Seismoelectric wave conversions in porous media: Field measurements and transfer function analysis

Abstract

We present a series of field experiments showing the transient electric fields generated by a seismic excitation of the subsurface. After removing the powerline noise by adaptive filtering, the most prominent feature of the seismoelectric recordings is the presence of electric signals very similar to conventional seismic recordings. In one instance, we identified small‐amplitude precursory electromagnetic disturbances showing a polarity reversal on either side of the shotpoint. Concentrating on the dominant seismoelectric effect, we theoretically show that the electric field accompanying the compressional waves is approximately proportional to the grain acceleration. We also demonstrate that the magnetic field moving along with shear waves is roughly proportional to the grain velocity. These relationships hold true as long as the displacement currents are much smaller than the conduction currents (diffusive regime), which is normally the case in the low‐frequency range used in seismic prospecting. Furthermore, the analytical transfer functions thus obtained indicate that the electric field is mainly sensitive to the salt concentration and dielectric constant of the fluid, whereas the magnetic field principally depends on the shear modulus of the framework of grains and on the fluid’s viscosity and dielectric constant. Both transfer functions are essentially independent of the permeability. Our results suggest that the simultaneous recording of seismic, electric, and magnetic wavefields can be useful for characterizing porous layers at two different levels of investigation: near the receivers and at greater depth.

Remote Detection of the Electric Field Change Induced at the Seismic Wave Front from the Start of Fault Rupturing

“…Moreover, seismograms and electrograms at the observation site correlated well with each other [10,[15][16][17]. Theoretical and observational studies indicated that there were linear relations between the electric field and seismic velocity [10] or acceleration [17], with the coefficient (transfer function) depending on the kinetic property on the site.…”

“…from the ordinary coseismic variation moving with the seismic wave as recorded and studied so far [9,10,12,[14][15][16][17][18][19][20][21][22][23]. This is the first report of the detection of this kind of electric variation, that is, correlation with the seismic wave starting from the beginning of fault rupture, in our long history of electric field measurement by using a borehole antenna.…”

“…At the first stage of the analysis of the phenomenon, the B anomalies (Figure 2(a)) at Hasaki were thought to be well-known coseismic electric variations observed and reported in numerous papers [9,10,12,[14][15][16][17][18][19][20][21][22][23]. They correlated in general with the ground surface fluctuation Figure 1).…”

“…Recent application of seismoelectronics to exploration surveying has resulted in finding and confirming the coseismic electromagnetic field [14][15][16][17]. However, we need more data to understand the phenomenon to build a consistent generation model and to develop application technology based on this phenomenon.…”

“…The seismic wave speed is about 6 km/s for the primary (P) wave and 3.5 km/s for the secondary wave [1,2] in the upper crust. There have been many reports on the electromagnetic phenomena of earthquakes and volcanic eruptions (e.g., [3][4][5][6][7]), but only a few papers have dealt with the field observation of electromagnetic variation that started just after the rupture of the fault [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Belov et al [8] detected associated electromagnetic fields about 10 seconds before the seismic wave arrival and 4 seconds after the origin time.…”