Seismic responses to an earthquake source in stratified transversely isotropic porous media

Summary The seismoelectric effect is a coupling phenomenon between the seismic wave field and electromagnetic field caused by the electric double layer in a fluid-saturated porous medium. As seismoelectric signals are sensitive to porous medium properties, such as the water saturation, salinity, porosity, and permeability, they have good potential for imaging the structure and estimating underground parameters. In this study, we proposed an inversion method for estimating the salinity using coseismic electric fields generated by electrokinetic effects. The method was established by waveform matching between synthetic and observed coseismic electric signals based on a horizontally layered model. We used an L1 norm measure to construct the regularisation term and achieve a high-resolution layer interface. Subsequently, we applied the first-order Taylor expansion to estimate the sensitivity and used logarithm transformation to constrain the range of parameters and reduce the solution space. Finally, we used an iteratively reweighted least-squares method to solve the final Gauss-Newton type inversion function in each iteration to obtain the model update until the inversion converged. Numerical experiments were conducted to test the resolution, anti-noise ability, and stability of the inversion algorithm. These results demonstrate that the proposed method can effectively recover the salinity structure, which broadens the application of seismoelectric effects. We further applied the method to the Mw 6.5 Jiuzhaigou earthquake in 2017 and used the observed coseismic electric field to estimate the salinity and conductivity beneath the station.

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Semi-analytical simulation of seismic waves generated by a point source in 1-D layered half-space of double-porosity media

Jiang

Gao

Cheng

et al. 2023

Geophysical Journal International

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Summary In this study, we present a semi-analytical method to simulate the propagation of seismic waves in horizontally stratified double-porosity media. We solve the governing equations in the frequency-wavenumber domain and then compute the time-space domain solutions by Hankel transform and fast Fourier transform. We conduct numerical simulations to study the properties of the seismic waves in the double-porosity media. The results show the existence of three P waves, one fast P wave and two slow P waves. The two slow P waves are highly attenuated and can be observed by assuming a low fluid viscosity. By comparing the fast P wave in a single-porosity medium and that in a double-porosity medium, we find that the double-porosity model predicts much higher attenuation of the fast P wave due to the local fluid flow between the background medium and the inclusions. We also study the parameters affecting the attenuation, such as the radius of the spherical inclusions, the viscosity of the pore fluid, the permeability of the background medium and the porosity of the inclusions. Finally, we present a cross-well survey model to investigate the seismic responses in the double-porosity media and compare them with the responses in the single-porosity media. We find that both the amplitude and velocity of the fast P wave decrease with the increase of the volume ratio of the inclusions.

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Seismic responses to an earthquake source in stratified transversely isotropic porous media

Cited by 5 publications

References 42 publications

Three-dimensional axisymmetric transient response of an unsaturated poroelastic transversely isotropic half-space

Three-dimensional axisymmetric transient response of an unsaturated poroelastic transversely isotropic half-space

Estimation of fluid salinity using coseismic electric signal generated by an earthquake

Semi-analytical simulation of seismic waves generated by a point source in 1-D layered half-space of double-porosity media

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