莫克兰俯冲带巨厚沉积层速度结构及含水量分布特征  

Velocity structure and water content characteristics of thick sediments in the Makran subduction zone

作　　者：于传海[1,6] 刘思青 高维 曾信 赵旭 徐敏 YU ChuanHai;LIU SiQing;GAO Wei;ZENG Xin;ZHAO Xu;XU Min(Key Laboratory of Ocean and Marginal Sea Geology,Chinese Academy of Sciences,South China Sea Institute of Oceanology,Guangzhou 510301,China;Key Laboratory of Marine Mineral Resources,Ministry of Natural and Resources,Guangzhou 511458,China;China Aero Geophysical Survey and Remote Sensing Center for Natural Resources,Beijing 100083,China;Center of Ocean Expedition,School of Atmospheric Science,Sun Yat-sen University,Zhuhai Guangdong 519082,China;University of Chinese Academy of Sciences,Beijing 100049,China;China-Pakistan Joint Research Center on Earth Sciences,Marine Subcenter,Islamabad 45320,Pakistan)

机构地区：[1]中国科学院边缘海与大洋地质重点实验室,南海海洋研究所,广州510301 [2]自然资源部海底矿产资源重点实验室,广州511458 [3]中国自然资源航空物探遥感中心,北京100083 [4]中山大学,大气科学学院海洋科学考察中心,广东珠海519082 [5]中国科学院大学,北京100049 [6]中国-巴基斯坦地球科学联合调查中心海洋分中心,伊斯兰堡45320

出　　处：《地球物理学报》2025年第3期1054-1068,共15页Chinese Journal of Geophysics

基　　金：自然资源部海底矿产重点实验室开放基金(KLMMR-2022-G06);国家自然科学基金(42306087,42106077,42106078);广东省基础与应用基础研究基金(2022A1515110879,2021B1515020023);广州市基础与应用基础研究项目(202201010637,202102080211);南海南部重点海域航空重磁精密测量项目(DD20230641)联合资助。

摘　　要：北印度洋莫克兰俯冲带是全球超低角度俯冲、巨厚沉积覆盖、特宽增生楔的俯冲带端元代表,其巴基斯坦海域区段构造特征复杂、大震活动频繁.巨厚沉积层的结构、固结状态及含水量直接影响着俯冲带的板片耦合程度、地震活动与构造演化特征.莫克兰俯冲带海上探测数据有限,沉积分层结构与力学属性仍不清楚,严重制约了其俯冲动力学过程和地震发育机制的研究.本研究基于2018年中巴联合航次获取的主动源海底地震仪数据,通过走时层析成像方法获取了莫克兰俯冲带穿过深海盆地、变形前缘和增生楔的沉积层速度结构,揭示了其孔隙度结构和含水量分布特征.模型结果显示,莫克兰俯冲带输入沉积厚达8.2 km,地震P波速度达4.5 km·s^(-1),4 km埋深之下沉积物固结成岩.莫克兰俯冲带浅部含水量在15 wt%以上,俯冲沉积脱水固结程度较高,含水量在3 wt%以下,高固结沉积可能增加莫克兰俯冲带的大震孕育潜力.The Makran subduction zone,situated in the North Indian Ocean,represents the end-member of subduction zones characterized by an ultralow subduction angle,thick sedimentary coverage and a broad accretionary wedge on a global scale.The offshore segment near Pakistan exhibits intricate tectonic features and experiences recurrent large earthquakes.The structure of the thick sedimentary layers,their consolidation state,and water content play a pivotal role in influencing the degree of slab coupling,seismic activity and the tectonic evolution characteristics within the subduction zone.The limited availability of marine detection data from the Makran subduction zone,coupled with poorly constrained sedimentary stratigraphic architecture and mechanical attributes,severely constrains investigations into its subduction dynamics and seismogenic mechanisms.Based on the active-source ocean bottom seismometer data collected during the 2018 China-Pakistan joint voyage,this study employs travel-time tomography to elucidate the sediment velocity structure across the Makran subduction zone,encompassing the abyssal plain,deformation front,and accretionary wedge.The results reveal the porosity architecture and spatial patterns of water content distribution of the sediments.The obtained model results reveal that the incoming sediments in the Makran subduction zone attain a substantial thickness of 8.2 km,with seismic P-wave velocities reaching a maximum of 4.5 km·s−1.Significantly,the sediments undergo consolidation into diagenetic phases below a burial depth of 4 km.The water content in the shallow section of the Makran subduction zone exceeds 15 wt%,while the subducted sediments indicate heightened levels of dehydration and consolidation,resulting in water content diminishing to less than 3 wt%.The highly consolidated nature of subducting sediments may facilitate the seismogenic potential of significant earthquakes within the Makran subduction zone.

关 键 词：莫克兰俯冲带 沉积层 速度结构 孔隙度 孕震潜力 

分 类 号：P738[天文地球—海洋地质]