Abstract
Abstract. On 6 April 2009 a strong (Mw=6.3) earthquake occurred in the Abruzzo region (central Italy). Since 1996, the intensity of CLT (f=189 kHz, Sicily, Italy), MCO (f=216 kHz, France) and CZE (f=270 kHz, Czech Republic) broadcast signals has been collected with a ten minutes sampling rate by a receiver operating in a place located about 13 km far from the epicenter. During March 2009, the old receiver was substituted with a new one able to measure, with one minute sampling rate, the intensity of five VLF signals and five LF signals radiated by transmitters located in different zones of Europe. The MCO and CZE transmitters mentioned above are included among them. From 31 March to 1 April the intensity of the MCO radio signal dropped and this drop was observed only in this signal. The possibility that the drop was connected to problems in the transmitter or in the receiver was investigated and excluded. So, the drop indicates a defocusing of the radiated signal. Since no particular meteorological situation along the path transmitter-receiver happened, the defocusing must be related to other causes, and a possibility is presented that it is a precursor of the Abruzzo earthquake.
Highlights
The Abruzzo earthquake occurred near L’Aquila city on 6 April 2009 (UTC 01:32:39) producing damages and causalities
Since no particular meteorological situation along the path transmitter-receiver happened, the defocusing must be related to other causes, and a possibility is presented that it is a precursor of the Abruzzo earthquake
Dives exceeding 30 m were unable to reveal the bottom of this pool and it is likely that this pool is linked with some aquifer of the whole basin that is one of the largest water reserves of central Italy
Summary
The Abruzzo earthquake occurred near L’Aquila city (central Italy) on 6 April 2009 (UTC 01:32:39) producing damages and causalities. The Amare cave (L’Aquila) is situated on the southern slope of the Gran Sasso mountain chain, at a distance of 13 km from the epicentre, in a North/Northwest direction. This chain is one of the largest karst areas of the Italian Apennines and it largely consists of limestone of different geologic epochs. Since 1985, in order to investigate possible earthquakes precursors, some of the authors have installed: a) electromagnetic and acoustic equipments (Bella et al, 1989) near the bottom of the cave, b) a level meter in the De Marchi pool, c) a receiver able to measure the intensity of three LF radio signals: CLT. The result here presented was obtained by means of this receiver
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