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Media type:
E-Article
Title:
VLF-LF radio signals collected at Bari (South Italy): a preliminary analysis on signal anomalies associated with earthquakes
Contributor:
Biagi, P. F.;
Piccolo, R.;
Castellana, L.;
Maggipinto, T.;
Ermini, A.;
Martellucci, S.;
Bellecci, C.;
Perna, G.;
Capozzi, V.;
Molchanov, O. A.;
Hayakawa, M.;
Ohta, K.
Published:
Copernicus GmbH, 2004
Published in:
Natural Hazards and Earth System Sciences, 4 (2004) 5/6, Seite 685-689
Language:
English
DOI:
10.5194/nhess-4-685-2004
ISSN:
1684-9981
Origination:
Footnote:
Description:
Abstract. At the beginning of 2002 an OmniPAL receiver was put into operation at the Department of Physics of Bari University (Southern Italy). The electric field strength of five VLF-LF signals transmitted from United Kingdom (f=16kHz), France (f=20.9kHz), Germany (f=23.4kHz), Iceland (f=37.5kHz) and Italy (f=54kHz) has been monitoring with a 5s sampling frequency. In a first step we reduced the amount of the data taking one datum each 10min (mean of the ±5min raw data) and then we smoothed these data by a running adjacent averaging over 7 days. Analysing the trends we obtained, we revealed at first in the signal from the Italian transmitter two clear intensity decreases in April 2002 and in August-September 2002. At these times we observed earthquakes with M=4.3 and M=5.6 respectively near the transmitter-receiver path and a precursory effect in the previous decreases appeared. Then, we noted that all of the five radio trends in the time interval March 2002-February 2003 are more disturbed than in other periods; in particular an evident simultaneous decrease appears in January-February 2003. We propose that these disturbances are related to general excitation of the margin between the African and European plates. In a second step we examined the terminator time (evening) changes for the Italian transmitter in July-September 2002, and we found significant deviations from the mean value at the end of August, which is supportive for some precursory ionospheric signature of earthquakes.