洋流的电磁效应及其对大地电磁场的影响  

The Electromagnetic Field Induced by Tide and Its Influence on Magnetotelluric

作　　者：沈昭昂 彭中 杨波 Shen Zhaoang;Peng Zhong;Yang Bo(School of Earth Sciences,Zhejiang University,Hangzhou Zhejiang 310027,China)

机构地区：[1]浙江大学地球科学学院,浙江杭州310027

出　　处：《工程地球物理学报》2022年第5期729-741,共13页Chinese Journal of Engineering Geophysics

基　　金：国家自然科学基金(编号:41830212)。

摘　　要：海底大地电磁观测常受到海洋潮汐、内波或湍流的干扰,为了提高大地电磁数据观测的可靠性,有必要研究洋流运动的感生电磁场对海洋大地电磁观测的影响。本文从麦克斯韦方程组出发,推导了海水运动产生的感应电磁场控制方程,并基于有限体积法计算了包含海水层且考虑了洋流运动的感生电磁场效应的大地电磁响应。同时,以简单洋陆模型和卡斯卡迪亚俯冲带模型为例,对大地电磁响应进行了三维数值模拟。结果表明:观测信号周期越短,靠近洋流活动区域的海底大地电磁场受海水运动的干扰越严重,视电阻率失真现象越明显;陆地一侧的大地电磁场因感生电磁场的快速衰减而几乎未受到海水运动的影响。因此洋流的电磁效应对于海底观测台站会产生较大的干扰,而对陆基台站的观测所带来的影响可以忽略。Seafloor magnetotelluric(MT)observations are often disturbed by ocean tides,internal waves or turbulence.To improve the reliability of magnetotelluric data observation,it is necessary to study the influence of the electromagnetic field induced by ocean current motion.Starting from Maxwell’s equations,this paper deduces the governing equations of the induced electromagnetic field generated by the motion of seawater.Based on the staggered grid finite volume method,we calculate the magnetotelluric response including the sea water layer and the effects of the electromagnetic field induced by the motion of the ocean currents.Taking the simple ocean-continent model and the Cascadia subduction model as examples,the paper simulates the magnetotelluric responses over two electrical resistivity models,a simple ocean-continent model and the other,more realistically,the Cascadia subduction zone model.The modeling results show that:(1)the short periods band of the MT impedance is distorted seriously by the induced electromagnetic field from seawater motion,especially the apparent resistivity curves;(2)the magnetotelluric field on the land side is almost unaffected by the seawater movement due to the rapid attenuation of the induced electromagnetic field.Therefore,the electromagnetic effect of ocean currents causes great interference to submarine observation stations,while the impact on observations of land-based stations can be ignored.

关 键 词：洋流 电磁效应 大地电磁正演 

分 类 号：P631.3[天文地球—地质矿产勘探]