Present-day crustal deformation and plate kinematics in the Middle East constrained by GPS measurements in Iran and northern Oman

International audienceA network of 27 GPS sites was implemented in Iran and northern Oman to measure displacements in this part of the Alpine-Himalayan mountain belt. We present and interpret the results of two surveys performed in 1999 September and 2001 October. GPS sites in Oman show northward motion of the Arabian Plate relative to Eurasia slower than the NUVEL-1A estimates (e.g. 22 +/- 2 mm yr-1 at N8°+/- 5°E instead of 30.5 mm yr-1 at N6°E at Bahrain longitude). We define a GPS Arabia-Eurasia Euler vector of 27.9°+/- 0.5°N, 19.5°+/- 1.4°E, 0.41°+/- 0.1° Myr-1. The Arabia-Eurasia convergence is accommodated differently in eastern and western Iran. East of 58°E, most of the shortening is accommodated by the Makran subduction zone (19.5 +/- 2 mm yr-1) and less by the Kopet-Dag (6.5 +/- 2 mm yr-1). West of 58°E, the deformation is distributed in separate fold and thrust belts. At the longitude of Tehran, the Zagros and the Alborz mountain ranges accommodate 6.5 +/- 2 mm yr-1 and 8 +/- 2 mm yr-1 respectively. The right-lateral displacement along the Main Recent Fault in the northern Zagros is about 3 +/- 2 mm yr-1, smaller than what was generally expected. By contrast, large right-lateral displacement takes place in northwestern Iran (up to 8 +/- mm yr-1). The Central Iranian Block is characterized by coherent plate motion (internal deformation -1). Sites east of 61°E show very low displacements relative to Eurasia. The kinematic contrast between eastern and western Iran is accommodated by strike-slip motions along the Lut Block. To the south, the transition zone between Zagros and Makran is under transpression with right-lateral displacements of 11 +/- 2 mm yr-1

Active deformation in Zagros-Makran transition zone inferred from GPS measurements

International audienceThe Bandar Abbas-Strait of Hormuz zone is considered as a transition between the Zagros collision and the Makran oceanic subduction. We used GPS network measurements collected in 2000 and 2002 to better understand the distribution of the deformation between the collision zone and the Makran subduction. Analysing the GPS velocities, we show that transfer of the deformation is mainly accommodated along the NNW-SSE-trending reverse right-lateral Zendan-Minab-Palami (ZMP) fault system. The rate is estimated to 10 +/- 3 mm yr-1 near the faults. Assuming that the ZMP fault system transfers the motion between the Makran-Lut Block and the Arabian plate, we estimate to 15 mm yr-1 and 6 mm yr-1, respectively, the dextral strike-slip and shortening components of the long-term transpressive displacement. Our geodetic measurements suggest also a 10-15 km locking depth for the ZMP fault system. The radial velocity pattern and the orientation of compressive strain axes around the straight of Hormuz is probably the consequence of the subducting Musandam promontory. The N-S Jiroft-Sabzevaran (JS) fault system prolongates southwards the dextral shear motion of the Nayband-Gowk (NG) fault system at an apparent rate of 3.1 +/- 2.5 mm yr-1. The change from strong to weak coupling for underthrusting the Arabian plate beneath the Zagros (strong) and the Makran (weak) may explain the dextral motion along the ZMP, JS/NG and Neh-Zahedan fault systems which transfer the convergence from a broad zone in the western Iran (Zagros, Tabriz fault system, Alborz, Caucasus and Caspian sea surroundings) to Makran subduction