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PRECURSORY SIGNATURE OF THE KOBE EARTHQUAKEON VLF SUBIONOSPHERIC SIGNAL

1996; Volume: 16; Issue: 3 Linguagem: Inglês

10.1541/jae.16.247

0919-2050

Masashi Hayakawa, O. A. Molchanov, T. Ondoh, Eiji Kawai,

earthquake and tectonic studies

The subionospheric VLF Omega signal transmitted from Tsushima, Japan (geographic coordinates: 34°37'N, 129°27'E) is continuously received at Inubo (35°42'N, 140°52'E), and the propagation characteristics (especially phase) of this signal have exhibited abnormal behaviour (especially around the sunrise and sunset local times) a few days before the main shock of the 1995 Hyogo-ken N anbu earthquake.A statistical study based on long-term (four months before and four months after the earthquake) observational data has strongly suggested that this anomaly was not coincidental, but it is highly likely to be related to the earthquake.We have found from a computer simulation of VLF signal propagation that this observed effect can be explained by a decrease of about 1.5 km in the VLF reflection height.Plausible mechanisms for this decrease are discussed.