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Present-day horizontal and vertical tectonic motion of the Dinarides region, Croatia, from GPS data and tide gauge data

Despite considerable attention directed towards Circum-Adriatic tectonics in the recent years, the rate and direction of Adria microplate motion and internal microplate fragmentation remain unresolved. We analyze tide gauge data from the eastern Adriatic Sea in order to assess spatial variation in vertical tectonics. Tide gauge data are available from eight sites in Italy, Slovenia, Croatia and Montenegro with long time series (30-95 years). Correlation among tide gauge records indicates that the interannual sea level variations are common mode. We are thus able to mitigate bias in trend estimates associated with interannual variations by common-mode filtering (Wdowinski et al., 1997 ; Davis et al., 1999). We find relative vertical crustal rates (with respect to the geoid) along the coast that fluctuate between 0.7 mm/yr which may be indication of active tectonic processes. Preliminary vertical rates determined from a sparse network of continuous GPS sites (with respect to reference ellipsoid) in the region are in general agreement with the tide gauge results within uncertainties. We also analyzed campaign and continuous GPS data collected along the eastern Adriatic coast in 1994-2005 to investigate the pattern of horizontal deformation. We find that NE directed horizontal shortening across the Dinarides that varies along the coast of Croatia, revealing apparent rotations that are not well resolved by the present GPS data set, but which nevertheless provide new clues regarding the modern configuration and motion of the Adria micoplate(s). Velocity estimates for Istria are compatible with previous models for Adria microplate motion (Battaglia et al., 2004 ; Calais et al. 2003). Sites in Istria have a Northward motion as expected but sites further south along the coast (latitude 44 to 45 degrees N) have a more westward motion, up to 40 degrees off from expected North Adria poles. Motions of sites on the Island of Palagruza, Croatia, outermost Dalmatian Island, and Matera, Italy, Puglia platform, respectively, differ by less than 0.20 mm/yr in magnitude and 03 degrees azimuth, which implies that Palagruza and Puglia lie on a common southern Adria microplate. We will also discuss a new project that will involve addition of a number of new continuous GPS stations, additional GPS campaigns, and other measurements.

GPS data; tide gauge data; Adria microplate; horizontal and vertical movements

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