A seismic swarm as a dynamic ergodic stochastic process: a case study of the L’Aquila’s earthquake in 2009

The lethal earthquake of 6 April 2009 in L’Aquila, Central Italy, re-opened the discussion about the earthquake prediction due to the several precursory phenomena described in association to the event. One of the most important precursors that preceded L’Aquila main-shock was the foreshock activity. Papadopoulos et al. (NHESS, 2010) reported that a foreshock activity was there in the last months before the main-shock but the foreshock signal became very strong in the last 10 days with drastic changes in space time-size domains of local seismicity. The importance of shortterm foreshocks for the prediction of the main-shock was noted since the 1960’s. However, foreshocks appear to precede only some main shocks and not others, while there are also foreshocks too small to detect by routine seismic analysis. In this context, the aim of the paper is to analyse the phenomenon of swarm as a dynamic ergodic stochastic process with particular reference to mean time of transition of a certain class of earthquake swarms (belonging to a certain state) to other classes of varying intensity. This kind of analysis can be referred to some indicators such as the mean first passage time and the mean time to return with their respective probabilities, that constitute an important interpretive tool in forecasting.