Analysis of two microearthquake swarms in Southeastern Sicily: evidence for active faults?

Abstract

Two microearthquake swarms occurring in Southeastern Sicily during November 1999 and January 2000 were analysed with respect to their seismotectonic features. Given the low magnitude of the events fault plane solutions for only four major events were computed, which revealed normal fault and inverse fault mechanisms. From the comparison of waveforms and the relation of P- and S-wave peak amplitudes, two families of multiplets were identified, each representing a distinct type of seismic dislocation. Composite fault plane solutions for the two families showed the same trends as for the single major events. The small number of mismatches of the composite solutions supports the hypothesis of two distinct types of seismic dislocation during the whole sequence, i.e. a normal fault mechanism along E-W striking planes and an inverse fault mechanism along NE-SW striking planes.