Focal mechanism in the Apennines

Abstract

This paper compares different source mechanism models that tit first onset amplitudes for a set of seismic events that occurred in the Apennines, Italy. We selected earthquakes of magnitude greater than 1.0 that match the criteria of appropriate instrumental coverage of the epicentral area, low localisation errors and high signal-tonoise ratio. We analysed also microearthquakes recorded by dense seismic arrays very close to the epicentral area. Three source models have been tested: a simple doublecouple (three parameters, after amplitude normalisation), a double couple associated with compensated linear vector dipole (four parameters), a double couple associated with coplanar tensile crack (four parameters). Making use of statistical criteria, we compared source behaviour of seismic events occurring in two different areas. An F-test did not allow us to discriminate among the three models in the range of the analysed magnitudes. Anyway, the resulting mechanisms show consistent patterns in terms of tectonic stress regimes, being the T axis in the anti- Apenninic direction.