HR: 0800h
AN: T51B-0454    [Abstracts]
TI: Ionospheric Penetration of ELF/VLF Electromagnetic Waves Radiated From an Earthquake
AU: * Ozaki, M
EM: ozaki@reg.is.t.kanazawa-u.ac.jp
AF: Graduate School of Natural Science & Technology, Kanazawa University, 2-40-20 Kodatsuno, Kanazawa, 920-8667 Japan
AU: Nagano, I
EM: nagano@reg.is.t.kanazawa-u.ac.jp
AF: Graduate School of Natural Science & Technology, Kanazawa University, 2-40-20 Kodatsuno, Kanazawa, 920-8667 Japan
AU: Yagitani, S
EM: yagitani@reg.is.t.kanazawa-u.ac.jp
AF: Graduate School of Natural Science & Technology, Kanazawa University, 2-40-20 Kodatsuno, Kanazawa, 920-8667 Japan
AU: Miyamura, K
AF: PFU Ltd., Nu 98-2 Unoke, Kahoku, 929-1192 Japan
AB: Theoretical calculations for electromagnetic waves associated with earthquakes have been proposed to analyze the detailed mechanisms and the effects of them. In this study, we compute rigorously the wave intensities in the magnetized ionosphere radiated from an underground current source by using full-wave analysis. We assume that a seismic source is a large electric dipole located underground as the combination of much smaller dipole polarizations created around epicenter. Full-wave analysis has been developed to calculate rigorously the VLF wave propagation in the ionosphere and is extended to analyze the spherical waves radiated from the underground source, which are expanded into a large number of elementary plane waves by using the spherical Bessel function. The effects of the geomagnetic field on the ionospheric wave propagation are considered. The computed results in the frequency range from 10 Hz to 10 kHz show the difference in spatial distributions of the wave intensities due to the whistler-mode propagation. The wave power tends to increase as the frequency decreases, caused by the skin depth effect where lower frequency waves would be less attenuated in the ground medium. In our computation, we see that the magnetic filed is 10$^{-5}$ nT/Hz$^{1/2}$ at the altitude of 200 km in the ionosphere when a 10-kA$\cdot$m current moment is assumed to be created 10 km underground.
DE: 2400 IONOSPHERE
DE: 2487 Wave propagation (6934)
DE: 0619 Electromagnetic theory
DE: 0644 Numerical methods
DE: 0903 Computational methods, potential fields
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting