GNGTS 2013 - Atti del 32° Convegno Nazionale

Block modeling setting and analysis. The final geodetic interseismic velocity field provides information on both crustal blocks and microplate rotations and elastic responses of the major fault systems. The so called elastic block modeling method is a kinematic approach with which geodetic velocities are modeled considering the crust subdivided on discrete rigid and elastic blocks, bounded by faults embedded in an homogeneous and isotropic half-space (Okada, 1985). This kind of approach follows the back-slip concept (Savage, 1983), where the surface velocity field is decomposed into a rotational component of blocks and an elastic component, representing a coseismic slip-deficit on the block-bounding faults boundaries. In our analysis we use the block model formulation implemented in the Matlab code of Meade and Loveless (2009), which performs a linear inversion of geodetic data to determine rotational poles for each block and the corresponding fault slip-rates. Since this approach requires defining the blocks geometry a-priori apriori, we set the block- boundary positions and fault parameters (dip angle and locking depth, i.e. seismogenic thickness of fault) using geological (DISS working group, 2010; Lavecchia et al. , 2002) information, taking into account also information from the available instrumental seismic catalogs. The whole model consists on 16 blocks related to Alps, Dinarides and Central Apennines, in order to consider a self-consistent kinematic scenario of the northern Apennines and Adriatic region. In particular we define the AT fault segment as a ~70 km long, 15° east-dipping fault, with a locking depth of 12 km, as shown by relocated microseismicity of Chiaraluce et al. (2007) and the isobaths obtained by Mirabella et al. (2011). Moreover we define the antithetic GuF as west-dipping plane of 40° with 6 km of locking depth, as a mean of the values proposed in the literature (Lavecchia et al. , 2002; Collettini et al. , 2003; Pucci et al. , 2003). Focusing our analysis on the northern sector of the Umbria-Marche Apennines, we perform different tests to verify which of the fault boundaries proposed accommodates the tectonic Fig. 2 – A) Near-field observed GPS velocities (red arrows) with block boundaries (black lines) and dipping planes (small dashed lines); blue lines are the ATF isobaths from Mirabella et al. (2011), violet ones represent fault boxes from Lavecchia et al. (2002) and green dots are the relocated microseismicity from Chiaraluce et al. (2007); large dashed box indicates the area interested by profiles shown on B-C-D; profile elements – red dots indicate observed velocities projected on the 55°N direction, with one standard deviation error bars and gray line represents the projected mean value of modeled velocities computed on a dense grid, yellow envelope indicates the variability of the modeled velocities within the swath profile and black triangle shows emerging faults tracves; B) modeling profile considering as fault boundary only the ATF fault; C) only antithetic faults as fault boundary; D)both fault systems. 149 GNGTS 2013 S essione 1.2