GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione 1.1 175 The 2013-2015 seismicity in the Mercure basin (Calabria-Lucania border, southern Italy): insights on the shallow and middle crust kinematics M. Pierro 1 , L. Ferranti 1 , G. Milano 2 1 Dipartimento di Scienze della Terra, dell’Ambiente e delle Risorse, Università Federico II, Napoli, Italy 2 Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Vesuviano, Napoli, Italy Introduction. The Mercure basin lies in the axial zone of the SouthernApennines and is part of an array of troughs formed during Quaternary extension (Fig. 1). Many of the extensional faults bordering these basins are active as demonstrated by earthquake focal mechanisms (Fig. 1), geodetic velocities (Ferranti et al. , 2014), and active fault studies (Papanikolaou and Roberts, 2007). East of the chain, strike-slip motion on mostly buried faults dominate the present- day deformation (Fig. 1), with focal depths that are deeper (15-35 km) than the extensional earthquakes in the west (Boncio et al. , 2007). Between 2010 and 2013, a seismic crisis (the Pollino sequence) affected the area southeast of the Mercure basin. The strongest event had a Ml=5.0, and earthquakes distributed between 5-10 km depth, with chiefly extensional kinematics (Totaro et al. , 2015). The authors suggested that the faults activated at depth during the sequence are located SE of the basin. These faults align with WNW-ESE striking faults that bound to the north the Mercure basin (CaF and CPST, Fig. 2). The CPST is considered to be the seismogenic source of the Mw=5.5 1998 earthquake (Brozzetti et al., 2009). After the Ml=5.0 event occurred on October 25, 2012, the seismicity in the epicentral area abruptly decreased and the sequence could be considered ended in spring 2013. In order to assess the latest background seismicity of the Mercure basin and surroundings, we analyzed the seismicity between June 2013 and December 2015, immediately following the significant slowdown of the Pollino sequence. Data and results. We utilized data recorded by the seismic stations belonging to the Italian National Seismic Network of the INGV (Fig. 2). In order to obtain reliable hypocenters distribution and fault plane solutions, we collected the waveforms of the events occurred in the area between Latitude 39.300 – 40.140 and Longitude 15.800 – 16.200 to perform a re-picking of P- and S-phases and to obtain a P-wave dataset polarity. Overall, ~250 events with 1.0=Ml=3.0 Fig. 1 – Seismotectonic regimes in southern Italy (modified from Ferranti et al. , 2014). Lower hemisphere, equal area projection of focal mechanisms compiled from recent literature and on-line catalogs for earthquakes with M > 4.5; focal mechanisms are colored according to rake. Blue squares are historical earthquakes from CPTI catalog (Rovida et al., 2016); Imax,maximum macroseismic intensity.The dashed white line represents the boundary between the Adriatic and Tyrrhenian Moho.