GNGTS 2016 - Atti del 35° Convegno Nazionale

126 GNGTS 2016 S essione 1.1 Fig. 1 – Epicentral distribution of the 208 best relocated events occurred between 2012-2015 in the study area. The circles diameter is proportional to the magnitude of events. Triangles reresent the seismic stations of the INGV national network running in the area. The composite seismogenic sources collected in the DISS catalogue (DISSWorking Group, 2015) are also shown (green boxes). The two seismic swarms occurred in December 2014 and in July 2015 are highlighted (orange circles). The relocated events, with magnitude M L ≤3, clearly show an epicentral distribution aligned along the axis of the Apennine fold-and-thrust belt, with hypocentral depth ranging from 5 to 25 km. A prevalence of oblique-slip kinematics is observed for isolated events. The December 2014 swarm (M L <3), with hypocenters located between 9 and 14 km in depth, is characterized by normal dip-slip kinematics. The July 2015 swarm (M L <3.5) occurred at depth between 19 and 23 km and it is characterized by strike-slip kinematics. In this area of the southern Apennines, the DISS catalog proposes a complex arrangement of possible seismogenic sources (green box in Fig.1). In particular, the study area represents the connection between the NW-SE-striking peri-axial structures and the roughly E-W ones affecting the frontal-foreland sector of the Apennine (Fig.1). Notwithstanding the short time interval investigated, the hypocentral distribution of the relocated events shows an overall deepening towards N and NW in the study area. The hypocentral depths and the kinematics of almost all the focal mechanisms of isolated events, as well as those of the 2014 swarm, are compatible with the NW-SE-striking typical Apennine peri-axial structures. The hypocentral depths (about 20 km) and the kinematics of events belonging to the 2015 swarm agree with the overall dynamics of the Apennine frontal-foreland sectors. It should be noted that this last swarm is located just south of the known north-Apulia seismogenic sources responsible, among the others, for the 2002 San Giuliano earthquake (Fig.1; Ripabottoni-San Severo). The attitude of the T- and P-axes of the computed focal mechanisms agree with the large scale stress regime acting in the area. References Di Bucci, D., and Mazzoli, S. (2003). The October-November 2002 Molise seismic sequence (Southern Italy): an expression of Adria intraplate deformation. Journal of the Geological Society, London, Vol. 160, 2003, pp. 503– 506. DISS Working Group (2015). Database of Individual Seismogenic Sources (DISS), Version 3.2.0: A compilation of potential sources for earthquakes larger than M 5.5 in Italy and surrounding areas. http://diss.rm.ingv.it/diss/ , Istituto Nazionale di Geofisica e Vulcanologia; DOI:10.6092 /INGV.IT -DISS3.2.0 Milano, G., 2014. Seismological investigation of the 2013 – 2014 seismic sequence of the Matese Massif (Southern Apennines, Italy). Atti del 33° Convegno Nazionale GNGTS, Tema 1: Geodinamica, 79-84. Volume: ISBN 978- 88- 940442-1-8; Raccolta: ISBN 978-88-940442-0-1.