GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 1.2 145 Tab. 1 - Three components co-seismic displacements and relative uncertainties estimated for the GNSS stations of the UNICT network. Coordinates are WGS84 east and north, respectively. All displacement (disp) and uncertainty (unc) values are in millimeters. For all stations, the cut-off angle is 15°, the troposphere model is the Goad-Goodmar and the meteo model used is NRLMSISE. The table can be download as ASCII file on the INGVRING web page (http://ring. gm.ingv.it ). ID Station Longitudine Latitudine disp N-S disp E-W disp UP unc N-S unc E-W unc UP VTE1 FOCE_SENTIERO 13° 15’ 57,45166’’ 42° 51’ 57,04340’’ 141 312 29 15.5 16.5 44.0 VTE2 PRETARE 13° 16’ 33,20959’’ 42° 47’ 56,56780’’ 60 282 67 19.0 16.5 46.0 VTW3 QUARTUCCIOLO 13° 14’ 46,41153’’ 42° 47’ 56,57032’’ 198 26 -349 15.5 14.5 36.0 VTW4 COLLE_CURINA 13° 13’ 55,01245’’ 42° 48’ 59,62491’’ 102 288 -769 15.5 15.0 36.0 VTW5 CASTELLUCCIO_VALLE 13° 12’ 56,20423’’ 42° 49’ 54,89014’’ 353 418 -707 15.0 13.5 37.5 Fig. 2 - Schematic seismotectonic map: coloured lines indicate the sectors of the fault system along which coseismic ruptures occurred associated to the three main seismic events. S-S’ represent the trace of sections in Fig. 1 (from EMERGEO W.G., 2016, modified). Discussion and conclusion. The distribution of events occurred respectively before and after the Mw 6.5 mainshock, depict a simple shear geometry of normal fault segments characterised to the east by principal west facing normal fault and to the west by a blind antithetic fault segment. This frame concurs to adjust the ca. E-W- trending extensional deformation (Figs. 1b and 1c). The rupture width (thickness of seismogenic layer), referred to the dip dimension of the part of this antithetic fault segment that moved during the late October sequence, extends from about 6 km- depth to 2 km below sea level and it is length few kilometre (Figs. 1b and 2) (EMERGEO W.G., 2016) Thesemiquantitativedeformation analysis along a schematic west-east transect (Fig. 1c), indicates on the footwall of the blind antithetic fault segment (Fig. 1b) both horizontal and vertical differential deformation with maximum values of about 400 and 120 mm, respectively. The east margin of this deformed area intersects the upward extension of antithetic Mt Vettore fault system. We think that the blind antithetic sliding that occurred in correspondence of the Castelluccio plain released only partially the upper crustal stress, whereas in the upper part of the antithetic fault (from 2 km to the ground surface) regional stress could have been accommodated by aseismic ductile deformation along an incipient detachment within the surficial sedimentary succession. Alternatively, the deformation recorded at the surface across the antithetic fault (Fig. 1c) could be still elastic and therefore it could be released by a future event (Fig. 1c). Based on these evidence and following the stress-triggering concept (Stein et al. , 1999; Steacy et al. , 2005). In the attempt to verify this hypothesis we installed new benchmarks in strategic positions for monitoring possible pre-seismic deformation associated with the antithetic Castelluccio Fault.