[1] The GPS-derived velocity field (1988–2005) for the zone of interaction of the Arabian, African (Nubian, Somalian), and Eurasian plates indicates counterclockwise rotation of a broad area of the Earth's surface including the Arabian plate, adjacent parts of the Zagros and central Iran, Turkey, and the Aegean/Peloponnesus relative to Eurasia at rates in the range of 20–30 mm/yr. This relatively rapid motion occurs within the framework of the slow-moving (∼5 mm/yr relative motions) Eurasian, Nubian, and Somalian plates. The circulatory pattern of motion increases in rate toward the Hellenic trench system. We develop an elastic block model to constrain present-day plate motions (relative Euler vectors), regional deformation within the interplate zone, and slip rates for major faults. Substantial areas of continental lithosphere within the region of plate interaction show coherent motion with internal deformations below ∼1–2 mm/yr, including central and eastern Anatolia (Turkey), the southwestern Aegean/Peloponnesus, the Lesser Caucasus, and Central Iran. Geodetic slip rates for major block-bounding structures are mostly comparable to geologic rates estimated for the most recent geological period (∼3–5 Myr). We find that the convergence of Arabia with Eurasia is accommodated in large part by lateral transport within the interior part of the collision zone and lithospheric shortening along the Caucasus and Zagros mountain belts around the periphery of the collision zone. In addition, we find that the principal boundary between the westerly moving Anatolian plate and Arabia (East Anatolian fault) is presently characterized by pure left-lateral strike slip with no fault-normal convergence. This implies that “extrusion” is not presently inducing westward motion of Anatolia. On the basis of the observed kinematics, we hypothesize that deformation in the Africa-Arabia-Eurasia collision zone is driven in large part by rollback of the subducting African lithosphere beneath the Hellenic and Cyprus trenches aided by slab pull on the southeastern side of the subducting Arabian plate along the Makran subduction zone. We further suggest that the separation of Arabia from Africa is a response to plate motions induced by active subduction.

GPS constraints on continental deformation in the Africa-Arabia-Eurasia continental collision zone and implications for the dynamics of plate interactions

SUMMARY A 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 ± 2m m 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 ± 2m m yr −1 ) and less by the Kopet-Dag (6.5 ± 2m m 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 ± 2m m yr −1 and 8 ± 2m m yr −1 respectively. The right-lateral displacement along the Main Recent Fault in the northern Zagros is about 3 ± 2m m yr −1 , smaller than what was generally expected. By contrast, large rightlateral displacement takes place in northwestern Iran (up to 8 ± mm yr −1 ). The Central Iranian Block is characterized by coherent plate motion (internal deformation < 2m m yr −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 ± 2m m yr −1 .

/pdf/present-day-crustal-deformation-and-plate-kinematics-in-the-4g6yjp3ie8.pdf

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

https://www.utdallas.edu/~rjstern/egypt/PDFs/Cenozoic%20Red%20Sea/BosworthRedSeaJAES05.pdf

