GNGTS 2017 - 36° Convegno Nazionale

174 GNGTS 2017 S essione 1.2 that the thrust ramps dip at relatively low angle (<30°) (Fig. 3). The trajectory of the main active seismogenic faults has been reconstructed by combining reflection seismic and surface data: these faults are characterized by prevalent listric geometry, with dip angle of 60°-70° where they crop out (and where the coseismic ruptures were observed) and become progressively less steep at depth, as indicated by the focal mechanisms of the mainshocks and by the distribution of the aftershocks. In general, therefore, our reconstruction suggests that the seismogenic normal faults are significantly steeper than pre-existing thrusts. In our seismic sections the top of the acoustic basement is marked by reflectors located between 3.2 and 4 s (Fig. 3), corresponding to about 8.5 – 11.5 km of depths. In the region of the 6.5 mainshock, this depth also corresponds to the seismicity cutoff. The correspondence between the top basement and the thickness of the seismogenic layer was already established in adjacent areas of the central Italy extensional seismic belt (Barchi and Mirabella, 2009). The depth and thickness of the seismogenic layer is lithologically controlled, since the seismicity is confined within the sedimentary cover and does not penetrate the underlying basement. The mainshocks are located close to the bottom of the seismogenic layer, within the Triassic evaporites. A sub-horizontal cut-off of seismicity is well recognized at the top of the basement, whereas only a few and low magnitude events are able to penetrate the substrate at depths higher than 12 km. References Barchi, M. R., & Mirabella, F. (2009). The 1997-98 Umbria-Marche earthquake sequence: “ Geological” vs. “seismological” faults. Tectonophysics, 476(1–2), 170–179. https://doi.org/10.1016/j.tecto.2008.09.013 Chiaraluce, L., Di Stefano, R., Tinti, E., Scognamiglio, L., Michele, M., Casarotti, E., … Marzorati, S. (2017). The 2016 Central Italy Seismic Sequence: A First Look at the Mainshocks, Aftershocks, and Source Models. Seismological Research Letters, 88(3), 757–771. https://doi.org/10.1785/0220160221 Galli, P., Peronace, E., Bramerini, F., Castenetto, S., Naso, G., Cassone, F., & Pallone, F. (2016). The MCS intensity distribution of the devastating 24 august 2016 earthquake in central Italy (Mw 6.2). Annals of Geophysics, 59(FastTrack5). https://doi.org/10.4401/ag-7287 Lavecchia, G., Castaldo, R., de Nardis, R., De Novellis, V., Ferrarini, F., Pepe, S., … Tizzani, P. (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. Geophysical Research Letters, 43(24), 12,389-12,398. https://doi.org/10.1002/2016GL071723 Pucci, S., De Martini, P. M., Civico, R., Villani, F., Nappi, R., Ricci, T., … Pantosti, D. (2017). Coseismic ruptures of the 24 August 2016, Mw 6.0 Amatrice earthquake (central Italy). Geophysical Research Letters, 44(5), 2138– 2147. https://doi.org/10.1002/2016GL071859 Tinti, E., Scognamiglio, L., Michelini, A., & Cocco, M. (2016). Slip heterogeneity and directivity of the ML 6.0, 2016, Amatrice earthquake estimated with rapid finite-fault inversion. Geophysical Research Letters, 43(20), 10,745- 10,752. https://doi.org/10.1002/2016GL071263 Fig. 3 - Composition of three seismic profiles and its geological interpretation across the S1 section.