We present and interpret Global Positioning System (GPS) measurements of crustal motions for the period 1988–1997 at 189 sites extending east-west from the Caucasus mountains to the Adriatic Sea and north-south from the southern edge of the Eurasian plate to the northern edge of the African plate. Sites on the northern Arabian platform move 18±2 mm/yr at N25°±5°W relative to Eurasia, less than the NUVEL-1A circuit closure rate (25±1 mm/yr at N21°±7°W). Preliminary motion estimates (1994–1997) for stations located in Egypt on the northeastern part of Africa show northward motion at 5–6±2 mm/yr, also slower than NUVEL-IA estimates (10±1 mm/yr at N2°±4°E). Eastern Turkey is characterized by distributed deformation, while central Turkey is characterized by coherent plate motion (internal deformation of <2 mm/yr) involving westward displacement and counterclockwise rotation of the Anatolian plate. The Anatolian plate is de-coupled from Eurasia along the right-lateral, strike-slip North Anatolian fault (NAF). We derive a best fitting Euler vector for Anatolia-Eurasia motion of 30.7°± 0.8°N, 32.6°± 0.4°E, 1.2°±0.1°/Myr. The Euler vector gives an upper bound for NAF slip rate of 24±1 mm/yr. We determine a preliminary GPS Arabia-Anatolia Euler vector of 32.9°±1.2°N, 40.3°±1.1°E, 0.8°±0.2°/Myr and an upper bound on left-lateral slip on the East Anatolian fault (EAF) of 9±1 mm/yr. The central and southern Aegean is characterized by coherent motion (internal deformation of <2 mm/yr) toward the SW at 30±1 mm/yr relative to Eurasia. Stations in the SE Aegean deviate significantly from the overall motion of the southern Aegean, showing increasing velocities toward the trench and reaching 10±1 mm/yr relative to the southern Aegean as a whole.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1999JB900351

Global Positioning System constraints on plate kinematics and dynamics in the eastern Mediterranean and Caucasus

SUMMARY

10 M ≥ 6.7 earthquakes ruptured 1000 km of the North Anatolian fault (Turkey) during 1939–1992, providing an unsurpassed opportunity to study how one large shock sets up the next. We use the mapped surface slip and fault geometry to infer the transfer of stress throughout the sequence. Calculations of the change in Coulomb failure stress reveal that nine out of 10 ruptures were brought closer to failure by the preceding shocks, typically by 1–10 bar, equivalent to 3–30 years of secular stressing. We translate the calculated stress changes into earthquake probability gains using an earthquake-nucleation constitutive relation, which includes both permanent and transient effects of the sudden stress changes. The transient effects of the stress changes dominate during the mean 10 yr period between triggering and subsequent rupturing shocks in the Anatolia sequence. The stress changes result in an average three-fold gain in the net earthquake probability during the decade after each event. Stress is calculated to be high today at several isolated sites along the fault. During the next 30 years, we estimate a 15 per cent probability of a M ≥ 6.7 earthquake east of the major eastern centre of Ercinzan, and a 12 per cent probability for a large event south of the major western port city of Izmit. Such stress-based probability calculations may thus be useful to assess and update earthquake hazards elsewhere.

/pdf/progressive-failure-on-the-north-anatolian-fault-since-1939-2noeok2tym.pdf

Progressive failure on the North Anatolian fault since 1939 by earthquake stress triggering

Neotectonics of Turkey – a synthesis

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.

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

We present new evidence for the propagation processes of the North Anatolian fault Folding in the Dardanelles Straits region allows us to document the timing of the deformation preceding, and the finite displacement after, the passage of the propagating tip of the fault The accuracy of the observations is due to interplay between deformation and the sea-level changes in the Mediterranean (the well-known Messinian regression followed by the Pliocene transgression) The long-term kinematics around the Sea of Marmara pull-apart (total displacement of about 85 km over the past 5 my) is similar to the present-day kinematics deduced from space geodesy At a larger scale, westward propagation of the North Anatolian fault over nearly 2000 km in the past 10 my appears to be associated with strain recovery, suggesting that the continental lithosphere retains long-term elasticity

