GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 1.1 67 in the central sector of the CF which corresponds with the area of maximum slip expected at surface by the inversion model (Fig. 1b). Slip distribution of the first two main events highlights a slip gap in the central-southern sector of the VBF (Fig. 1b), where seismicity concentrated after August 24. The gap was “filled” by the zone of maximum slip during the Norcia event, when the hypocenter localized just in correspondence of the MST structural barrier, in an area that remained unruptured after the August 24 and October 26 events, as clearly visible looking at the evolution of the slip distribution in time along the cross section (Fig. 1). Rupture seems to propagate firstly toward the northwest, probably overlapping with the October 26 rupture zone, then toward the southeast, up to the Castelluccio basin, where surface rupture data indicate the reactivation of already mapped several minor synthetic and antithetic planes (Fig. 1c). The slip is subsequently transferred to the south (overstep) reactivating the Cordone del Vettore fault, where the maximum surface rupture of the entire area (1 to 2 m) has been observed. In this way deformation overcame the MST barrier and propagated also in its footwall for many kilometers, probably activating part of the Laga Mts fault that ruptured on August 24. Conclusions. Our results suggest that during the August 24 and October 26 events the MST acted as a barrier delimiting the two ruptures and subsequently begun to act as a stress concentrator. Following the high stress concentration in correspondence of the barrier itself, this latter then acted as an initiator of the rupture allowing the contemporaneous multiple rupture of the VBF, CVF and probably of the LF northernmost portion during the October 30 M6.5 event. In this view, the “young” CVF cannot be really considered as an eastern splay of the VBF, but rather an “independent” fault which has started in the footwall of the MST as an attempt of linkage between the LF and VBF. This hypothesis seems to be supported by the fact that the highest throws during the two major events, both at depth (slip inversion model; Fig. 1) and on the surface (coseismic ruptures; Fig. 1), have been observed on the CVF, in agreement with the fault linkage model that provides for greater displacement to be accumulated at the linkage zone. References Aki, K.; 1979: Characterization of barriers on an earthquake fault. J. Geophys. Res., 84, B11, 6140-6148. Boatwright J. and Cocco M.; (1996: Frictional constraints on crustal faulting . J. Geophys. Res., 101, 13,895–13,909, doi:10.1029/96JB00405. Chiaraluce L., Di Stefano R., Tinti E., Scognamiglio L., Michele M., Casarotti E., Cattaneo M., De Gori P., Chiarabba C., Monachesi G., Lombardi A., Valoroso L., Latorre D. and S. Marzorati; 2017: The 2016 Central Italy Seismic Sequence: A First Look at the Mainshocks, Aftershocks, and Source Models . Seismol. ���� ������ ������ Res. Lett., 88(3), doi:10.1785/0220160221. DePolo C. M., Clark D.G., Slemmons D.B. and Ramelli A.R.; 1991: Historical surface faulting in the Basin and Range province, western North America: implications for fault segmentation . J. Struct. Geol., 13(2), 123-136. Di Domenica A., Turtù A., Satolli S. and Calamita F.; 2012: Relationships between thrusts and normal faults in curved belts: new insight in the inversion tectonics of the Central-Northern Apennines (Italy). J. Struct. Geol., 42, 104–117, doi:10.1016/j.jsg.2012.06.008. Gallovič F., Imperatori W.P. and Mai M.; 2015: Effects of three-dimensional crustal structure and smoothing constraint on earthquake slip inversions: case study of the Mw6.3 2009 L’Aquila earthquake. J. Geophys. Res., 120(1), 428–449, doi:10.1002/2014JB011650. Luzi L., Puglia R., Russo E., and ORFEUS WG5; 2016a: Engineering Strong Motion Database, version 1.0. Istituto Nazionale di Geofisica e Vulcanologia, Observatories & Research Facilities for European Seismology, doi:10.13127/ESM. Luzi L., Puglia R., Russo E., D’Amico M., Felicetta C., Pacor F., Lanzano G., Çeken U., Clinton J., Costa G., Duni L., Farzanegan E., Gueguen P., Ionescu C., Kalogeras I., Özener H., Pesaresi D., Sleeman R., Strollo A. and Zaré M.; 2016b: The Engineering Strong-Motion Database: A Platform to Access Pan-European Accelerometric Data. Seismol. ���� ������ ������ �������� ����������������������� Res. Lett., 87(4), 987–997, doi:10.1785/0220150278. Perrin C., Manighetti I., Ampuero J.-P., Cappa F. and Gaudemer Y.; 2016: Location of largest earthquake slip and fast rupture controlled by along-strike change in fault structural maturity due to fault growth . J. Geophys. Res. Solid Earth, 121, 3666–3685, doi:10.1002/2015JB012671. Pizzi A. and Galadini F.; 2009: Pre-existing cross-structures and active fault segmentation in the northern-central Apennines (Italy). Tectonophysics, 476, 304–319, doi:10.1016/j.tecto.2009.03.018.