VLF-LF radio signals collected at Bari (South Italy): a preliminary analysis on signal anomalies associated with earthquakes

• Main Authors: Biagi PF, Piccolo R, Castellana L, Ermini A, Martellucci S, Bellecci C, Perna G, Capozzi V, Molchanov OA, Hayakawa M, Ohta K., MAGGIPINTO, TOMMASO
• Other Authors: Biagi, Pf, Piccolo, R, Castellana, L, Maggipinto, Tommaso, Ermini, A, Martellucci, S, Bellecci, C, Perna, G, Capozzi, V, Molchanov, Oa, Hayakawa, M, Ohta, K.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2004
• Subjects: Iceland
• Online Access: http://hdl.handle.net/11586/87112

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=37.5 kHz) and Italy (f=54 kHz) has been monitoring with a 5 s sampling frequency. In a first step we reduced the amount of the data taking one datum each 10 min (mean of the 5 min 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.