Foreland seismicity associated to strike-slip faulting (SE Sicily, Italy): seismotectonic implications and seismic hazard assessment

Abstract

Between February 6 and 12, 2016, an earthquake sequence affected the western sector of the Hyblean foreland domain in SE Sicily (Italy), a region characterized by several disastrous events, as the seismic history describes, of which little is still known about the seismogenic sources. Despite the low magnitude of most events (MLmax 4.3), the sequence represents one of the largest episodes of seismic strain release in the area over the last 30 years since the December 13, 1990 earthquake (ML = 5.4). Accurate seismic phase arrival times related to the seismic sequence were obtained by using a wave-correlation method which enabled a significant improvement in precision of earthquake locations, allowing to detect a N-S striking rupture area about 8 km deep. The N-S trending discontinuity well matches, in the near-surface, with the observed geological structures, in rather good agreement with the computed focal solutions which evidence a roughly N-S elongated structure characterized by a left-lateral kinematics. The detailed knowledge learned on the geometry of the fault surface activated by the seismic sequence, together with the characterization of earthquake source parameters, gave important constraints for a realistic estimation of seismic ground motion throughout stochastic simulations. The modeling technique was based on the comparison between instrumental signals of the strongest event of the sequence and the associated synthetic ones. This permitted to properly define the set of input parameters for the construction of a realistic scenario for a MW 6.1 earthquake, which provides the largest contribution to the seismic hazard for the investigated area.