An overview on preseismic anomalies in LF radio signals revealed in Italy by wavelet analysis

T Maggipinto T Maggipinto,L Castellana L Castellana,P F Biagi P F Biagi,A Ermini A Ermini

doi:10.4401/ag-4445

T Maggipinto T Maggipinto, L Castellana L Castellana + Show 2 more

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https://doi.org/10.4401/ag-4445

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Abstract

Since 1996, the electric field strength of the two broadcasting stations MCO (f=216 kHz, southeast France) and CZE (f=270 kHz, Czech Republic) has been sampled every ten minutes by a receiver (AS) located in central Italy. Here, we review the results obtained by a detailed analysis applied to the data recorded from February 1996 up to December 2004. At first, the daytime and nighttime data were extracted and then, in the daytime da- ta, the data collected in winter were separated from those collected in summer. On the second step the wavelet transform was applied. The results of this analysis are radio anomalies detected as earthquake precursors both for MCO and CZE data. In particular, regarding the MCO data, the main result was the appearance of a very clear anomaly during May-August 1998, at daytime and at nighttime. Such an anomaly can be considered as a precursor of a seismic sequence started on August 15, 1998 with 17 earthquakes (M=2.2-4.6) on the Reatini mountains, a seismogenic zone located 30 km far from the AS receiver along the path MCO-AS. As concerns with the CZE data, the first result was obtained from the summer daytime data and it was the appearance of a very clear anomaly during August-September 1997, that can be considered a precursor of the two earthquakes with magnitude M=5.6 and M=5.9 that occurred on September 26 in the Umbria-Marche region (Central Italy). The second result was the appearance of an anomaly during February-March 1998, at daytime and at nighttime, that can be related to the preparatory phase of the strong (M=5.1-6.0) Slovenia seismic sequence that occurred in a zone lying in the middle of the CZE-AS path.

Highlights

Research into the interaction between seismic activity and disturbances in radiobroadcasts has been carried out for many years.Mainly, pre-seismic disturbances in radio waves that lie in the VLF (3-30 kHz) frequency band have been presented (Hayakawa and Sato, 1994; Hayakawa et al, 1996, 2002; Molchanov and Hayakawa, 1998)
Molchanov et al (2006) have presented possible seismic disturbances in VLF radio signals radiated by powerful transmitters located on the ground but recorded on board of the DEMETER satellite
An overview on preseismic anomalies in LF radio signals revealed in Italy by wavelet analysis moving the theoretical value of the corresponding ground wave from the experimental values of the electric field strength

Summary

Introduction

Research into the interaction between seismic activity and disturbances in radiobroadcasts has been carried out for many years. As for the ground wave, the propagation of this wave over a smooth, homogeneous, curved Earth, with exponentially decreasing refractive index (Rotheram, 1981a,b) was considered; for the sky wave, using the wave hop model (Knight, 1973; CCIR, 1990b), the sky wave signal was supposed as a ray starting from the transmitter and reflected, with one or more hops, by the lower ionosphere and by the ground Both the distances transmitter-receiver (MCO-AS and CZE-AS) are consistent with only one hop, whose reflection point on the ionosphere is in the middle of the radio path. An overview on preseismic anomalies in LF radio signals revealed in Italy by wavelet analysis moving the theoretical value of the corresponding ground wave from the experimental values of the electric field strength. It must be noted that none of the previous anomalies ever appears in either the MCO or CZE radio signals

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