Global Positioning System measurements of present‐day crustal movements in the Arabia‐Africa‐Eurasia plate collision zone

Abstract

We present and interpret Global Positioning System (GPS) measurements of crustal motions for the period 1988–1994 at 54 sites extending east‐west from the Caucasus mountains of southern Russia, Georgia, and Armenia to the Aegean coast of Turkey and north‐south from the southern edge of the Eurasian plate (Pontus block) to the northern edge of the Arabian platform. Viewed from a Eurasia‐fixed reference frame, sites on the northern Arabian platform move N38±13°W at 20±3 mm/yr, roughly consistent with the velocity implied by NUVEL 1A circuit closure (N23±7°W at 24±2 mm/yr). The motion of Arabia appears to be transferred directly to the region of Turkey north of the suture. However, eastern Turkey is characterized by distributed deformation while central/western Turkey is characterized by coherent plate motion involving westward displacement and counterclockwise rotation of the Anatolian plate. Internal deformation within the central part of the Anatolian plate is less than 2 mm/yr. The Anatolian plate is decoupled from Eurasia along the right‐lateral, strike‐slip North Anatolian fault (NAF). This different response in eastern and western Turkey to the collision of Arabia may result from the different boundary conditions, the Hellenic arc forming a “free” boundary to the west and the Asian continent and oceanic lithosphere of the Black and Caspian Seas forming a resistant boundary to the north and east. We derive a best fitting Euler vector for Anatolia‐Eurasia motion of 29.2±0.8°N, 32.9±0.4°, 1.3±0.1°/m.y. The mapped surface trace of the NAF corresponds well to a small circle about this pole. The new Euler vector implies an upper bound for NAF slip rate of 30±2 mm/yr (i.e., assuming all relative motion is accommodated along the NAF). Using the NUVEL 1A Euler vector for Arabia‐Eurasia and the GPS Euler vector for Anatolia‐Eurasia, we determine an Arabia‐Anatolia Euler vector of 31±2°N, 45±2°E, 0.9±0.1 °/m.y. and an upper bound on the East Anatolian fault slip rate of 15±3 mm/yr. The Aegean Trough region of western Turkey deviates significantly from coherent plate rotation. In addition to rotating with Anatolia, this region shows roughly N‐S extension at a rate of 14±5 mm/yr. Taken together with satellite laser ranging results along the Hellenic arc, the contemporary pattern of deformation indicates increasing motions toward the arc, suggesting that the westward displacement and counterclockwise rotation of Anatolia is driven both by “pushing” from the Arabian plate and by “pulling” or basal drag associated with the foundering African plate along the Hellenic subduction zone.