Constraining primary surface rupture length along the Paganica fault (2009 L’Aquila earthquake) with geological and geodetic (DInSAR and GPS) data

Field surveys performed by different research groups after the April 6, 2009 L’Aquila earthquake (Mw 6.1; CHIARALUCE et alii, 2011) identified the occurrence of surface faulting along the Paganica normal fault, the causative seismogenic source of the event. The different researchers provided patterns of surface rupture that slightly differ as for the northern and southern portion of the Paganica fault. We here integrated coseismic geodetic data – DInSAR and GPS – with geological observations in order to discriminate what, among the different surface rupture patterns, can be considered as evidence of primary surface faulting. Our results indicated that the Mt. Stabiata-Mt. Castellano faults, to the north, and the San Demetrio fault, to the south – along to which BONCIO et alii (2010) and GALLI et alii (2010) detected ground ruptures, respectively – probably activated solely as sympathetic (sensu SleMMONS & DE POLO, 1986; DE POLO, 1994) tectonic structures during the 2009 earthquake. These observations allowed to constrain the extension of the primary surface faulting from the Collebrincioni sector to the area of San Gregorio, thus representing the northern and the southern tips of the Paganica fault, respectively. This defines a total surface rupture length of 12-13 km. Our results highlight the effectiveness of entwining geological and geodetic data to discriminate primary surface faulting from secondary fault ruptures, particularly in cases of moderate magnitude earthquakes, i.e. when modest and rather subtle surface faulting can occur. KEY WORDS: 2009 L’Aquila earthquake, primary surface faulting, sympathetic faulting, Paganica fault central Apennines.