Geological effects of the 2009 L’Aquila earthquake detected by COSMO-SkyMed high resolution interferometry

We investigated the surface effects of the April 6th, 2009, L’Aquila earthquake (Mw 6.3). The earthquake affected a large area in Central Italy causing strong damage to cities and villages in the epicentral region. The main goal of this work is the detection and characterization of the geological effects, such as Deep-seated Gravitational Slope Deformation (DGSD), which are gravity-driven ground movements occurring on large (1-5 km length, 100-500 m depth and width) rock volumes. To this aim we exploited the capabilities of the new High Resolution COSMO-SkyMed SAR2000 instrument, using the Differential SAR Interferometry (DInSAR) technique. We used a right ascending, Stripmap mode (35° incidence angle), coseimic image pair (April 4 - April 12) to measure the surface displacement. . We removed the topographic phase contribution using a detailed DEM at 5-m resolution . Local areas showing fringe complexities not directly attributed to the main tectonic pattern have been detected. By means of a geomorphological and geological analysis we interpreted such fringe patterns as due to ground displacement occurred along two different DGSD, one close to Roio Piano village, and the other North of the Barisciano village. The first DGSD is a sackung induced by the particular structural setting (down dip strata) and the high relief energy, whilst the second one appears to be a lateral spread of carbonatic bedrock. We unwrapped the interferogram to measure the local movements, and found 4-5 cm of LOS (Line Of Sight) displacement in both areas. The DGSD movement was triggered by the earthquake ground shaking, and, although in this case it did not result in a catastrophic collapse of the rock masses, it certainly indicates the presence of an increased ground shaking hazard in these areas. The L’Aquila earthquake is the second case study where the seismic triggering of DGSD has been recognized by DInSAR. It is worth noting that a step forward in terms of scale detail has been achieved thanks to the COSMO-SkyMed spatial resolution and frequency band.