The Stress Field in the Northern Apulia (Southern Italy), as Deduced from Microearthquake Focal Mechanisms: New Insight from Local Seismic Monitoring

Abstract

The historical seismicity catalogs report that the Gargano area (Apulia region, southern Italy) has been site of medium to high magnitude earthquakes. Instrumental seismicity suffers of the poor coverage of the seismic stations of the RSN (National Seismic Network). To improve the seismological monitoring of the area, in 2013 the OTRIONS seismic network (OSN), managed by the University of Bari - Italy, in cooperation with INGV (National Institute of Geophysics and Volcanology), was installed. In this study, focal mechanisms of single and composite events have been computed using 118 micro-earthquakes occurred in this area. We subdivided the dataset into subsets according to their location and depth, distinguishing between the Promontory zone and the Apulian foredeep. High quality focal mechanisms and low-misfit stress tensor inversion were obtained for three groups of events. To better constrain the stress tensor we included also focal mechanism solutions obtained in previous studies. In the southwestern Apulian foredeep zone, a normal fault kinematics is inferred, normal to the Apennine stress direction; in the Promontory zone, the fault kinematics indicate inverse fault mechanisms striking in NE-SW direction. Differently from previous analyses, the stress orientations inferred in this study agree with those inferred in the World Stress Map.