Earthquake focal mechanisms and stress inversion in the Irpinia Region (southern Italy)

Giuseppe Pasquale (1) , Raffaella Matteis (1) , Annalisa Romeo (2) , Rosalba Maresca (1)

1 Dipartimento di Studi Geologici ed Ambientali
2 AMRA Scarl

The goal of this study was to estimate the stress field acting in the Irpinia Region, an area of southern Italy that has been struck in the past by destructive earthquakes and that is now characterized by low to moderate seismicity. The dataset are records of 2,352 aftershocks following the last strong event: the 23 November 1980 earthquake (M 6.9). The earthquakes were recorded at seven seismic stations, on average, and have been located using a three-dimensional (3D) P-wave velocity model and a probabilistic, non-linear, global search technique. The use of a 3D velocity model yielded a more stable estimation of take-off angles, a crucial parameter for focal mechanism computation. The earthquake focal mechanisms were computed from the P-wave first-motion polarity data using the FPFIT algorithm. Fault plane solutions show mostly normal component faulting (pure normal fault and normal fault with a strike-slip component). Only some fault plane solutions show strike-slip and reverse faulting. The stress field is estimated using the method proposed by Michael (J Geophys Res 92:357–368, 1987a) by inverting selected focal mechanisms, and the results show that the Irpinia Region is subjected to a NE–SW extension with horizontal (plunge 0°, trend 230°) and subvertical (plunge 80°, trend 320°), in agreement with the results derived from other stress indicators.

Mots clés: Irpinia Region; Seismicity; Focal mechanisms; Stress inversion

Giuseppe Pasquale, Raffaella Matteis, Annalisa Romeo, Rosalba Maresca. Earthquake focal mechanisms and stress inversion in the Irpinia Region (southern Italy). Journal of Seismology, 2008, 13 (1), pp.107-124. ⟨10.1007/s10950-008-9119-x⟩. ⟨hal-00478435⟩