The Red Sea and Gulf of Aden Basins

The East African rift system

SUMMARY The Western Mediterranean displays a complex pattern of crustal deformation distributed along tectonically active belts developed in the framework of slow oblique plate convergence. We used earthquake and Global Positioning System (GPS) data to study the present-day kinematics and tectonics of the Africa-Eurasia plate boundary in this region. Crustal seismicity and focal mechanisms, analysed in terms of seismic moment release and seismic deformation, outline the geometry of major seismic belts and characterize their tectonics and kinematics. Continuous GPS data have been analysed to determine Euler vectors for the Nubian and Eurasian plates and to provide the global frame for a new Mediterranean GPS velocity field, obtained by merging continuous and campaign observations collected in the 1991‐2005 time span. GPS velocities and displacements predicted by the Nubia-Eurasia rotation pole provide estimates of the deformation accommodated across the tectonically active belts. The rather simple deformation occurring in the Atlantic region, characterized by extension about perpendicular to the Middle Atlantic and Terceira ridges and right-lateral motion along the Gloria transform fault, turns into a complex pattern of deformation, occurring along broader seismic belts, where continental lithosphere is involved. Our analysis reveals a more complex fragmentation of the plate boundary than previously proposed. The roughly E-W trending mainly compressive segments (i.e. southwestern Iberia, northern Algeria and southern Tyrrhenian), where plate convergence is largely accomodated across rather localized deformation zones, and partially transferred northward to the adjacent domains (i.e. the Algero-Balearic and Tyrrhenian basins), are interrupted by regions of more distributed deformation (i.e. the Rif-Alboran-Betics, Tunisia-Libya and eastern Sicily) or limited seismicity (i.e. the Strait of Sicily), which are characterized by less homogeneous tectonics regimes (mainly transcurrent to extensional). In correspondence of the observed breaks, tectonic structures with different orientation interfere, and we find belts with only limited deformation (i.e. the High and Middle Atlas, the Tunisian Atlas and the offshore Tunisia-Libya belt) that extends from the plate boundary into the Nubian plate, along pre-existing tectonic lineaments. Our analysis suggest that the Sicilian-Pelagian domain is moving independently from Nubia, according to the presence of a right-lateral and extensional decoupling zone corresponding to the Tunisia-Libya and Strait of Sicily deformation zone. Despite the space variability of active tectonic regimes, plate convergence still governs most of the seismotectonic and kinematic setting up to the central Aeolian region. In general, local complexities derive from pre-existing structural features, inherited from the tectonic evolution of the Mediterranean region. On the contrary, along Calabria and the Apennines the contribution of the subducted Ionian oceanic lithosphere and the occurrence of microplates (i.e. Adria) appear to substantially modify both tectonics and kinematics. Finally, GPS data across the Gibraltar Arc and the Tyrrhenian-Calabria domain support the hypothesis that slab rollback in these regions is mostly slowed down or stopped.

/pdf/kinematics-of-the-western-africa-eurasia-plate-boundary-from-22mvv5o50v.pdf

Kinematics of the Western Africa-Eurasia plate boundary from focal mechanisms and GPS data

SUMMARY 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 (> 1m m 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 (± 1m m yr −1 ) from south to north. Along the northern DSF (i.e. north of the Lebanon restraining bend) motion is partitioned between 6 ± 1m m yr −1 left-lateral motion parallel to the fault trace and 4 ± 1m m yr −1 faultnormal 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.

/pdf/gps-constraints-on-africa-nubia-and-arabia-plate-motions-h9x6u7u4wg.pdf

GPS constraints on Africa (Nubia) and Arabia plate motions

The Al Hoceima (Morocco) earthquake of 24 February 2004, analysis and interpretation of data from ENVISAT ASAR and SPOT5 validated by ground-based observations

GPS velocities and seismicity across the Betic-Rif Arc structural domains (Morocco and Iberia) provide a basis to evaluate present-day seismotectonic processes between different deformation belts. The results show asymmetric movements in the complex Alboran system accommodating the convergence between the African (Nubian) and Eurasian plates. While the Betic Mountains are attached to Iberia, moving toward the southeast with respect to Africa, the Rif is divided into three blocks with distinct displacements relative to Nubia: (1) the Tangier block moving southeastward, (2) the Central Rif block moving SSW, and (3) the Oriental Rif block undergoing clockwise rotation. GPS-derived motions decrease in rate from the Rif nappes complex to the foreland.

Present-day movements of tectonic blocks in the Betic-Rif Arc from GPS measurements 1999-2005

Active Tectonics of the western Mediterranean: GPS evidence for roll back of a delaminated subcontinental lithospheric slab beneath the Rif Mountains, Morocco.

D. Ben Sari

Papers

GPS constraints on Africa (Nubia) and Arabia plate motions

The Al Hoceima (Morocco) earthquake of 24 February 2004, analysis and interpretation of data from ENVISAT ASAR and SPOT5 validated by ground-based observations

Present-day movements of tectonic blocks in the Betic-Rif Arc from GPS measurements 1999-2005

Active Tectonics of the western Mediterranean: GPS evidence for roll back of a delaminated subcontinental lithospheric slab beneath the Rif Mountains, Morocco.

Preliminary Evidence of Active Deformation in Morocco from Repeat GPS Observations