青藏高原东南缘重力场多尺度分析及其构造含义  

MULTI-SCALE ANALYSIS OF THE GRAVITY FIELD IN THE SOUTHEASTERN QINGHAI-TIBET PLATEAU AND ITS TECTONIC IMPLICATIONS

作　　者：方东 胡敏章[1,2] 郝洪涛 FANG Dong;HU Min-zhang;HAO Hong-tao(Key Laboratory of Earthquake Geodesy,Institute of Seismology,China Earthquake Administration,Wuhan 430071,China;Institute of Disaster Prevention,Langfang,Hebei 065201,China)

机构地区：[1]中国地震局地震研究所,地震大地测量重点实验室,武汉430071 [2]防灾科技学院,廊坊065201

出　　处：《地震地质》2021年第5期1208-1232,共25页Seismology and Geology

基　　金：基国家自然科学基金(41974021);中国地震局地震科技星火计划项目(XH20039)共同资助。

摘　　要：文中利用小波多尺度分析方法对青藏高原东南缘WGM2012布格重力异常进行5阶分解,得到了该区域不同深度上的布格重力异常子集,并据此研究了该区域的地壳构造、物质运动及其孕震环境。结果表明:2、3阶小尺度重力异常反映了该地区的强震主要发生在高重力梯级带及活动地块边界上,对比分析各尺度重力异常,发现地震孕育不仅受控于中、上地壳的断裂地块构造,也与深部地壳的密度变化有关,这种地壳深、浅部相互作用的动力学过程可能是川滇地区地震孕育的重要条件;4阶中尺度重力异常显示松潘-甘孜地块的东南缘存在1个低布格重力异常圈闭,与巴颜喀拉地块地壳中存在着较厚的低速、低阻层的观测结果一致,推测可能与该地块东部岩石圈厚度大、下地壳温度较高、中下地壳部分岩体在高温下熔融有关。在攀枝花地区存在1个高布格重力异常圈闭,推测可能是在攀西古裂谷时期,深部高密度物质上涌过程中在中下地壳的物质残留所致;5阶大尺度重力异常显示在川滇菱形块体呈区域性负重力异常,为青藏高原东南缘“下地壳流”的存在提供支持证据。Since the Cenozoic,the Qinghai-Tibet plateau is uplifting sharply due to the India-Eurasian violent collision.Its crust has thickened accompanied with north-south shortening and east-west extrusion.The eastward-moving material beneath the southeastern margin of Qinghai-Tibet plateau is stopped by hard blocks such as Alax,Ordos and South China block.Under the interaction,a complex structural belt of north-south direction is formed,called the North-south structural belt.And it is also known as the“North-South Seismic Belt”because of dense distribution and high intensity of earthquakes.Therefore,studies of the crustal structure and mass movement characteristics have scientific significance to reveal the mechanism of tectonic activity and earthquake incubation beneath the southeastern Qinghai-Tibet plateau.It will help improve capabilities of regional earthquake preparedness and disaster mitigation.Firstly,the simulation test of simple geological body is carried out to verify the effectiveness of wavelet multi-scale analysis method in gravity field separation and the stability of the application program.When designing a simple geological body model,both the superposition effect of geological bodies at different depths and the decomposition effect of the test model are considered.The approximate field source depth of the separated regional field and local field is calculated by radial logarithmic power spectrum,and the calculation results are consistent with the design depth.It is determined that the wavelet base is“bior3.5”and the decomposition order is 5.The test results show that the“bior3.5”wavelet basis can effectively separate the regional and local anomalies in the geological body of the combined model,and obtain an ideal separation effect.Then,based on the global gravity field model WGM2012 data,the Bouguer gravity anomaly data in the southeastern Qinghai-Tibetan plateau is decomposed in the 5 orders by using multi-scale wavelet analysis,and the radial logarithmic power spectrum is used to analyze

关 键 词：青藏高原东南缘 小波多尺度分析 地壳构造 物质运动 孕震环境 

分 类 号：P315.726[天文地球—地震学]