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Title:: Distribution and Significance of Crustal Thickness and Poisson's Ratio in Northwestern Yunnan

Author(s):: ZHANG Tianji; JIN Mingpei; LIU Zifeng; CHENG Yuhao; (Yunnan Earthquake Agency,Kunming 650224,Yunnan,China)

Keywords:: northwestern Yunnan; seismic meta-instability; receiver function; crustal thickness; Poisson's ratio

摘要:: 利用滇西北地震亚失稳观测实验区43个密集观测台站记录的2018年4月5日—12月30日远震三分量波形数据,计算并分析滇西北地区的地壳厚度和泊松比变化情况。结果表明:①研究区的地壳厚度总体呈现北深南浅的变化特征,且形成以云龙、蝴蝶泉—阳和、岩曲—羊窝棚—哨横为中心的3个莫霍面隆起区,在26°N附近形成一个向南的舌状突出,呈现两隆两凹状的莫霍面结构; ②研究区泊松比为0.209～0.328,整体被2条对角线分隔呈四象限分布,北、南两区是高泊松比(σ>0.28)地区,推测地壳物质富含铁镁质成分,西、东区为低泊松比(σ<0.26)区域,地壳物质可能富集长英质成分; ③云龙、蝴蝶泉—阳和以及南涧—红土坡地区的高泊松比(σ>0.3)可能是上地幔物质底侵致使下地壳物质部分熔融引起; 维西—乔后—巍山断裂北段的通甸—建基村,其与龙蟠—乔后断裂交汇的丰乐—禾头,以及维西—乔后—巍山断裂中段的脉地—紫阳村—瓦窑—太邑—岔河,是泊松比高梯度带,具备发生中强以上地震的孕震环境。

Abstract:: Using teleseismic waveform data recorded by 43 stations in meta-instability observation experiment area of northwestern Yunnan from April 5 to December 30,2018,we calculated and analyzed the changes of crustal thickness and Poisson's ratio in northwestern Yunnan.The results showed:the crustal thicknesses in this area are generally the variation characteristics of deeper in north and shallower in south; the three areas of Yunlong,Hudiequan-Yanghe,and Yanqu-Yangwopeng-Shaoheng are mantle uplifting sites,and the Moho surface is characterized as a tongue shape protruding southward and basically featuring two uplifts and two depressions near 26°N.The Poisson's ratio ranges from 0.209 to 0.328 in the study area,which is divided into four quadrants by two diagonal lines,the north and south regions are high Poisson's ratios(σ>0.28),the crust maybe enriched with iron and magnesium; the west and east regions are low Poisson's ratios(σ<0.26),the crust maybe rich in felsic.Very high Poisson's ratios(σ>0.3)are found in Yunlong,Hudiequan-Yanghe,and Nanjian-Hongtupo areas maybe the partial melting of lower crustal material caused by the bottom intrusion of upper mantle material.The Tongdian-Jianji,Fengle-Hetou,and Maidi-Ziyangcun-Wayao-Taiyi-Chahe areas are high gradient zones of Poisson's ratio and are seismogenic environments with moderate to strong earthquakes.