GNGTS 2013 - Atti del 32° Convegno Nazionale

During the seismic sequence we detected a rapid deformation transient which likely occurred between the two events, and which could be attributed to an aseismic dislocation (perhaps triggered by the first event) occurred on the fault plane of the second event. Unfortunately this deformation event is mapped on only two images, and its temporal behaviour is not known (Pezzo et al. , 2013). In the post-seismic phase of the Emilia sequence, our results did allow to detect deformation transients in the areas of the largest shocks of the sequence, with progressively decreasing ground velocities during a period of few months. The temporal (and spatial) characteristics of these signals suggest that they are related to afterslip along the same faults activated during the sequence. The amount of total postseismic surface displacement is about 5-10% of the coseismic one. Modeling is under way to determine in which parts of the sources this afterslip was released. A methodological consideration stemming from our work is that time series InSAR is certainly able to measure small ground velocity transients, with temporal wavelengths of several days, but to this purpose an ad hoc monitoring strategy must be put in place and strictly followed. In particular, for X-band imagery as COSMO-SkyMed, a very high repeat pass frequency is required (1-4 days), and temporal acquisition gaps must be avoided, to prevent loss of coherence and signal degradation. In both the Emilia and Pollino cases the image sampling was well below these requirements and we were only able to detect the post-seismic transient signals. Finally, we stress that the search for possible preseismic ground deformation anomalies should not be abandoned based on the results of this study, but should be approached isolating test cases involving larger earthquakes than those considered here, and integrating Continuous GPS networks with a 10-km spacing, with InSAR time series with a very high sampling rate (1-4 days). Acknowledgements. The COSMO-SkyMed SAR data are copyright of ASI. We thank all public and private institutions that manage and distribute the GPS data. We thank FOGER for providing the Emilia-Romagna GNSS network, the Dept. of Earth Science of the University of Siena and the Dept. of Physics of the University of Bologna for providing data of the GPS station in Finale Emilia. A particular thanks is addressed to Dr. Paolo Riccardi (Sarmap) for his fruitful support during the SAR data processing. References Berardino, P., Fornaro, G., Lanari, R. & Sansosti, E.; 2002: A new algorithm for surface deformation monitoring based on small baseline differential SAR interferograms . IEEE Trans. Geosci. Remote Sens., 40 (11), 2375-2383. Bernard P., Boudin F., Sacks S., Linde A., Blum P.-A., Courteille C., Esnoult M.-F, Castarede H., Felekis S. and Billiris H.; 2004 : Continuous strain and tilt monitoring on the Trizonia Island, Rift of Corinth, Greece . Compt. Rend. Geosci., 336, 313-323. Bigi, G., G. Bonardi, R. Catalano, D. Cosentino, F. Lentini, M. Parotto, R. Sartori, P. Scandone and E. Turco (Eds.); 1983: Structural Model of Italy 1:500,000 . CNR Progetto Finalizzato Geodinamica. Cakir Z., A.M. Akoglu, S. Belabbes, S. Ergintav, M. Meghraoui; 2005: Creeping along the Ismetpasa section of the North Anatolian fault (Western Turkey): rate and extent from InSAR . Earth. Planet. Sci. Lett., 238, pp. 225-234 Calais E., N. d Oreye, J. Albaric, A. Deschamps, D. Delvaux, J. Deverchere, C. Ebinger, R.W. Ferdinand, F. Kervyn, A.S. Macheyeki, A. Oyen, J. Perrot, E. Saria, B. Smets, D.S. Stamps, C. Wauthier; 2008 : Aseismic strain accommodation by slow slip and dyking in a youthful continental rift.. East Africa Nature, 456. F. R. Cinti, L. Cucci, D. Pantosti, G. D’Addezio, M. Meghraoui; 1997: A major seismogenic fault in a ‘silent area’: the Castrovillari fault (southern Apennines, Italy , Geophysical Journal International, 130, 3, 595-605. Dragert, H., Wang, K. & Rogers, G.; 2004: Geodetic and seismic signatures of episodic tremor and slip in the northern Cascadia subduction zone . Earth Planets Space 56, 1143-1150 Emergeo Working Group: Alessio, G., L. Alfonsi, C. A. Brunori, P. Burrato, G. Casula, F. R. Cinti, R. Civico, L. Colini, L. Cucci, P. M. De Martini, E. Falcucci, F. Galadini, G. Gaudiosi, S. Gori, M. T. Mariucci, P. Montone, M. Moro, R. Nappi, A. Nardi, R. Nave, D. Pantosti, A. Patera, A. Pesci, G. Pezzo, M. Pignone, S. Pinzi, S. Pucci, S. Salvi, C. Tolomei, P. Vannoli, A. Venuti, and F. Villani; 2013: Coseismic geological effects associated with the Emilia earthquake sequence of May-June 2012 (Northern Italy) . Nat. Hazards Earth Syst. Sci. 13, 1-13. Furuya M., S.P. Satyabala; 2008: Slow earthquake in Afghanistan detected by InSAR . Geophys. Res. Lett., 35. 208 GNGTS 2013 S essione 1.2