Velocity Field across the Carmel Fault Calculated by Extended Free Network Adjustment Constraints

The Carmel Fault is one of the major geological structures of northern Israel. It is the northwestern part of Carmel-Tirtza Fault System and a northwestern branch of the Dead Sea Fault. The Carmel Fault region is covered by a monitoring geodetic network consisting of 23 sites, which were measured four times between 1999 and 2010 by means of GPS. The site velocities can be estimated only if the datum of the network has not been changed between measurement epochs. The GPS vectors must be adjusted so that the datum will remain undisturbed throughout the measurement campaigns. Usually we assume that GPS vectors define the network datum components of orientation and scale. Fluctuations in the GPS orbits could affect the orientation and scale between monitoring campaigns and therefore, in this study, we assume that GPS vectors are not immune to changes in their datum content. An appropriate approach is takento prevent the inclusion of these components in the adjustment of a 4D network. If not, the result will be an inevitable mixture between the deformation parameters and the datum components of the GPS vectors. In this study the GPS vectors from each campaign are stripped from their datum content using the extended free network adjustment constraints. The datumless measurements are used to define the datum by preliminary coordinates and linear constraints, which remain constant for all monitoring campaigns, as well as to define the position of the network points and their velocities. Later on, the variations across the network geometry can be modeled by means of a physical model.