Anomalous pre-seismic transmission of VHF-band radio waves resulting from large earthquakes, and its statistical relationship to magnitude of impending earthquakes

Abstract

To confirm the relationship between anomalous transmission of VHF-band radio waves and impending earthquakes, we designed a new data-collection system and have documented the anomalous VHF-band radio-wave propagation beyond the line of sight prior to earthquakes since 2002 December in Hokkaido, northern Japan. Anomalous VHF-band radio waves were recorded before two large earthquakes, the Tokachi-oki earthquake (Mj= 8.0, Mj: magnitude defined by the Japan Meteorological Agency) on 2003 September 26 and the southern Rumoi sub-prefecture earthquake (Mj= 6.1) on 2004 December 14. Radio waves transmitted from a given FM radio station are considered to be scattered, such that they could be received by an observation station beyond the line of sight.A linear relationship was established between the logarithm of the total duration time of anomalous transmissions (Te) and the magnitude (M) or maximum seismic intensity (I) of the impending earthquake, for M4-M5 class earthquakes that occurred at depths of 48-54 km beneath the Hidaka Mountains in Hokkaido in 2004 June and 2005 August. Similar linear relationships are also valid for earthquakes that occurred at different depths. The relationship was shifted to longer Te for shallower earthquakes and to shorter Te for deeper ones. Numerous parameters seem to affect Te, including hypocenter depths and surface conditions of epicentral area (i.e. sea or land). This relationship is important because it means that pre-seismic anomalous transmission of VHF-band waves may be useful in predicting the size of an impending earthquake. © 2009 The Authors Journal compilation © 2009 RAS.