low P wave velocity zone is existed above 15 km in the northern section of the Jinshajiang-Red River fault zone, and majority of hypocenters are located in low velocity anomalies and focal depths are similar on both sides of the fault zone. We speculate that the role of the Jinshajiang-Red River fault zone as the southwest boundary of the Sichuan-Yunnan diamond block is weakening, and low velocity anomalies below the fault zone may helpful to dynamic transmission across the fault zone. There are large range of low velocity anomalies on both sides of the southwest section of the Lijiang-Xiaojinhe fault zone, and we deem that these low velocity anomalies may be the Tibetan plateau material which have been extruded. On the east of Chenghai fault zone, there are obviously P wave high velocity anomalies from near surface to 25 km depth, and these high velocity anomalies may block the southeastern escape of the plateau material.

Key words: Double-difference seismic tomography, 3D P-wave velocity structure, Jinshajiang-Red River fault zone, Lijiang-Xiaojinhe fault zone, Chenghai fault zone

中图分类号:

P315.7

杨峰. 滇西北地区主要断裂带及邻区三维P波速度结构的双差地震层析成像[J]. 地震, 2021, 41(3): 42-58.

YANG Feng. Double-difference Seismic Tomography of the 3D P-wave Velocity Structure of Major Fault Zones and Adjacent Areas in Northwest Yunnan[J]. EARTHQUAKE, 2021, 41(3): 42-58.

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