Evidence of the theoretically predicted seismo-magnetic conversion

Abstract

We acknowledge the Geophysical Journal International and the Association/Society and Blackwell Publishing. The definitive version is available at www.wileyinterscience.com. The reference is : Bordes, C., L. Jouniaux, S. Garambois, M. Dietrich, J.-P. Pozzi, and S. Gaffet, Evidence of the theoretically predicted seismo-magnetic conversion, G.J.I., 174, issue 2, 489-504, doi:10.1111/j.1365-246X.2008.03828.xInternational audienceSeismo-electromagnetic phenomena in porous media arise from seismic wave-induced fluid motion in the pore space, which perturbs the equilibrium of the electric double layer. This paper describes with details the original experimental apparatus built within the ultra-shielded chamber of the Low Noise Underground Laboratory of Rustrel (France). We measured seismo-magnetic conversions in moist sand using two induction magnetometers, and a pneumatic seismic source to generate the seismic wave propagation. We ensured to avoid the magnetometer vibrations, which could induce strong disturbances from induction origin. Interpretation of the data is improved by an analytical description of phase velocities for fast (P_f) and slow (P_s) longitudinal modes, transverse mode (S) as well as the extensional mode due to the cylindrical geometry of the sample. The purpose of this paper is to provide elements to measure correctly co seismic seismomagnetic fields and to specify their amplitude. The seismic arrivals recorded in the sample showing a 1200$-1300 m/s velocity have been associated to P and extensional waves. The measured seismo-magnetic arrivals show a velocity of about 800 m/s consistent with the calculated phase velocity of S waves. Therefore we show that the seismo-magnetic field is associated to the transverse part of the propagation, as theoretically predicted by Pride (1994), but never measured up to now. Moreover, the combined experimental and analytical approaches lead us to the conclusion that the measured seismo-magnetic field is probably about 0.35 nT for a 1 m/s2 seismic source acceleration (0.1 g)

Coupled seismic and electromagnetic wave propagation

“…These effects have been verified experimentally in the laboratory (e.g., Zhu et al, 1999Zhu et al, , 2000Zhu & Toksöz, 2003;Block & Harris, 2006;Bordes et al, 2006) and in the field (e.g., Long & Rivers, 1975;Butler et al, 1996;Mikhailov et al, 1997;Beamish, 1999;Garambois & Dietrich, 2001;Dupuis et al, 2007;Haines et al, 2007). Also, the coseismic magnetic fields associated with a Stoneley wave (Zhu & Toksöz, 2005) and with a shear wave have been measured (Bordes et al, 2006(Bordes et al, , 2008. Electrokinetic theory combines poroelastic and EM theory through coupling in flux/force relations.…”

“…A wide range of field and laboratory measurements of the coseismic and interface response fields was presented (see e.g., Martner & Sparks, 1959;Thompson & Gist, 1993;Butler et al, 1996;Mikhailov et al, 1997;Beamish, 1999;Zhu et al, 1999;Mikhailov et al, 2000;Zhu et al, 2000;Garambois & Dietrich, 2001;Zhu & Toksöz, 2003, 2005Block & Harris, 2006;Bordes et al, 2006;Dupuis & Butler, 2006;Haines et al, 2007;Dupuis et al, 2007;Strahser et al, 2007;Liu et al, 2008;Zhu et al, 2008a,b;Dupuis et al, 2009). Zhu & Toksöz (2005) and Bordes et al (2006Bordes et al ( , 2008 reported on coseismic magnetic field measurements associated with a Stoneley wave and a shear wave, respectively. The inverse effect was also measured.…”

A review on electrokinetically induced seismo-electrics, electro-seismics, and seismo-magnetics for Earth sciences

“…Note that it has been already suggested to monitor the magnetic field in boreholes to detect fluid flow variations in an accretionary prism . Bordes et al (2006Bordes et al ( , 2008 showed the existence of seismomagnetic conversions, predicted by the theory since 1994. The authors developed an experimental set-up with a remotecontrolled seismic source, to induce seismic wave propagation in a saturated sand column (Fig.…”

“…When performing magnetic measurements it is necessary to use nonmetallic materials, because of their possible even small displacements within the ambient magnetic field. Measurements performed on dry samples showed that both the electric field and the magnetic field are within the noise level (Zhu et al, 2000;Bordes et al, 2008).…”

“…Although the oil conductivity is Figure 22. Scheme of the experiment developed in the underground laboratory of Rustrel to measure the magnetic part of the SEM conversions (from Bordes et al, 2008). lower than the water conductivity, the electric contrast between the water-saturated sandstone and oil may be lower than the one between the water-saturated sandstone and the water, leading to a decrease of the amplitude of the IR.…”