中国南北地震带北段及其周缘地壳厚度与泊松比研究  

Crustal thicknesses and Poisson's ratios beneath the northern section of the north-south seismic belt and surrounding areas in China

作　　者：王兴臣[1,2] 丁志峰[1,2] 武岩[1,2] 朱露培 

机构地区：[1]中国地震局地球物理研究所,北京100081 [2]中国地震局地球物理研究所地震观测与地球物理成像重点实验室,北京100081 [3]Department of Earth and Atmos. Sciences,Saint Louis University

出　　处：《地球物理学报》2017年第6期2080-2090,共11页Chinese Journal of Geophysics

基　　金：国家自然科学基金(41404069;41404074);地震行业科研专项(201308011)联合资助

摘　　要：本文利用中国地震科学探测台阵2013-2015年在南北地震带北段及其周缘架设的673个台站所记录到的远震波形所提取到的接收函数并应用H-κ扫描方法获取了南北地震带北段及其周缘的地壳厚度和泊松比,结果显示研究区地壳厚度从青藏高原东北缘向鄂尔多斯块体逐渐减小,从65 km逐渐减薄至40 km,不同块体之间地壳厚度存在明显差异.祁连造山带西部地壳厚度超过60 km,而东部地壳厚度仅为约50 km左右,表明祁连造山带东、西部地壳增厚变形存在着明显差异.西秦岭造山带地壳厚度从60 km减薄到40 km,其东部具有较薄的地壳厚度可能经历了拆沉.阿拉善块体作为华北克拉通西部块体的一部分,西部地壳厚度约50 km,而东部约45 km,表明阿拉善块体西部由于印度一欧亚板块碰撞也受到了活化改造,其克拉通性质只在其中东部残留.研究区泊松比变化范围为0.20~0.31,平均泊松比约0.25,表明地壳主要由长英质矿物组成,较高的泊松比主要分布在六盘山断裂带和银川一河套地堑.研究结果显示地壳厚度与高程之间具有较好的相关性,表明地壳整体上处于相对均衡的状态,而西秦岭造山带和祁连造山带东部的部分区域地壳可能处于不均衡状态.We conducted H-κ stacking of receiver functions using teleseismic data from 673 stations of ChinArray in 2013—2015 and produced a unified and detailed map of crustal thicknesses and Poisson＇s ratios of the northern section of the north-south seismic belt and surrounding areas in China. Results show that the crust thickens from about 40 km in the Ordos plateau to about 65 km in the northeast margin of the Tibetan plateau. Thick crust （about 60 km） appears beneath the western Qilian orogenic belt. In contrast, the crust is relatively thin （about 50 km） beneath the eastern Qilian orogenic belt, suggesting significant difference in crustal shortening and thickening between the western and eastern parts of the Qilian orogenic belt. The crustal thickness in the western Qinling orogenic belt decreases from west （about 60 km） to east （about 40 km）. The thin crust implies that the eastern Qinling orogenic belt might have experienced delamination. As part of the western North China craton, the Alxa block＇s crustal thickness is about 50 km in the west and about 45 km in the east, respectively, indicating that the crustal structure beneath the western Alxa block has been modified possibly associated with the Indo—Eurasian collision while the eastern Alxa block has most likely preserved its old cratonic root. The Poisson＇s ratio of the study area varies from 0.20 to 0.31, with an average value of 0.25, consistent with a felsic composition of the crust. The high Poisson＇s ratio is present along the Liupanshan thrust belt and Yinchuan—Hetao graben. Our results show a close correlation between crustal thickness and topography, which indicates that the crust is in an approximately isostatic equilibrium in the study area. Our results also suggest that the crust may not be in an isostatic equilibrium both in the eastern Qinling orogenic belt and eastern Qilian orogenic belt.

关 键 词：中国地震科学台阵观测 南北地震带 地壳结构 接收函数 泊松比 

分 类 号：P315[天文地球—地震学] P541[天文地球—固体地球物理学]