GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione 1.1 125 release by transient slip is estimated to be M W 5.5, significantly larger than the seismic moment release. The large geodetically derived moment compared with seismic release suggests that the majority of the slip is likely to be aseismic. Our findings indicate that crustal deformation in the Pollino gap is accommodated by infrequent moderate earthquakes accompanied by significant aseismic slip episodes that release most of the accrued strain in the interseismic period. If large earthquakes (M > 6.5) occur in the Pollino gap, their recurrence is probably increased compared to adjacent regions of the southern Apennines, explaining the absence of “large” macroseismic intensities, and providing therefore new clues about the seismic/aseismic modes of seismic moment release in this area. The 2012-2015 seismicity of the Sannio-Irpinia border region (Southern Italy) A. De Matteo 1 , B. Massa 1,2 , G. Milano 2 , L. D’Auria 2,3 1 Dipartimento di Scienze e Tecnologie, Università degli Studi del Sannio, Benevento, Italy 2 Istituto Nazionale di Geofisica e Vulcanologia, sezione di Napoli Osservatorio Vesuviano, Napoli, Italy 3 Istituto per il Rilevamento Elettromagnetico dell’Ambiente, Consiglio Nazionale delle Ricerche, Napoli, Italy The Sannio and Irpinia seismogenic regions fall in the axial-frontal sector of the Southern Apennine belt. These regions have been struck by several destructive earthquakes, as the most recent 1962 and 1980. Looking at the border between these two areas, destructive earthquakes with Io≥ IXMCS, occurred in 1456, 1702, 1732.Although the location, geometry and kinematics of the causative faults of these earthquakes are still a matter of debate, at present almost three main hypotheses of active faults related to these strong earthquakes have been proposed: the Miranda- Apice, the Pago Veiano-Montaguto and the Mirabella Eclano-Monteverde . These three structures would cross the Sannio-Irpinia seismogenic border (Fig.1; DISS Working Group, 2015). Instrumental seismicity recorded in the last decades shows a marked difference between seismic activity in the Sannio and Irpinia regions. Irpinia experiences mainly single events with magnitude M L ≤3.5 and hypocentres located in the first 14 km of depth. The corresponding focal mechanisms show a prevailing normal dip-slip kinematics with NW-SE-striking planes. Conversely, the Sannio region is characterized by the occurrence of moderate (M L ≤5.0) and low magnitude seismic sequences and swarms (M L ≤4.0) with hypocentres deeper than 14 km. The focal mechanisms of single events occurring in this region match those recognized in Irpinia, but events related to two low magnitude seismic sequences showed kinematics compatible with a local NNE-SSW extension (e.g. Milano 2014 and references therein). In the north-easternmost sector of Sannio region deeper strike-slip kinematics can be also recognized (e.g. 2002 San Giuliano earthquake; Di Bucci and Mazzoli, 2002). Despite these significant differences between the two regions the transition between these seismic styles has never been deeply investigated. In order to try to characterize the seismicity of the Sannio-Irpinia border, we analyzed the present-day seismicity recorded by the Italian National Seismic Network of the INGV. In detail, the analysis is mainly devoted to a short time interval across 2012-2015 years, due to the occurrence of two low- energy seismic swarms. In order to obtain accurate hypocentral distributions and reliable fault plane solutions we collected the waveforms of all seismic events occurred in the study area to perform a re-picking of P- and S- phases and obtaining a reliable hypocentral location. The re-picking also allows to collect P-wave dataset to compute fault plane solutions.