GNGTS 2014 - Atti del 33° Convegno Nazionale

GNGTS 2014 S essione 1.1 109 ASAR and ERS image datasets spanning from 1992 to 2010 for the inter-seismic period. The SBAS algorithm allows us to follow the temporal evolution of the deformation through displacement time-series, and to analyze its spatial distribution over the temporal span covered by the SAR acquisitions. We performed several SBAS processing runs for the SAR datasets, concatenating two or three consecutive frames acquired from the same track, where available, to obtain a wider coverage and to improve the estimation of InSAR orbital errors. It is important to notice that, at the time of writing, a couple of image datasets (the most external ones with respect to the mainshocks) have not yet been processed. Finally, we cross-validated the different ground velocity maps by comparing the results of independent processing runs in the overlapping areas. We mosaicked the retrieved mean ground velocity maps basing on the mean value of the overlapping area (not considering in this step the local subsidence areas). Then, we validated the obtained results making a comparison with the available CGPS benchmarks. To this end, we estimated and subtracted the plane minimizing the differences between CGPS (re-projected along the ascending and descending LoS, respectively) and InSAR velocities. Tab. 1 - available SAR dataset for COSMO-SkyMed image beams (Stripmap mode), ERS and Envisat sensors for both ascending and descending geometries covering almost the entire Emilia Region. Sensor Orbit Track-Frame Temporal Span N° of images N° of pairs COSMO-SkyMed Ascending 05 west 8/7/12-28/12/13 26 86 COSMO-SkyMed Ascending 05 east 9/7/12-17/11/13 22 70 COSMO-SkyMed Ascending 04 13/7/12-23/12/13 25 88 COSMO-SkyMed Ascending 03 30/5/12-14/8/13 17 48 COSMO-SkyMed Ascending 10 4/7/12-14/12/13 34 128 COSMO-SkyMed Ascending 11 28/7/12-26/12/13 39 251 COSMO-SkyMed Descending 03 20/6/12-20/12/13 25 75 COSMO-SkyMed Descending 05 6/7/12-16/12/13 25 76 ERS Descending 165-2705 30/9/92-5/6/99 36 134 ASAR Descending 166-2705 25/1/03-21/8/10 33 139 Results. Ground deformation during the interseismic and preseismic phase. The mosaicked ASAR and ERS mean velocity maps relative to the time span 1992-2010 show several clear patterns ascribable to different phenomena (Fig. 1A). We observe some strong subsidence patterns (red colours) likely due to the strong human water pumping carried out in the Po Plain; these patterns are mainly concentrated where the soft sediment thickness is greater. A relative uplift pattern with respect to the Po Plain is present along the entire Apennines front, due to the general subsidence trend of the plain. Finally we observe a rough correspondence between the growth anticline and the positive velocity values (Fig. 1B). Vice versa, negative velocity patterns correspond to the locations of the tectonic synclines Ground deformation during the postseismic phase. In the mosaicked mean velocity maps we observe similar deformation patterns for both the ascending (Fig. 2A) and the descending (Fig. 2B) data: positive values (approaching to the sensor) are present in the epicentral area, reaching about 20 mm yr -1 . Moreover, as observed for the interseismic velocities, there is a rough correspondence between the growth anticline and the positive velocity values. Vice versa, negative velocity patterns correspond to the locations of the tectonic synclines. Thus, there is a general agreement between the preseismic and postseismic deformations, albeit for the afterslip pattern located in the epicentral area, where higher values are located. Local subsidence occurs