GLOBAL POSITIONING SYSTEM MEASUREMENTS OF PRESENT-DAY CRUSTAL MOVEMENTS IN THE ARABIA-AFRICA-EURASIA PLATE COLLISION ZONE

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 Arm enia to the Aegean coast of Turkey and north-south from the southern e dge of the Eurasian plate (Pontus block) to the northern edge of the A rabian platform. Viewed from a Eurasia-fixed reference frame, sites on the northern Arabian platform move N38 +/- 13 degrees W at 20 +/- 3 m m/yr, roughly consistent with the velocity implied by NUVEL 1A circuit closure (N23 +/- 7 degrees W at 24 +/- 2 mm/yr). The motion of Arabia appears to be transferred directly to the region of Turkey north of t he suture, However, eastern Turkey is characterized by distributed def ormation while central/western Turkey is characterized by coherent pla te motion involving westward displacement and counterclockwise rotatio n of the Anatolian plate. Internal deformation within the central part of the Anatolian plate is less than 2 mm/yr. The Anatolian plate is d ecoupled from Eurasia along the right-lateral, strike-slip North Anato lian fault (NAF). This different response in eastern and western Turke y to the collision of Arabia may result from the different boundary co nditions, the Hellenic are 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 b est fitting Euler vector for Anatolia-Eurasia motion of 29.2 +/- 0.8 d egrees N, 32.9 +/- 0.4 degrees E, 1.3 +/- 0.1 degrees/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 o f 30 +/- 2 mm/yr (i.e., assuming all relative motion is accommodated a long the NAF). Using the NUVEL 1A Euler vector for Arabia-Eurasia and the GPS Euler vector for Anatolia-Eurasia, we determine an Arabia-Anat olia Euler vector of 31 +/- 2 degrees N, 45 +/- 2 degrees E, 0.9 +/- 0 .1 degrees/m.y. and an upper bound on the East Anatolian fault slip ra te of 15 +/- 3 mm/yr. The Aegean Trough region of western Turkey devia tes significantly from coherent plate rotation. In addition to rotatin g with Anatolia, this region shows roughly N-S extension at a rate of 14 +/- 5 mm/yr. Taken together with satellite laser ranging results al ong the Hellenic are, the contemporary pattern of deformation indicate s increasing motions toward the are, suggesting that the westward disp lacement and counterclockwise rotation of Anatolia is driven both by ' 'pushing'' from the Arabian plate and by ''pulling'' or basal drag ass ociated with the foundering African plate along the Hellenic subductio n zone.