Seismoelectric imaging of shallow targets

Abstract

We have undertaken a series of controlled field experiments to develop seismoelectric experimental methods for near-surface applications and to improve our understanding of seismoelectric phenomena. In a set of off-line geometry surveys (source separated from the receiver line), we place seismic sources and electrode array receivers on opposite sides of a man-made target (two sand-filled trenches) to record separately two previously documented seismoelectric modes: (1) the electromagnetic interface response signal created at the target and (2) the coseismic electric fields located within a compressional seismic wave. With the seismic source point in the center of a linear electrode array, we identify the previously undocumented seismoelectric direct field, and the Lorentz field of the metal hammer plate moving in the earth’s magnetic field. We place the seismic source in the center of a circular array of electrodes (radial and circumferential orientations) to analyze the source-related direct and Lorentz fields and to establish that these fields can be understood in terms of simple analytical models. Using an off-line geometry, we create a multifold, 2D image of our trenches as dipping layers, and we also produce a complementary synthetic image through numerical modeling. These images demonstrate that off-line geometry (e.g., crosswell) surveys offer a particularly promising application of the seismoelectric method because they effectively separate the interface response signal from the (generally much stronger) coseismic and source-related fields.

Laboratory measurements and theoretical modeling of seismoelectric interface response and coseismic wave fields

“…[3][4][5][6][7] Furthermore, a wide range of field and laboratory validations of the coseismic field and the interface response was presented in the literature. [8][9][10][11][12][13][14][15][16][17][18][19][20][21] Several of these works compare either field measurements 15,17 or laboratory measurements 20 with a seismoelectric wave propagation model, corroborating that the coseismic and interface response fields are predicted by the theory.…”

“…This observation is in agreement with the description of the interface response modeled as the radiation from an oscillating electric dipole oriented vertically with respect to the interface. 3,15 The second pulse at position 6 arrives 5.7 ls later. It travels along with the Pf-wave at approximately 1900 m/s from the front of the sample to position 6.…”

Spectral peaks in electric field at resonance frequencies for seismically excited motion of ions in the Earth’s magnetic field

“…Even for electric field variations associated with the passage of seismic wave, there are many examples (e.g. Thompson and Gist, 1993;Butler et al, 1996;Mikhailov et al, 1997;Beamish, 1999;Garambois and Dietrich, 2001;Haines et al, 2007) as well as theoretical studies (e.g. Pride and Morgan, 1991;Gershenzon, 1992;Pride, 1994;Pride and Haartsen, 1996;Haartsen and Pride, 1997;Garambois and Dietrich, 2002;Huang, 2002;Ren et al, 2010a, b).…”

Modelagem numérica do efeito sismoelétrico em meios 2D

“…No entanto, a dificuldade imposta pelo grande número de parâmetros dos quais depende o sinal sismoelétrico (parâmetros poroelásticos e os parâmetros associados ao coeficiente de acoplamento eletrocinético) impede o uso direto da ferramenta sismoelétrica para determinar tais parâmetros sob condições reais, apesar do sucesso de alguns trabalhos experimentais (Murty, 1985;Thompson & Gist, 1993;Butler et al, 1996;Mikhailov et al, 1997Mikhailov et al, e 2000Zhu et al, 1999;Garambois & Dietrich, 2001;Fourie, 2003;Zhu & Toksöz, 2003e 2005Haines, 2004;Dupuis et al, 2007;Strahser et al, 2007).…”