Polarization and propagation property of electromagnetic pulses in the earth

In order to confirm the generations of electromagnetic (EM) pulses in the earth when earthquakes occurred, we have been conducting EM measurements using sensor systems composed of tri-axial magnetic search coils installed at the bottom of 100 m-deep borehole and on the seashore ground. We examined polarizations of magnetic field vectors of EM pulses simultaneously detected at the vertical two positions, and confirmed several kinds of propagation modes. One was vertically incident waves with linear polarization. Using their waveforms, we estimated electrical conductivity, skin-depth and effective phase velocity of the EM pulse in the electrically high conductive medium of the sedimentary layer around the borehole. The second was obliquely incident and ellipsoidal polarized mode, which became Zennek wave propagating along the ground surface, and the third was artificial EM pulses.