海底沉积物对近海大地电磁响应的畸变影响与压制:以华南雷琼地区为例  

Distortion of inland magnetotelluric responses by marine sediments and its suppression:A case study from the Lei-Qiong area in South China

作　　者：李鑫 程远志[2] 陈超健 魏雨浓 邓阳凡[1] 胡久常[5] 白登海[2] LI Xin;CHENG YuanZhi;CHEN ChaoJian;WEI YuNong;DENG YangFan;HU JiuChang;BAI DengHai(State Key Laboratory of Deep Earth Processes and Resources,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China;Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;School of Geosciences and Info-Physics,Central South University,Changsha 410083,China;Ludwig-Maximilians University of Munich,Munich 80333,Germany;Earthquake Administration of Hainan Province,Haikou 570273,China)

机构地区：[1]中国科学院广州地球化学研究所深地过程与战略矿产资源全国重点实验室,广州510640 [2]中国科学院地质与地球物理研究所,北京100029 [3]中南大学地球科学与信息物理学院,长沙410083 [4]慕尼黑大学地球与环境科学学院,德国慕尼黑803335 [5]海南省地震局,海口570203

出　　处：《地球物理学报》2025年第4期1381-1393,共13页Chinese Journal of Geophysics

基　　金：国家重点研发计划青年科学家项目(2024YFF0809600);广东省基础与应用基础研究基金(2023A1515012852);国家自然科学基金项目(42004063,42322401,U24A20602);中国科学院战略性先导科技专项课题(XDA0430203);中国科学院广州地球化学研究所“一四五”规划布局项目(E2510315);同位素地球化学国家重点实验室科研启动项目(SKLaBIG-QD-22-05)联合资助。

摘　　要：海洋和陆地之间显著的导电性差异会造成海岸线附近天然时变电磁场的畸变,从而影响近海大地电磁测深(MT)成像结果及解释的可靠性.前人针对高导海水对近海MT响应的影响和校正已开展大量研究,但对海水之下高导沉积物的相关影响仍缺乏认识.为此,本研究基于实测海水深度及海底沉积物厚度数据构建了华南大陆南缘雷琼地区的高分辨率三维海陆电性结构模型,利用有限差分法数值计算和分析了海底沉积物对陆内近海MT响应的影响.结果表明:(1)由于雷琼地区海底沉积物厚度远大于海水深度,近海低频MT响应受到的强烈畸变影响主要来自海底沉积物;(2)相对海南岛,雷州半岛陆内MT响应受到海底沉积物的影响更为严重;(3)海底沉积物造成的畸变影响强度和周期范围主要受控于测点与海岸线的距离、沉积物厚度及陆地深部电性结构.理论模型反演试验表明,忽略海底沉积物的影响会造成近海MT成像结果的严重畸变,而通过将实测海底沉积物三维分布纳入反演初始-先验模型可有效压制畸变影响,获得更可靠的地下电性结构.The presence of significant difference in electrical conductivity between land and ocean can strongly alter the distribution of natural time-varying electromagnetic fields near the coastline,thus affecting the accuracy and reliability of inland magnetotelluric(MT)results and interpretation.Numerous studies have been conducted on the effects and correction of high-conductivity seawater on the MT responses,but the relevant influence of the submarine conductive sediment remains unclear.To address this issue,we constructed a high-resolution threedimensional sea-land model of the Lei-Qiong area at the southern margin of the South China continent based on realistic seawater depth and sediment thickness measurements.We then used the finite difference numerical method to simulate and analyze the impact of marine sediment on the inland MT responses.The simulation results show that:(1)Since the sediment thickness in the study area is much larger than that of seawater,the strong coast effect observed in the low-frequency MT responses mainly come from the marine sediments;(2)In comparison to the Hainan Island,the MT responses within the Leizhou Peninsula are more severely distorted by the marine sediment;(3)The magnitude and period range of the influence caused by marine sediments are primarily determined by factors such as the distance of the MT site from the coastline,the sediment thickness and the subsurface electrical structure beneath the land.

关 键 词：大地电磁测深 海岸效应 海底沉积物 三维数值模拟 电导率结构 

分 类 号：P631[天文地球—地质矿产勘探]