Fault motion reversals predating the M-w 6.3 2009 L'Aquila earthquake: insights from synthetic aperture radar data

The millimetre accuracy of Synthetic Aperture Radar (SAR) measurements and related multi-temporal data analyses provide fundamental information on surface displacements caused by strong earthquakes. The multi-temporal analysis of SAR interferometry data allows for the geometry, kinematics and temporal behaviour of earthquake-generating faults to be better constrained, and is being acknowledged as a promising technique in the field of earthquake precursors. We used SAR data obtained by multi-temporal interferometric techniques such as Permanent Scatterers (PS) interferometry for the investigation of pre- to post-seismic ground displacements in the region struck by the M-w 6.3, 2009 L'Aquila earthquake. We analysed Europen Remote Sensing (ERS) and Envisat PS-datasets from ascending and descending orbits, and COSMO-SkyMed PS-datasets from descending orbit, collectively covering a> 20 year long time span. On a yearly scale, a reversal of motions that affected the hanging-wall and footwall blocks of the earthquake-generating fault is detected. In particular, the hanging-wall block is characterized by pre-seismic uplift - which we document as being independent of any hydrological control - and eastward horizontal motion for about six years, followed by subsidence and westward motion (starting six to eight months prior to the earthquake). We suggest that such a ground displacement pattern may represent an earthquake precursor signal.