GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 1.1 95 deformation was identified by different geodetic methods (Cirella et al. , 2009; Walters et al. , 2009), with SAR analysis constraining the April 6 th 2009 main shock source properties, and pointing to the activation of a NW-SE trending, SW dipping normal fault (the Paganica fault; Atzori et al. , 2009). SAR investigations point to subsidence since a few months before the main shock (Luo et al. , 2014; Moro et al. , 2017), while only negligible pre-event cumulative displacement has been detected to date on longer time windows through both SAR data analysis and other geodetic methods (Amoruso and Crescentini, 2010; Lanari et al. , 2010; Liu et al. , 2010). With the aim of outlining a comprehensive framework of the pre-seismic behaviour of the L’Aquila region, we have investigated, through the multi-temporal PSInSAR technique, an around 20 years long time span predating the Mw 6.3 2009 L’Aquila main shock. Materials and methods. Deformations are detectable as phase variations of the electromagnetic signal, through a multitemporal acquisition of SAR images. From the methodological point of view, in studies and research differential interferometry is applied in terms of stacking of interferograms using SBAS (Small Baseline Subset) and PS (Permanent Scatterer) techniques. In our work, we have used the PS-InSAR technique. From the interferometric PST-A database, we analysed ERS (1991 - 2001) and ENVISAT (2003 - 2010) datasets. For the ENVISAT dataset, the time span of best fitting of both ascending and descending orbits images is from January 2004 to June 2010. We have selected 24 pairs- images (24 satellite survey days) that cover an around 1500 km 2 wide region spanning across the epicentre of the 2009 L’Aquila earthquake. Single images or short period (up to a few months) without data-pairs images were not analysed. Using trigonometric relationships, from the two-point shape file (ascending and descending), we have obtained single raster images of the total vertical and horizontal displacement/ deformation (Up-Down/West-East; Lanari et al. , 2010). Results. The PS-InSAR multitemporal analysis that we have performed in a wide region spanning over the 2009 L’Aquila earthquake epicentre has allowed the detection of vertical component ground deformation predating the Mw 6.3 main shock. In particular, the analysis has shown that an about 450 km 2 wide area bounded to the NE by the Paganica fault, has recorded pre-seismic displacement starting from about three years prior to the April 6, 2009 earthquake (Fig. 1). Fig. 1 - IDW raster interpolation between PS-InSAR, descendent and ascendent, displacement values in the L’Aquila earthquake region. Left: uplift, in the 2005/05 - 2008/09 time span. Right: subsidence in the 2008/09 - 2009/02 time span.