Galvani, Alessandro

Within the aim to evaluate the present day crustal deformation of central western Mediterranean and northern Africa, a regional GPs network was planned and measured in the frame of the Tyrgeonet and Algeonet projects. We analyse GPS data collected at ten geodetic monuments located in Algeria, together with the Villafranca, Roquetes, Cagliari, Matera and Noto IGS permanent stations. This GPS network is deployed in a crucial area for the comprehension of the Western Mediterranean geodynamics, being located along the collision belt between the Eurasian and African plates. Moreover, some of the Algerian stations are located in the inner Algeria, along the Atlas deformed zone that released strong seismic events in the past, not yet studied by space based geodetic techniques. Other four stations are located in the tectonically stable of the Algerian erg. In this paper we describe the network and the data analysis of the first epoch surveys performed during june 1998.

We computed the horizontal strain rate field for a sector of tbc Central-Southern Apennines (Italy) from GPS data collected during yearly repeated campaigns performed from 1994 to 2000 on tbc GeoModAp (Geodynamic Modeling of the Apennines) geodetic network. Site velocities were obtained starting from tbc daily coordinates and covariance solutions, using a Kalman filter approach. The residual velocity field with respect to a Eurasian 6xed reference frame shows two different prevalent motion trends, NE-ward for tbc eastern sector of the network and NW-ward for tbc western one. The mean strain rate tensor, obtained from a least square inversion method, shows a signifcant extensional deformation (1.2 x 10 ' strain/yr) normal to tbc Apennine chain, in agreement with seismological and neotectonic data. On the basis of tbc network dimension, of about 250 km, this value gives a well constrained estimate of about 3.0 ± 0.2 mm/yr of the extensional velocity oriented N55E, normal to the chain axis. Our results show a transition of the strain rate field from about N-S compression in tbc Tyrrbenian sfide to about NE-SW extension toward tbc Adriatic, which depicts a more complex deformation pattern.