Analysis of the San Giuliano di Puglia (Southern Italy) active faults: an integrated approach

Abstract

The area of San Giuliano di Puglia (Southern Italy) was struck by a moderate earthquake of Mw=5.7 on October 31st, 2002. The aim of this study is to identify and better constrain the geometry of the seismogenic structures (active, outcropping and buried faults) in the area. We used an integrated analysis of geo-structural, seismic and gravimetric data. We built three thematic databases: “faults”, “earthquakes” and “gravimetric" data: 1. The fault database consists of data extracted from the available structural and geological maps: ITHACA (ITaly HAzard from CApable faults) catalogue; DISS (Database of Individual Seismogenetic Sources) database; the "Neotectonic Map of Italy" 1:500.000; the Geological Map 1:100.000, Sheets 154, 155, 162, 163; several geological studies. 2. The earthquakes database was created by merging the data from historical and instrumental Catalogues (CPTI11; ISIDE-INGV). 3. The gravimetric database was created through the Multiscale Derivative Analysis (MDA) of the Bouguer anomaly map of the area, whose maxima show the presence of density lineaments. The integration of these datasets in GIS environment, identified three possible cases of correlation between faults, earthquakes and MDA maxima: ⦁ A clear correlation between epicentral location, fault positions and MDA maxima shows the existence of active faults; ⦁ A good correlation between MDA maxima and epicentral positions, without correspondence with faults known from geological data, can suggest the presence of buried active faults; ⦁ A good correlation between faults from geological datasets and literature and MDA maxima, without correlation with earthquakes, can indicate the existence of inactive or silent faults. Previous studies show that the main shock in the area of San Giuliano di Puglia was generated by a deep and subvertical strike-slip structure E-W trending, with a right lateral focal mechanism (Galli & Molin, 2004). Nevertheless, Vezzani et al. (2009) proposed a reverse fault mechanism. Valensise et al. (2004) suggested that the 2002 events could be related to the Mattinata fault, a major active right lateral strike-slip fault cutting across the Gargano promontory, In order to better constrain the structural framework of this area, we combined faults seismic data and a multiscale approach of gravity data in GIS environment.