GNGTS 2013 - Atti del 32° Convegno Nazionale

Modeling surface GPS velocities in the Southern and Eastern Alps by finite dislocations at crustal depths A. Caporali 1 , F. Neubauer 2 , L. Ostini 1 , G. Stangl 3 , D. Zuliani 4 1 Department of Geosciences, University of Padova, Padova, Italy 2 Department of Geography and Geology, University of Salzburg, Austria 3 Austrian Academy of Sciences and BEV, Graz, Austria 4 Istituto Nazionale di Oceanografia e Geofisica Sperimentale, Centro Ricerche Sismologiche, Udine, Italy In the Eastern and Southern Alps a complex fault geometry accommodates the northward indentation of the Adria plate, the uplift of the Tauern Window, and a lateral extrusion towards the Pannonian Basin. The northeastern edge of the Adria is associated with the seismically active Friuli (Anderson and Jackson, 1987; Bressan et al. , 1998, 2006; Schmid et al. , 2004, 2008). The compressive M w =6.5 earthquake of May 6, 1976 is the largest recorded event in Friuli. The area of the Southern and Eastern Alps is characterized by significant crustal thick- ness variations (Brückl et al. , 2007, 2010). Seismic profiles show that the Eurasian and Adriatic plates interact with a thinner Pannonian unit as a structurally separated entity (Brückl et al. , 2007, 2010). Late Oligocene-Middle Miocene indentation tectonics is considered as the prima- ry agent driving substantial lateral material transfer, or “lateral extrusion” (Ratschbacher et al. , 1991a; Neubauer et al. , 2000; Willingshofer and Cloetingh, 2003; Wölfler et al. , 2011). The indentation tectonics and resulting lateral extrusion is driven by a free boundary in the east due to subduction of a remnant land-locked basin within the present-day Carpathians (e.g., Wortel and Spakman, 2000). From the structural point of view, increasing evidence demonstrates in- version of the entire Alpine-Carpathian-Pannonian system at ca. Miocene/Pliocene boundary (ca. at 5 Myr before present, e.g., Peresson and Decker, 1997) and the sudden onset of surface uplift (e.g., Genser et al. , 2007; Hergarten et al. , 2010; Wagner et al. , 2010). Extension and relat- ed normal and transtensional faults as well as subsidence in sectors of the Eastern Alps includ- ing the Pannonian basin were replaced by E-W shortening structures and related surface uplift. Using the analytic model of finite dislocation in an elastic half space of Okada (1985) and a dense set of GPS velocities, we present in this paper a first map of slip at depth. Based on structural surface data we identify a number of rectangular faults, which approximate the largest geological structures and which have the potential to accommodate the slip required to fit the GPS data (Fig. 1). We show that the GPS velocities, of the order of a few mm/yr, are consistent Fig. 1 – Three dimensional view of the model, seen from west. The rectangular faults are white rectangles, and a thicker white line on the surface represents the intersection of the prolongation of the fault with the Earth surface. A=Austria, I=Italy, SLO=Slovenia. The grey surface on the bottom is a smoothed approximation of the Moho, to emphasize that the rectangular faults are within the crust. 158 GNGTS 2013 S essione 1.2