FOCAL MECHANISMS IN THE CALABRO-PELORITAN ARC REGION

In the last two decades the use of waveforms recorded at local-to-regional distances has increased considerably. Waveform modeling has been used to estimate faulting parameters of small to moderate size earthquakes (Mancilla et al., 2002; Tan et al, 2006; Zhu et al. 2006; D’Amico et al., 2008, 2010). It also provides useful information for understanding the tectonic features of many regions mainly characterized by low to moderate seismicity, contributing to better define regional deformation. The Calabro-Peloritan Arc region is one of the areas with high seismic hazard in Italy (http://zonesismiche.mi.ingv.it; “Mappa di pericolosità sismica del territorio nazionale”). In the last thirty years, crustal seismicity has been interested only by a low-to moderate activity, with just a few events of magnitude greater than 5 [“Catalogo della Sismicita Italiana” (CSI, Working Group 2001), “Bollettino Sismico Italiano” (http://bollettinosismico.rm.ingv.it/), ISIDE (http://iside.rm.ingv.it)]. We estimated the focal mechanisms of about 40 earthquakes with local magnitudes greater than 3.0 which occurred in the Calabro-Peloritan Arc region in the 2007–2010 time period. Waveforms recorded by the broadband stations of the Italian National Seismic Network managed by the Istituto Nazionale di Geofisica e Vulcanologia (INGV) were used. We applied the Cut And Paste (CAP) method (Zhao and Helmberger, 1994; Zhu and Helmberger, 1996), that permits the determination of source depth, moment magnitude and focal mechanisms using a grid search technique. This method allows also time shifts between synthetics and observed data, in order to reduce the dependence of the solution on a defined velocity model and on earthquake location error. The capacity of CAP method to obtain high quality results for the investigated dataset has been accurately verified by comparisons with different methods and by several tests related to seismic network geometry, velocity model and earthquake location uncertainties (D’Amico et al., 2011). For the earthquakes investigated, we tried different station distributions and different velocity models. The final focal mechanisms were then robustly determined. We also compared our solutions to those available in the RCMT (Regional Centroid Moment Tensor, Pondrelli et al. 2006; http://www.bo.ingv.it/RCMT/) and TDMT (Time Domain Moment Tensor; http://earthquake.rm.ingv.it/tdmt.php; Scognamiglio et al. 2009) catalogues. The results of the present study allow the implementation of the moment tensor catalogue of the area including also earthquakes of magnitude as low as 3.0. This integration will permit to improve the knowledge of the regional and local stress field, providing useful information to better understand the seismotectonic features of the study area.