东昆仑断裂带玛沁—玛曲段晚第四纪构造活动特征的地貌响应定量研究  

QUANTITATIVE ANALYSES OF GEOMORPHOLOGIC FEATURES IN RESPONSE TO LATE QUATERNARY TECTONIC ACTI-VITIES ALONG THE MAQIN-MAQU SEGMENT,EAST KUNLUN FAULT ZONE

作　　者：李昭 付碧宏 LI Zhao;FU Bi-hong(Aerospace Information Research Institute,Chinese Academy of Sciences,Beijing 100094,China;University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院空天信息创新研究院,北京100094 [2]中国科学院大学,北京100049

出　　处：《地震地质》2022年第6期1421-1447,共27页Seismology and Geology

基　　金：第2次青藏高原科学考察综合研究(2019QZKK0901)资助。

摘　　要：位于东昆仑断裂带东段的玛沁—玛曲段主断裂带由数条规模不等、羽状斜列的次级断裂组成,其晚第四纪滑动速率自西向东呈现梯度式降低的原因仍存在较大争议。精确查明玛沁—玛曲段主断裂带及其分支断裂的几何学和运动学特征,可为探讨东昆仑断裂带东段的构造转换机制、评价地震危险性提供重要线索。地貌指数定量分析是活动构造研究中的重要方法之一。其中,面积-高程积分(HI)和河流坡降指数(SL)可有效揭示区域构造变形信息,而地势起伏度(TR)能直观地反映区域构造活动的侵蚀响应程度。文中利用30m精度的AW3D30数据系统地定量提取玛沁—玛曲段主断裂带及其周边整个流域的TR指数、流域盆地的HI指数及主要河流的Hack剖面、SL指数及归一化坡降指数(SLK),通过构造地貌与河道形态揭示区域构造活动的地貌响应特征,探讨不同构造段落的活动强度。研究结果表明,沿玛沁—玛曲段主断裂带的HI指数、Hack剖面、SLK指数及TR指数等值呈自西向东连续下降的变化特征,其中,HI值自西部的0.77~0.89向E下降至0.15~0.36,TR所反映的地表侵蚀量从欧拉秀玛乡西侧的400m向E降至玛曲县东侧的(61±11)m,而Hack剖面的上凸程度与其SLK异常显著性则具有西高东低的分布特征,这与沿主断裂带晚第四纪滑动速率自西向东梯度递减的趋势基本一致,表明地貌指数值变化与断裂活动强度密切相关;地貌指数的空间分布差异性揭示了玛沁—玛曲段主断裂带及分支断裂(阿万仓断裂和尕海断裂)的晚第四纪构造活动性具有西段最强,中段、东段逐渐减弱的显著分段特征。结合野外构造地貌调查和验证认为,玛沁—玛曲段主断裂带的晚第四纪活动性从玛沁—欧拉秀玛一带的断裂交会区开始向E逐渐减弱。因此,推断东昆仑断裂带玛沁—玛曲段晚第四纪左旋走滑速率向E降低的现象与其主断裂带The Maqin-Maqu segment(MMS)of the East Kunlun fault zone(EKLF)is located in the seismic gap with a high seismic risk.Study on the geometric characteristics and late Quaternary differential tectonic activity of MMS is critical for carrying out the seismic risk assessment of the cities and towns with relatively high population like the Maqin and Maqu County in the eastern part of EKLF.Previous studies indicated that the late Quaternary left-lateral slip rate along MMS shows an eastward gradient decreasing.However,the geodynamic mechanism to explain this gradient decreasing of slip rate remains controversial.Therefore,accurately identifying the geometric and kinematic characteristics of the major fault zone of MMS and its branch faults can provide important clues for understanding the tectonic transformation mechanism and its seismic risk assessment along the eastern part of EKLF.The geomorphic index can quantitatively describe the geomorphologic characteristics,and effectively extract the active tectonic deformation from surface landscapes.The hypsometric integral index(HI)can well reveal the spatial distribution of the regional tectonic activity intensity by calculating the current three-dimensional volume residual rate of drainage basins.The stream-length gradient index(SL)can effectively reflect the regional tectonic deformation by identifying the geomorphic anomalies of river longitudinal profiles.And the topographic relief(TR)can directly evaluate the geomorphologic erosion in response to the regional tectonic activity.These geomorphic indices have been widely used to differentiate active tectonic deformation regionally.In this study,the geological and geomorphic interpretation of high-resolution remote sensing images are employed to determine the spatial distribution and geometrical features of the major fault zone and branch faults of MMS.The 30m AW3D30 data is used to extract systematically 69 drainage basins along the MMS and adjacent area by GIS spatial analysis technology.Our results indicate that the HI

关 键 词：面积-高程积分 地势起伏度 河流坡降指数 构造活动强度 东昆仑断裂带东段 

分 类 号：P315.2[天文地球—地震学]