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Next: Synthetic Electroseismic data Up: Haines and Guitton: Electroseismics Previous: Haines and Guitton: Electroseismics

Introduction

Electroseismic phenomena produce two forms of energy: the interface response signal, and the coseismic noise Haines and Guitton (2002). Electroseismic data processing must attenuate the coseismic noise in order to reveal the interface response. In short, the signal is composed of flat events (the interface response has virtually zero moveout) while the noise (coseismic energy) has moveout similar to seismic data. The object is to remove the curved energy so that it does not contaminate the final stack of the gather. We employ the signal/noise separation technique described by Guitton (2003) to test its effectiveness in electroseismic processing. The basic approach is to estimate non-stationary prediction-error filters (PEF's) for the signal and the noise, and to use these PEF's in an iterative signal/noise separation following Guitton et al. (2001).

The electroseismic signal is far weaker than the noise so we can not hope to obtain an adequate model for the estimation of signal PEF's by muting in the parabolic radon transform (PRT) domain, or other alterations of the original data. We can, however, take advantage of the fact that the amplitude pattern of the signal can be easily modeled. It is the pattern of the potential (V) of a dipole field:  
 \begin{displaymath}
V(x,z) = \frac{qd}{4\pi\epsilon_0} \,
 \frac{z}{(x^2+z^2)^{3/2}},\end{displaymath} (1)
as measured at a horizontal offset x from a dipole at depth z, where q is the magnitude of the electrical charges, d is the distance between the two separated charges, and $\epsilon_0$ is the electrical permittivity of the Earth. Using a velocity model to provide the relationship between depth and travel time, and making basic assumptions about the size of the Fresnel zone producing the dipole, we can compute a model of the relative amplitude measured at various locations for events corresponding with any given travel time. This amplitude pattern may be used directly in the estimation of one-dimensional (in the offset direction) PEF's (since such a one-dimensional PEF contains no wavelet information), or we can use the amplitude pattern to scale synthetic wavelets to be used as models for PEF estimation. Thus if we have a velocity model for a particular study area, we can estimate non-stationary signal PEF's to target any interface response events that may be in the data without the need for a priori knowledge of their arrival times. We use simple physics [equation (1)] to design general signal PEF's, and use components of the original data to design noise PEF's. We show that these non-stationary PEF's provide an effective means for separating the interface response signal from the coseismic noise in synthetic and real electroseismic data.


next up previous print clean
Next: Synthetic Electroseismic data Up: Haines and Guitton: Electroseismics Previous: Haines and Guitton: Electroseismics
Stanford Exploration Project
7/8/2003