利用远震P波接收函数研究漾濞M_(S)6.4地震孕震环境  

The study of seismogenic environment in Yangbi M_(S)6.4 earthquake region by teleseismic P-wave receiver function

作　　者：张天继 金明培[1] ZHANG TianJi;JIN MingPei(Yunnan Earthquake Agency,Kunming 650224,China)

机构地区：[1]云南省地震局,昆明650224

出　　处：《地球物理学报》2021年第12期4462-4474,共13页Chinese Journal of Geophysics

基　　金：云南省地震局青年地震科学基金(2019K02);国家重点研发计划(2018YFC150330303);国家自然科学基金(41874111)资助.

摘　　要：2021年5月21日我国云南省大理州漾濞县发生了M_(S)6.4级破坏性地震,该地震的深部孕震环境研究对理解其成因极为重要.本文利用滇西北地区68个密集地震台站记录的远震波形数据,提取P波接收函数,采用两步反演法和Bootstrap重采样统计技术,获取了滇西北地区精细的地壳上地幔80 km深度范围内的S波速度结构.结合前期所得地壳厚度与泊松比分布情况分析认为:滇西北地区地壳S波速度结构在横向上和垂向上都具有强烈的非均匀性,浅表约有4 km厚的低速沉积层,中上地壳呈高低速相间分布特征;20~40 km深度范围内存在低速层,分布在维西—乔后—巍山断裂与红河断裂两侧.从横向上看,漾濞地震发生在维西—乔后—巍山断裂西侧的高低速过渡地区和泊松比高梯度带上.从垂直剖面上看,漾濞地震发生在中下地壳具有明显低速层、而上覆为相对高速的脆性地壳中,震源区地壳内存在的低速体为此次漾濞地震提供了可能的孕震环境.滇西北地区的中下地壳低速层被断层限制在特定的区域内,且该地区存在莫霍面隆起中心、非常高的泊松比值(>0.3)以及上地幔低速异常,考虑到高热流、地幔高导层隆起、温泉幔源特征等综合分析推测低速体可能与地幔热物质上涌有关.On 21st May 2021,a destructive M_(S)6.4 earthquake occurred in the Yangbi County,Dali Prefecture,Yunnan Province,China.The study on tectonic environment of the earthquake is crucial for understanding its genesis.From teleseismic waveform data recorded by dense stations in Northwestern Yunnan,we isolated P-wave receiver functions with high signal-to-noise ratio and investigated the S-wave velocity structure of the crust and upper mantle within the depth range of 80 km in Northwestern Yunnan via applying tow-step inversion procedure and the Bootstrap technique.Considering the distribution of crustal thickness and Poisson′s ratio in Northwestern Yunnan obtained previously,we deduced that the crustal S-wave velocity structure in Northwestern Yunnan is strongly inhomogeneous both horizontally and vertically;there are low-velocity sediments from the surface to about 4 km;the velocity structure is characterized by alternating high and low anomalies in the middle-upper crust;the low-velocity layers in depth of 20~40 km occur on the both sides of the Weixi-Qiaohou-Weishan fault and Red River fault.From the cross section,the Yangbi M_(S)6.4 earthquake happened in the transition zone of low-high velocities and the high Poisson′s ratio gradient zone on the west side of Weixi-Qiaohou-Weishan fault.According to the vertical profile,the Yangbi M_(S)6.4 earthquake took place in the brittle crust with a relatively high velocity above the middle-lower crust where there is an obviously low-velocity layer.The low-velocity layer under the epicenter may induce the seismogenic environment.In Northwestern Yunnan,the low velocity in the middle-lower crust appears to be limited in a specific area by the faults,and there exist Moho uplifts,extremely high Poisson′s ratio(>0.3)zones and low-velocity anomalies of upper mantle.Combing with the high value of geothermal flow,uplift of highly conductive layer in the mantle and the mantle source characteristic of hot spring in this region,we inferred the low velocity is related to the upwell

关 键 词：漾濞M_(S)6.4地震 S波速度结构 两步反演法 中下地壳低速层 泊松比高梯度带 孕震环境 

分 类 号：P315[天文地球—地震学]