GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 1.1 91 To estimate the volumes involved in the earthquake processes and starting from the obtained interferograms, we created 104 for the subsidenced area (Fig. 1a) and 74 profiles for the uplifted zone (Fig. 1b). Applying the Cavalieri-Simpson method, we calculated the involved volumes. The subsidence and the uplift volumes are equal to 0.067 km 3 and 0.020 km 3 , respectively. Therefore, our results highlight a mass deficit within the crustal volume involved during the earthquake. We suggest that the volume loss at the surface (i.e., the subsidence) reflects a volume loss within the crustal volume at depth. In particular, deformation processes that can promote volume loss and inelastic (i.e., permanent) deformation within a rock mass are diffusion mass transfer (i.e., pressure solution) and/or plastic deformation (i.e., mineral recrystallization, grain boundary sliding) processes. These processes develop during deformation at low strain rates (i.e., during the interseismic phase) as shown by field evidence (e.g., Gratier et al. , 2013) and laboratory simulations (e.g., Tesei et al. , 2014). However, in our case, we observe a sudden volume loss in response to a high strain rate deformation (i.e., during the earthquake nucleation). Therefore, we propose that high strain rate inelastic processes must have occurred at depth to allow such volume loss. In particular, we suggest that the sudden closure of previously open fractures at depth can account for the observed volume loss (Fig. 2). These fractures could be localized within a fractured and dilated zone located anthitetically respect to the main fault, as previously suggested by Doglioni et al. (2015) and Petricca et al. (2015) for the 2009 L’Aquila earthquake. In particular, according to the model proposed by Doglioni et al. (2015), when the stresses related to gravitational energy exceed the strength of the fractured and dilated zone the rock volume collapses slipping along the main fault and generating the earthquake. References Cheloni, D. et al. ; 2017. Geodetic model of the 2016 Central Italy earthquake sequence inferred from InSAR and GPS data. Geophys. Res. Lett., 44 , 6778-6787. Chiaraluce, L. et al. ; 2017. The 2016 Central Italy Seismic Sequence: A First Look at the Mainshocks, Aftershocks, and Source Models. Seism. Res. Lett., 88 , 757-771. Doglioni, C., Carminati, E., Petricca, P. and Riguzzi, F.; 2015. Normal fault earthquakes or graviquakes. Sci. Rep., 5 . Galadini, F. and Galli, P.; 2003. Paleoseismology of silent faults in the Central Apennines (Italy): the Mt. Vettore and Laga Mts. faults. Annals of Geophys., 46 , 815-836. Galli, P., Galadini, F. and Pantosti, D.; 2008. Twenty years of paleoseismology in Italy. Earth-Science Rev., 88 , 89-117. Gratier, J. P. et al. ; 2013. Geological control of the partitioning between seismic and aseismic sliding behaviours in active faults: Evidence from the Western Alps, France. Tectonophysics, 600 , 226-242. Lavecchia, G. et al. ; 2016. Ground deformation and source geometry of the 24 August 2016 Amatrice earthquake (Central Italy) investigated through analytical and numerical modeling of DInSAR measurements and structural- geological data. Geophys. Res. Lett., 43 . Smeraglia, L. et al. ; 2017. Field-to nano-scale evidence for weakening mechanisms along the fault of the 2016 Amatrice and Norcia earthquakes, Italy. Tectonophysics, 712 , 156-169. Tesei, T. et al. ; 2014. Heterogeneous strength and fault zone complexity of carbonate-bearing thrusts with possible implications for seismicity. Earth Plan. Sci. Lett., 408 , 307-318. Fig. 2 - Geological model of the seismic cycle (i.e., pre-seismic and coseismic periods) associated with an extensional fault. During the interseismic phase, gravitational energy is stored within a hangingwall volume confined by the main normal fault and an antithetic fractured dilated zone. When the stresses exceed the strength of the dilated zone and of the main normal fault, the hangingwall volume collapses slipping along the main fault, generating the earthquake. We assume a steady stated strain rate in the ductile lower crust and a stick–slip motion in the brittle upper crust (modified from Doglioni et al. , 2015).