Dipartimento di Fisica, Università La Sapienza, Roma, Italy

In this study we show that ELF-VLF emissions, occurred during the fracturing of rocks in laboratory experiments and during rock extraction in a cave, have been recorded also before earthquakes by 3 ELF-VLF stations installed in the central Apennines. The electric field emission is composed by two types of signals which are related to the evolution of micro-fractures within the rocks. During two years of monitoring, from August 2003 to September 2005, we recorded three signals, which all have frequency band and characteristics similar to the signal recorded during the fracturing of rocks in the laboratory and during the extraction of rocks. All these signals occurred a few days before the occurrence of M ≥ 4.5 earthquakes in the surrounding region (100-300 km). May be EM precursors of the earthquakes ?

This article introduces the concept of ionospheric waves with periods from about 15 min to about 4 h as one of the acoustic-gravity wave-induced phenomena. The existence of these medium-period ionospheric waves in the various ionospheric layers is supported by the results of a data analysis which has shown remarkable characteristics in occurrence and direction of the waves with a period not longer than about 2 h. The explanation offered is based on the assumption that a unique phenomenon capable to launch acoustic-gravity waves related to such ionospheric waves is the sudden change in physical conditions of the atmosphere due to the passage of the solar terminator.

Since 1987 multichannel instrumentation has been recording electromagnetic and seismoacoustic emissions in the Amare cave (Gran Sasso í L'Aquila). Equipment detecting RMC (Principality of Monaco) longwave broadcasting (216 kHz) has been operating in the same place. Data collected during this period have pointed out two different phenomena called «quiet» and «perturbed» that characterize the normal behaviour of the cave. On 25 August 1992 an earthquake with M = 3.9 occurred in the Gran Sasso area and on 4 June 1993 an earthquake with M = 4.3 occurred in Umbria, 100 km to north of the Amare cave. Before these earthquakes, electromagnetic, seismoacoustic, and RMC data showed anomalies. Here we present the observed phenomenology and discuss the possibility that the anomalies can be considered precursors of the earthquakes.