1 - Introduction On October 30th 2016, in Central Italy, immediately north of the epicentral area of the August 24th event a strong eartquake (Mw = 6.5) reactivated the northern sector of the Monte Vettore Fault System (MVFS). Our local geodetic network was fully affected by the new event and therefore we performed a second campaign soon after (November 11th-13th, 2016) (Fig 1 and Tab 1) (De Guidi et al., 2017 in press). The measured deformation (with 95% confidence errors) was characterised by both horizontal and vertical movements. In particular, the east benchmark VTE1 documents 312 mm of eastward horizontal displacement and 29 mm of upward motion, while the VTE2 282 mm of eastward horizontal displacement and 67 mm of upward component of motion. On the contrary, all three western benchmarks recorded westward horizontal displacements (419, 288 and 26 mm) and subsidence (707, 288 and 769 mm) for stations VTW5, VTW4 and VTW3, respectively. Similar to Wilkinson et al. (2017) and the results of the DInSAR technique (http://www.irea.cnr.it/index.php?option=com_k2&view=item&id=761:nuovi-risultati-sul-terremoto-del-30-ottobre-2016-ottenuti-dai-radar-dei-satelliti-sentinel-1), we documented ca. 730 mm of ENE-WSW lengthening on a distance of 7 km in correspondence of the northern sector of the Mt. Vettore Fault Segment, while the off-fault vertical displacement between footwall and hanging-wall blocks was 736 mm, confirming the overall consistency of the different approaches and datasets (Fig 2). ID Station Longitudine Latitudine dispN-S dispE-W dispUP uncN-S uncE-W uncUP 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 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). 2.0 - 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 (Fig 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 (Fig. 1b and 2) (EMERGEO W.G., 2016) The semi quantitative deformation analysis along a schematic west-east transect (Fig. 1 C), indicates on the footwall of the blind antithetic fault segment (Fig 1 B) 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. Figure caption Fig. 1 - Simplified seismotectonic map of central Apennines (a) and geological profile across the epicentral area (b). The location of the major event (October 30th) is from GdL INGV (2016), while the main geostructural features are modified from Pierantoni et al. (2013) and Mantovani et al. (2011). (c) Semi-quantitative analysis of west-east deformation transect obtained by DInSAR technique and GNSS measurement 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). References De Guidi G., Vecchio A., Brighenti F., Caputo R., Carnemolla F., Di Pietro A., Lupo M., Maggini M., Marchese S., Messina D., Monaco C.,Naso S. (2017); Co-seismic displacement on October 26 and 30, 2016 (Mw 5.9 and 6.5) -earthquakes in central Italy from the analysis of a local GNSS network. Natural Hazards and Earth System Sciences (NHESS) in stamp EMERGEO W.G. (2016). Coseismic effects of the 2016 Amatrice seismic sequence: first geological results. Ann. Geophysics, 59, fast track 5, 2016; doi: 10.4401/ag-7195 Mantovani E., Viti M., Babbucci D., Cenni N., Tamburelli C., Vannucchi A., Falciani F., Fianchisti G., Baglione M., D’Intinosante V. and Fabbroni P. (2011). Sismotettonica dell’Appennino Settentrionale. Implicazioni per la pericolosità sismica della Toscana. Regione Toscana, Centro stampa Giunta Regione Toscana, Firenze, pagg. 88 (http://www.rete.toscana.it/sett/pta/sismica/index.shtml). Wilkinson M. W., Ken J. W. McCaffrey, Richard R. Jones, Gerald P. Roberts, Robert E. Holdsworth, Laura C. Gregory, Richard J. Walters, Luke Wedmore, Huw Goodall & Francesco Iezzi. (2017) Near-field fault slip of the 2016 Vettore Mw 6.6 earthquake (Central Italy) measured using low-cost GNSS. Scientific Reports 7, Article number: 4612 2017. doi:10.1038/s41598-017-04917-w Pierantoni P., Deiana G. and Galdenzi S. (2013). Stratigraphic and structural features of the Sibillini mountain (Umbria-Marche- Appennines, Italy). Ital. J. Geosci. (Boll. Soc. Geol. It.) Vol.132 No.3, pp. 497-520. Steacy S., Gomberg J. and Cocco M. (2005). Introduction to special section: Stress transfer, earthquake triggering, and time-dependent seismic hazard. J. Geophys. Res. 110, B05S01. Stein R.S. (1999).The role of stress transfer in earthquake occurrence. Nature 402, 605–609.
|Titolo:||Possible unslipped segments in the M. Vettore Fault System|
DE GUIDI, GIORGIO (Corresponding)
|Data di pubblicazione:||2017|
|Appare nelle tipologie:||4.1 Contributo in Atti di convegno|