Anomalies of LF signal during seismic activity in November–December 2004

Abstract

Abstract.A signal transmitted by Japan Time Standard LF station (40 kHz, Fukushima prefecture) and recorded in Petropavlovsk-Kamchatski (Russia) is analyzed during a time interval from 1 July 2004 till 24 January 2005. This interval is characterized by quiet seismic conditions up to the beginning of November, but rather strong seismic activity occurs in November and December not far from Hokkaido (Japan) and in the region of northern Kuril Islands. There were three series of earthquakes with M=5.6-7.1 in a zone of sensitivity of our wave path during two months. Nighttime "bay-like" phase and amplitude anomalies of the LF signal are observed several days before and during every series of earthquakes. During the whole period of seismic activity a significant shift in terminator times is also evident. The spectrum of LF seismo-induced anomalies shows a clear increase for the period of about 25 min.

Observation evidences of atmospheric Gravity Waves induced by seismic activity from analysis of subionospheric LF signal spectra

“…The next LF anomalies were observed before earthquakes December, 18 and 21 (M=5.8 and M=5.6). During the whole period of seismic activity a significant shift in terminator times was also evident (in detail Rozhnoi et al, 2005).…”

“…As to magnetically disturbed days the shift in lower frequencies, typical for seismically disturbed days, is not revealed (Rozhnoi et al, 2005(Rozhnoi et al, , 2006.…”

“…2). In previous works we have applied the spectral analysis to several cases of seismically disturbed days (Rozhnoi et al, , 2005. It was found that the maximum of a spectrum had the period about 20-25 min (0.7-0.8 mHz).…”

Disturbances in a VLF radio signal prior the <i>M</i>=4.7 offshore Anzio (central Italy) earthquake on 22 August 2005

“…More precisely, it was verified that the epicenter is inside the 5th Fresnel zone of the FR-Bari path. It must be noted that the quoted zone is considered to be the most sensitive to the seismo-atmospheric effects (Hayakawa et al, 1996;Molchanov and Hayakawa, 1998;Rozhnoi et al, 2005).…”

“…In last years seismic disturbances in VLF (3-30 kHz)/LF (low band, 30-80 kHz) radio signals, as well as in LF (high band, 150-300 kHz) radio broadcasts, have been presented (Biagi et al, 2001a, b;Biagi and Hayakawa, 2002;Gufeld et al, 1992;Hayakawa and Sato, 1994;Hayakawa et al, 1996Hayakawa et al, , 2006Molchanov and Hayakawa, 1998;Rozhnoi et al, 2005;Rozhnoi et al, 2006a, b). Recently, some possible seismic disturbances revealed by VLF radio signals collected on board of the French DEMETER satellite, were presented by Molchanov et al (2006) and Rozhnoi et al (2007).…”