GNGTS 2014 - Atti del 33° Convegno Nazionale

GNGTS 2014 S essione 1.1 55 where only background seismicity has been recorded, can be successfully used to determine the pattern of coupling of the thrust fault in the interseismic period, revealing creeping patches that could act as barriers to the propagation of large earthquakes, as well as locked asperities, which might hence help determine the possible extent of future seismic ruptures. In this study we use continuous GPS observations to document the geodetic strain accumulation along the southern front of the eastern Alps in NE Italy. In particular, we invert the geodetic surface velocities using the back-slip approach (Savage, 1983), to estimate the convergence rate and the interseismic coupling on the thrust fault bounding the eastern Alps to the south. We describe the strain accommodation in the continental convergence between Adria and Eurasia in the south-eastern Alps and discuss the contribution of aseismic deformation, the magnitude and recurrence time of large earthquakes required to balance the long-term convergence and the implications in terms of seismic hazard assessment. Historical and instrumental seismicity. From west to east (Fig. 1), along the southern front of the eastern Alps, the 1695 Asolo M e 6.5 earthquake has been associated with the Bassano- Cornuda thrust (Burrato et al. , 2008). The 1873 Bellunese M e 6.3 event and the 1936 Bosco del Cansiglio M e 6.1 event are tentatively associated with the Polcenigo-Maniago thrust (Burrato et al. , 2008). The 1976 Friuli M W 6.4 earthquake sequence is associated with the Susans-Tricesimo and Buia thrust systems (Aoudia et al. , 2000; Cheloni et al. , 2012). Location and magnitude of previous events (1348 Carinzia M e 7.0 and 1511 Slovenia M e 6.9) are more uncertain. The distribution of the past earthquakes is thus consistent with the activation of the shallow portions of the thrust and indicates that in the last millennium not all segments of the thrust experienced ruptures. As regard the actual seismic activity recorded by the Friuli local seismic network (http:// www.crs.inogs.it) , background seismicity appears to be mostly concentrated at a depth of 5-15 Fig. 1 – Seismotectonic settings of NE Italy. The red lines represent the major mapped tectonic structures (modified from Burrato et al. (2008)). The arrows indicate the relative Adria-Eurasia plate motion (D’Agostino et al. , 2008). The ellipses represent the location of the greatest historical earthquakes (from CPTI11 catalogue), while the stars and the beach balls (from Pondrelli et al. , (2006)) show the location of the 1936 Bosco del Cansiglio earthquake ( Me 6.1) and of the 1976 Friuli earthquake sequence ( M W 6.4).