Abstract
We measured ground displacements before and after the 2009 L’Aquila earthquake using multi-temporal InSAR techniques to identify seismic precursor signals. We estimated the ground deformation and its temporal evolution by exploiting a large dataset of SAR imagery that spans seventy-two months before and sixteen months after the mainshock. These satellite data show that up to 15 mm of subsidence occurred beginning three years before the mainshock. This deformation occurred within two Quaternary basins that are located close to the epicentral area and are filled with sediments hosting multi-layer aquifers. After the earthquake, the same basins experienced up to 12 mm of uplift over approximately nine months. Before the earthquake, the rocks at depth dilated, and fractures opened. Consequently, fluids migrated into the dilated volume, thereby lowering the groundwater table in the carbonate hydrostructures and in the hydrologically connected multi-layer aquifers within the basins. This process caused the elastic consolidation of the fine-grained sediments within the basins, resulting in the detected subsidence. After the earthquake, the fractures closed, and the deep fluids were squeezed out. The pre-seismic ground displacements were then recovered because the groundwater table rose and natural recharge of the shallow multi-layer aquifers occurred, which caused the observed uplift.
Highlights
We measured ground displacements before and after the 2009 L’Aquila earthquake using multitemporal InSAR techniques to identify seismic precursor signals
We investigated the seismic cycle associated with the earthquake by applying advanced InSAR techniques to SAR datasets from various satellite missions (RADARSAT-2, Envisat and COSMO-SkyMed) that differ in terms of their wavelengths and spatial resolutions
159 RADARSAT-2 images (75 collected along descending orbits and 84 collected along ascending orbits) that span the six years preceding the mainshock were processed with the SqueeSARTM software package[10], and 38 Envisat images collected along descending orbits that cover almost the same temporal interval as the RADARSAT-2 data were processed with the IPTA software package[11]
Summary
We measured ground displacements before and after the 2009 L’Aquila earthquake using multitemporal InSAR techniques to identify seismic precursor signals. We estimated the ground deformation and its temporal evolution by exploiting a large dataset of SAR imagery that spans seventy-two months before and sixteen months after the mainshock These satellite data show that up to 15 mm of subsidence occurred beginning three years before the mainshock. Fluids migrated into the dilated volume, thereby lowering the groundwater table in the carbonate hydrostructures and in the hydrologically connected multi-layer aquifers within the basins. This process caused the elastic consolidation of the fine-grained sediments within the basins, resulting in the detected subsidence. We present evidence of ground deformation preceding the 2009 L’Aquila earthquake We observed this deformation using multi-temporal InSAR techniques, and we propose a plausible causative mechanism. 35 COSMO-SkyMed images that were collected along ascending orbits and cover the 16 months following the earthquake were processed using the Persistent Scatterer Pair (PSP) technique[12]
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