THE ABSOLUTE GRAVITY NETWORK IN IRAN: AN OPPORTUNITY TO ANALYSE GRAVITY CHANGES CAUSED BY PRESENT-DAY TECTONIC DEFORMATION

The present-day tectonic motions in Iran mainly result from the North-South convergence between Eurasia and Arabia with a rate of about 25 mm/year. It is expected that the compressive state applied to Alborz (southern shore of Caspian sea) leads to possibly large vertical motion along the major faults. In the frame of a cooperation program between Iran and France, absolute gravity measurements (FG5#206) as well as GPS campaigns have been conducted since 2000 and are repeated every year.Part of the measurements will be used to renew the gravimetric network of Iran (9 sites) and the repetition of 3 co-located sites (Abali near the Mosha fault, Tehran (NCC), and Chesmeh-Shour in the stable central Iran) will help in better understanding the vertical motion in Alborz. After two initial series of measurements in 2000 and 2001, some preliminary results were suggesting an uplift of the order of 1 cm/year for the Abali site. A new campaign has been done in October 2002 and we report here on new results related to the tectonics of Alborz