青藏高原东缘扶边河断裂周边地壳密度及垂向构造应力特征  

THE CRUSTAL DENSITY STRUCTURES AND ISOSTATIC ADDITIONAL STRESS AROUND THE FUBIANHE FAULT ON THE EASTERN MARGIN OF TIBET PLATEAU

作　　者：张国庆 祝意青[1] 梁伟锋[1] ZHANG Guo-qing;ZHU Yi-qing;LIANG Wei-feng(The Second Monitoring and Application Center,CEA,Xi′an 710054,China)

机构地区：[1]中国地震局第二监测中心,西安710054

出　　处：《地震地质》2022年第3期578-589,共12页Seismology and Geology

基　　金：国家自然科学基金(41904082,41874092);中国地震局地震科技星火计划项目(XH214304)共同资助。

摘　　要：文中基于扶边河断裂周边的2条重力和GPS观测剖面数据计算了该地区的重力异常,并利用该异常反演了马尔康-小金地区周边的地壳密度结构与垂向构造应力,分析了该地区的隆升机制;同时结合地质构造背景、历史发震情况及多年尺度的区域流动重力变化资料分析了小金及周边地区的地震危险性。结果表明,马尔康-小金地区周边自由空气异常较模型结果整体偏小,差异中误差为57mGal,EGM2008模型结果在该地区的精度较低。马尔康-小金地区的莫霍面深度约为60km,整体大于Ariy均衡面深度,受到的地壳垂向构造应力整体为正,认为是由于松潘块体向E挤压并受到四川盆地的阻挡,产生向上的垂向构造应力,且青藏高原东缘的抬升主要由挤压隆升所致。此外,小金东部地区位于小金弧形构造带的弧顶区域,存在明显的垂向构造应力变化梯度带,且2018-2021年3a尺度的重力变化显示该地区存在重力变化四象限及变化梯度带,重力变化的量级超过90μGal,分析认为该地区存在发生强震的背景。As part of the frontal edge of the Tibetan plateau,the eastern Tibetan plateau is featured by large-scale active fault systems,intense tectonic movement,and has experienced many devastating earthquakes,which have attracted high attention.The Fubianhe Fault is located inside the Songpan Block of eastern Tibetan plateau,and to its east is the Longmenshan Fault,which is a strong earthquake-prone zone.However,there are less earthquakes having occurred in the area around the Fubianhe Fault,and whether the area around the Fubianhe Fault has potential of strong earthquakes needs to be analyzed based on the crustal stress pattern.In this study,we calculate the Bouguer gravity anomalies by using two profiles with hybrid gravity and GPS observations,analyze the difference between measured gravity anomalies with the EGM2008 model,as well as the crustal density structures and isostatic additional stress(IAS)around Fubianhe Fault based on the Bouguer gravity anomalies.We analyzed the uplift mechanism of eastern Tibetan plateau based on the inverted IAS.At last,we discussed the medium-strong seismic risk in the eastern Xiaojin County of Sichuan Province,based on the IAS,geological active faults,historical earthquakes,and the regional gravity changes from 2018 to 2021.The main conclusions obtained in this study are as follows:(1)The measured free-air gravity anomalies near the Maerkang-Xiaojin range from-230mGal to 180mGal,which is less systematic than the EGM2008 model results,with the difference standard deviation being 57mGal.The measured gravity anomalies would be used to analyze the regional characteristics in the eastern Tibetan plateau,due to the poor accuracy of EGM2008 in this region.The crustal density structure and Moho depth are inversed based on the measured gravity anomalies,and the Moho depth beneath the Maerkang-Xiaojin is approximately 60km.(2)We estimated the isostatic depth in the study region based on the Airy isostatic theory,and the Moho depth beneath the study area is approximately 60km,which is generally

关 键 词：扶边河断裂 重力和GPS观测 重力异常 垂向构造应力 地震危险性 

分 类 号：P315.726[天文地球—地震学]