ELECTRIC FIELD VARIATIONS RECORDED ON SEA BOTTOM DURING A SEISMIC PERTURBATION CAUSED BY A DISTANT EARTHQUAKE

Abstract

Studies of electric and magnetic fields in the ocean under different seismic conditions are critically important for understanding how the natural electromagnetic field of the ocean is generated and for quantitatively evaluating the effect of seismic oscillations on instruments. The results of the first such experimental investigations indicate a correlation between the spectrum of electric field variations recorded by an antenna placed on the sea bottom at a depth of 3500 meters and the spectrum of pressure fluctuations at the antenna site. The study presented here gives the results of electric field measurements made simultaneously at ocean depths of 500 and 2000 meters during an earthquake which took place on September 15, 1985 in the New Guinea Islands area, at 2 hours 52 minutes 08 seconds Greenwich Time, as recorded by the seismic station Vladivostok. The measurements were made on the continental slope of the Sea of Japan. The distance between the measurement area and the epicenter of the earthquake was 5200 kilometers. The spectra of the seismic oscillations and of the electric field variations at both depths were very similar in the range of 0.03 to 0.15 Hz during all phases of the earthquake. The observed similarity in electric field spectra and the spectra of seismic oscillations allows to conclude that the recorded electric field variations were seismic in origin. This electric field effect, generated by a small ground shift, attests to the significant influence of seismic processes on the electric field measurements in the ocean.