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

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

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 data,
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.

Keywords


LF radio-waves;wavelet;seismicity;precursors

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References


DOI: https://doi.org/10.4401/ag-4445
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Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia - ISSN: 2037-416X