THE PIVO-2003 EXPERIMENT: A GPS STUDY OF ISTRIA PENINSULA AND ADRIA MICROPLATE MOTION, AND ACTIVE TECTONICS IN SLOVENIA

摘要

This contribution introduces our PIVO-2003 (Periadriatic-Istria Velocity Observations) GPS (Global Positioning System) experiment, designed to measure the motion of the Adria microplate and to study active deformation in Slovenia, along the NE corner of the microplate. To measure Adria's motion, we used decade-scale episodic GPS data from seven sites in the Istria peninsula of Slovenia and Croatia, which is Adria's major aseismic onshore unit, together with continuous GPS data from two permanent GPS sites on the Po Plain. We processed all of the GPS data using GIPSY (release 2.5) software and precise satellite ephemeris and clock files. We used data from 15 permanent GPS sites to define a stable European ITRF-2000 reference frame. We formally inverted subsets of the Istria and Po Plain Europe-referenced GPS velocities for a series of trial Adria-Europe rotation poles. Our average pole locates near that of Anderson and Jackson (1987),'which was derived from the inversion of a broadly distributed, circum-Adriatic set of earthquake slip vectors; this coincidence brings into question the recent hypothesis that Adria is fragmenting into two major sub-blocks. To quantify and study active deformation in Slovenia, we used the same analysis strategy and data from 35 episodic GPS sites in Slovenia and northern Croatia and tens of permanent GPS sites located in the surrounding region. We observed a significant and sharp (few mm/yr) dextral (to transpressive) gradient in the velocity field along the Sava Fault (Periadriatic zone), suggesting that lateral extrusion in the Alps may still be active today.