GPS constraints on Africa (Nubia) and Arabia plate motions

Abstract

We use continuously recording GPS (CGPS) and survey-mode GPS (SGPS) observations to determine Euler vectors for relative motion of the African (Nubian), Arabian and Eurasian plates. We present a well-constrained Eurasia–Nubia Euler vector derived from 23 IGS sites in Europe and four CGPS and three SGPS sites on the Nubian Plate (−0.95 ± 4.8°N, −21.8 ± 4.3°E, 0.06 ± 0.005° Myr−1). We see no significant (>1 mm yr−1) internal deformation of the Nubian Plate. The GPS Nubian–Eurasian Euler vector differs significantly from NUVEL-1A (21.0 ± 4.2°N, −20.6 ± 0.6°E, 0.12 ± 0.015° Myr−1), implying more westward motion of Africa relative to Eurasia and slower convergence in the eastern Mediterranean. The Arabia–Eurasia and Arabia–Nubia GPS Euler vectors are less well determined, based on only one CGPS and three SGPS sites on the Arabian Plate. The preliminary Arabia–Eurasia and Arabia–Nubia Euler vectors are 27.4 ± 1.0°N, 18.4 ± 2.5°E, 0.40 ± 0.04° Myr−1, and 30.5 ± 1.0°N, 25.7 ± 2.3°E, 0.37 ± 0.04° Myr−1, respectively. The GPS Arabia–Nubia Euler vector differs significantly from NUVEL-1A (24.1 ± 1.7°N, 24.0 ± 3.5°E, 0.40 ± 0.05° Myr−1), but is statistically consistent at the 95 per cent confidence level with the revised Euler vector reported by Chu & Gordon based on a re-evaluation of magnetic anomalies in the Red Sea (31.5 ± 1.2°N, 23.0 ± 2.7°E, 0.40 ± 0.05° Myr−1). The motion implied in the Gulf of Aqaba and on the Dead Sea fault (DSF) by the new GPS Nubia–Arabia Euler vector (i.e. ignoring possible Sinai block motion and possible internal plate deformation) grades from pure left lateral strike-slip in the Gulf and on the southern DSF with increasing compression on the central and northern DSF with relative motion increasing from 5.6 to 7.5 mm yr−1 (±1 mm yr−1) from south to north. Along the northern DSF (i.e. north of the Lebanon restraining bend) motion is partitioned between 6 ± 1 mm yr−1 left-lateral motion parallel to the fault trace and 4 ± 1 mm yr−1 fault-normal compression. Relative motions on other plate boundaries (including the Anatolian and Aegean microplates) derived from the GPS Euler vectors agree qualitatively with the sense of motion indicated by focal mechanisms for large crustal earthquakes (M > 6). Where data are available on fault-slip rates on plate bounding faults (North Anatolian fault, East Anatolian fault, Dead Sea fault, Red Sea rift), they are generally lower than, but not significantly different from, the full plate motion estimates suggesting that the majority of relative plate motion is accommodated on these structures.