Distribution of Seismicity before the Larger Earthquakes in Italy in The

The Region-Time-Length (RTL) algorithm has been applied to different instrumental catalogues to detect seismic quiescence before medium-to-large earthquakes in Italy in the last two decades. RTL performances are sensitive to the choice of spatial and temporal parameters. The method for automatic parameters selection developed by Chen and Wu has been applied to 12 Italian earthquakes with magnitude greater than 5. The limits of the method in constructing maps of seismic quiescence before the earthquake are demonstrated, and a simple improvement is proposed. Then a new technique, namely RTL surv , is proposed for routine surveys of the Italian seismicity. RTL surv has been applied to all the earthquakes with magnitude greater than 4 in the Italian area in the time interval 1994-2004; 4 different sub-areas have been identified, with different characteristics in the level of recorded seismicity. One sub-area – Tyrrhenian Sea-was characterized by a too low level of recorded seismicity for the application of the method. In the other three sub-areas a seismic quiescence was detected before at least the 66% of the earthquakes with magnitude greater or equal to 4 and all the earthquakes with magnitude greater than 5.