/pdf/westward-propagation-of-the-north-anatolian-fault-into-the-3kzdtyv4hg.pdf

Westward propagation of the North Anatolian fault into the northern Aegean: Timing and kinematics

A dense network of 52 Global Positioning System (GPS) sites is used to determine the velocity field and strain rate pattern at the western end of the North Anatolian Fault Zone (NAFZ) in the Marmara Sea region, NW Anatolia. Based on four GPS campaigns carried out biannually between 1990 and 1996, the detailed kinematic field of crustal motion is calculated. The southernmost station shows an average rate of 22±3 mm/yr oriented westward relative to Istanbul (Eurasia). This value is indicative of the dextral strike-slip motion of NW Anatolia relative to the Black Sea. The GPS velocity field reveals that the sites located on the Thrace-Black Sea block show negligible motion relative to Istanbul. The GPS-based deformation pattern of three sections crossing the westward prolongation of the NAFZ is compared with neotectonic data. Both the GPS and the neotectonic data give clear evidence that most of the deformation occurs along a relatively narrow E-W oriented zone. This belt extends from the single fault trace of the NAFZ through the Gulf of Izmit, the Marmara Sea, the Sarkoy region, and the Gulf of Saros into the North Aegean Trough (NAT). In addition, the cross sections show the increasing influence of the N-S oriented extension in the Aegean Sea region. From the comparison of the directions and rates of shear and normal strain deduced from GPS data with geologic and seismic observations we conclude that the most active zone of dextral shear follows a line along Mudurnu Valley, the northern Marmara Sea and the Saros Trough where it joins the NAT.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/97JB02563

GPS and geologic estimates of the tectonic activity in the Marmara Sea region, NW Anatolia

The strain rate field in the eastern Mediterranean region, estimated by repeated GPS measurements

Deformation in the boundary zone between the Anatolian and Eurasian plates has been determined by means of repeated Global Positioning System (GPS) measurements. Three campaigns (1990, 1992, 1994) were carried out around the Marmara Sea. The network lies within the active earthquake belt of NW Anatolia, extending from the western part of the North Anatolian Fault Zone (NAFZ) to the Aegean extensional province. Results of the dense network consisting of 52 sites clearly reveal the westward motion of Anatolia. The rates amount to 17 mm/a ±3 mm/a on average relative to Istanbul, located at the northeastern edge of the Sea of Marmara. Based on the trajectories for the displacements of the observation sites it is concluded that the Marmara Sea forms a transition zone between the Europe fixed region of Thrace/Black Sea (Eurasia) and NW Anatolia. At the western extremity of NW Anatolia the motion bends from W to WSW(247°). The strain field calculated yields an E-W oriented right-lateral strike-slip movement (average 0.12 ppm/a, maximum 0.41 ppm/a) accompanied by NE-SW extension (average −0.12 ppm/a, maximum −0.52 ppm/a) at the eastern end of the Marmara Sea and N-S extension at the Aegean shore line. Comparisons with the directions of T axes derived from 65 fault plane solutions of earthquakes show remarkable agreement.

Active crustal deformation in the Marmara Sea Region, NW Anatolia, Inferred from GPS measurements

Global Positioning System (GPS) estimates of crustal deformation in the Marmara Sea region, Northwestern Anatolia

The Central and South America (CASA) GPS project aims at monitoring crustal deformations in the complex tectonic zone of the Caribbean, Cocos, Nazca and South American plate boundaries. Since 1988 several GPS campaigns have been carried out, unfortunately not always covering the whole area simultaneously.

Christian Straub

Papers

GPS and geologic estimates of the tectonic activity in the Marmara Sea region, NW Anatolia

The strain rate field in the eastern Mediterranean region, estimated by repeated GPS measurements

Active crustal deformation in the Marmara Sea Region, NW Anatolia, Inferred from GPS measurements

Global Positioning System (GPS) estimates of crustal deformation in the Marmara Sea region, Northwestern Anatolia

Crustal Deformation along the Caribbean — South American Plate Boundary Derived From The Casa GPS Project