ULF/ELF magnetic field variations from atmosphere induced by seismicity

摘要

Local variations of the magnetic field in the ULF-ELF frequency range associated with seismicity are studied with the data of more than 3 a observations at Karimshimo complex observatory (latitude 52.83°N, longitude 158.13°E, Kamchatka, Russia). A wideband emission is found to start about 5 d before an earthquake and last until 5 d after it. Seismic ULF/ELF emission in the frequency range of 4–6 Hz as compared with the seismically quiet background has enhanced Phh/Pdd spectral ratio and reduced standard deviation of ellipse orientation angle and the ellipticity, and it has a more linear polarization. Parameters of this emission are studied for more than 30 individual earthquakes and statistically with the superposed epoch method. The reliability of the earthquake predicting hypothesis is verified, and the favorable parameters for the earthquakes together with those for ELF magnetic field are selected. The following earthquake parameters are favorable for this emission: depths H < 50 km, magnitudes MS > 5.5, and epicenter distances R < 300 km. The changes of natural ULF/ELF emissions during the periods of enhanced seismic activity are interpreted as the result of the excitation of additional ULF/ELF emissions in the seismic zone to the east of the observatory or the redistribution of lightning discharges with their possible concentration near the active crust fault. The earthquake prediction hypothesis is verified for the complex field parameter ΔS and proved to be successful.