A New Robust Algorithm for Fault-Plane Parameters Identification: the 2009 L’Aquila (Central Italy) Seismic Sequence Case

The study of the hypocenters distribution of seismic events related to fault structures is a crucial topic since it is linked to the geological features and to the dynamics of the investigated area. The hypocenter spatial distribution of earthquakes is used in a novel algorithmic method to clusterize earthquakes to accurately identify the strike and the dip parameters of the seismogenic faults. Our algorithm works as a three-dimensional scanner which explores the hypocenter’s spatial distribution. The result is a volume that contains the maximum number of earthquakes occurring within a minimum distance from a flat area corresponding to the searched fault. The algorithm randomly selects several seismic events (pivots), explores the neighbourhood of each pivot event and searches in all angular directions how many hypocenters can be included in a prefixed volume. At the end of the procedure, we obtain, as solution, a density hypocenters occurrence angular diagram and a likelihood function. The likelihood function is useful to individuate the best value of the fault thickness and to test the hypothesis of fault flatness. Our algorithm has been tested on simulated data and then successfully applied on the real case of the 2009 Mw6.1 L’Aquila (Central Italy) seismic sequence.