Surface motion modeling for the southeastern Carpathians: Processing and analysis of GPS observation data from the Vrancea seismic region in Romania

Abstract

The SUBDUCT (Surface Behavior and Dynamical Units of the Southeast Carpathians Tectonics) research program, in which the TU Delft participates, aims to model the surface kinematics of a 350 x 350 km wide area around the Vrancea seismic region in Romania by means of GPS observations. The goal of the project is to relate surface motions to the active crust-lithosphere dynamics of the southeast Carpathians. The main objective is to model the surface expressions of the subducted slab at 70 to 200 km depth, which is the common origin of earthquakes in the Vrancea region. Since 1995 GPS field campaigns have been performed by various research groups, and since 2002 in the framework of the subduct research program that increased the number of episodical observed sites to more than 50 and maintains 7 continuously observing permanent stations in the region. This master thesis focusses on the precise processing with the JPL GIPSY software of the GPS data from permanent and campaign stations in Romania from the years 2004 to 2006 and the combination of these newly processed solutions with previous obtained results from the period 1995 to 2003. From the total set of available solutions linear site velocities have been estimated and a complete velocity field for the entire observed region has been produced for the horizontal surface motions as well as the vertical motions. The GPS data showed to be of high quality, resulting in daily repeatabilities for campaign and permanent stations in the order of 1-2 mm for the north and east and 3-7 mm for the vertical position component. However due to the use of different antennas in subsequent observation considerable vertical position offsets were introduced for all campaign stations, which limit the reliability of the constructed vertical velocities. The most reliable estimated horizontal velocities are for the region in the order of 1-2 mm/yr with respect to the stable Eurasian plate, indicating only small relative motions in Romania. The 95% confidence limit for the sites with the longest observation history is around 0.5-2 mm/yr. The total figure of the combined horizontal site velocities shows for most areas stable and regional uniform motions. Even though the vertical site velocities are unreliable in quantitative terms, the complete vertical velocity field shows in a qualitative sense nonetheless uniform subduction and uplifting zones. Most notably is the uniformly uplifting zone north of the Trotus fauls and the subsidence in the Moesian Platform and Transilvanian Basin. After previous preliminary DEOS publications, this thesis presents a first reliable qualitative vertical velocity field of the region that can be used for geophysical interpretation.Aerospace Engineerin