含起伏地形地层中点源激发的震电响应研究  

Seismoelectric response to a point source in the media with undulating topography

作　　者：高玉涛 高永新 何晓[2] 王军[3] 姚程 GAO YuTao;GAO YongXin;HE Xiao;WANG Jun;YAO Cheng(School of Civil Engineering,Hefei University of Technology,Hefei 230009,China;State Key Laboratory of Acoustics,Institute of Acoustics,Chinese Academy of Sciences,Bejing 100190,China;Department of Astronautics and Mechanics,Harbin Institute of Technology,Harbin 150001,China)

机构地区：[1]合肥工业大学土木与水利工程学院,合肥230009 [2]中国科学院声学研究所声场声信息国家重点实验室,北京100190 [3]哈尔滨工业大学航天科学与力学系,哈尔滨150001

出　　处：《地球物理学报》2020年第5期2069-2083,共15页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(41774048,41674121,41974136);中央高校基本科研业务费专项资金资助项目(PA2018GDQT0008)资助.

摘　　要：地震诱导电磁现象是国内外地学领域十分关注的前沿问题,前人对地震波和电磁场耦合波场的认识主要是基于规则模型获得的.为研究含起伏地表和地下界面的地层中震电波场激发、传播特性,本文采用有限元软件COMSOL Multiphysics模拟点震源激发的电磁场.首先给出频率域二维SHTE模式震电耦合方程组,然后利用COMSOL软件建立计算模型,并求解出点力源激发震电波场的频率域响应,最后利用FFT变换得到地震波场和电磁场的时间域波形.模拟结果表明,震电波场中存在三种类型的电磁信号,第一种是震源直接激发的电磁波;第二种是地震波在分界面处激发的电磁波(包括自由表面、地下不同介质分界面);第三种是伴随地震波的同震信号,前两种电磁波比地震波更早到达远处观测台站,对地震预警有重要意义.此外,研究还发现:当地震波传播至地表并沿着地表传播时,在地表附近空气层中同样记录到了伴随地震波传播的电磁扰动信号,该信号与相同水平源距条件下、地下观测点接收到的电磁信号相同,这与前人的一些观测结果相符.本文研究结果为今后地震电磁信号的解释提供了理论证据.Study on earthquake-induced electromagnetic(EM)phenomena is an important subject in geosciences.Previous understanding of the seismoelectric coupled wavefields is mainly based on the simulations for regular model.In order to study the excitation and propagation characteristics of the coupled seismic and EM wave field in the media with undulating topography,we use the finite element software COMSOL Multiphysics to simulate the electromagnetic field excited by a point source.Firstly,we present the two-dimensional SHTE mode equations in frequency domain.Then the COMSOL software is used to establish the computational model and solve the frequency-domain response of the seismoelectric wave fields.Finally,the time-domain waveforms of the seismic and electromagnetic fields are obtained by applying the fast Fourier transformation.The simulations show that there are three types of EM signals.The first one is the direct EM wave excited by the source;the second is the EM wave excited by the seismic wave at interfaces(including the free surface,the underground interfaces separating different media);The third one is a coseismic EM signal accompanying a seismic wave.The former two kinds of EM waves reach the distant observation station earlier than the seismic wave,and thus they are important for earthquake early warning.The results also show that when the seismic waves propagate along the surface,they also cause EM fields in the air layer.We observe the same EM signals at the receivers in the air and underground medium near the surface.Such a phenomenon agrees with some previous observations.The results in this study provide theoretical evidence for interpreting the earthquake-associated EM signals in the future.

关 键 词：动电效应 地震波 电磁场 起伏地形 数值模拟 

分 类 号：P319[天文地球—固体地球物理学]