GPS evidence for northward motion of the Sinai Block: Implications for E. Mediterranean tectonics
TL;DR: In this article, an elastic block model constrained by the GPS results that is consistent with the regional tectonics and allows us to estimate slip rates for Sinai bounding faults, including the Gulf of Aqaba-southern Dead Sea fault system, is presented.
About: This article is published in Earth and Planetary Science Letters.The article was published on 2005-09-30 and is currently open access. It has received 119 citations till now. The article focuses on the topics: Strike-slip tectonics.
Summary (1 min read)
1. Introduction
- The Sinai Peninsula (Fig. 1 ) lies at the northern end of the Red Sea.
- The tectonic history of the Sinai region is intimately tied to the separation of the Arabian plate from Africa along the Red Sea rift system.
- The Red Sea rift basin was well established by early Miocene at which time rifting was concentrated along the Red Sea and its northern extension along the Gulf of Suez [7] .
- Estimates of current fault slip rates in the Gulf of Aqaba and along the DSF vary considerably (e.g., see [12] for references).
- The authors use these velocities, and the velocities of IGS-GPS stations in Israel [12] to constrain an elastic block model to test the consistency of the GPS velocities with coherent block motion and to estimate slip rates on blockbounding faults.
2. GPS velocity field
- Fig. 2 shows GPS-derived velocities in the Sinai network along with velocities from continuously recording stations in surrounding areas relative to Nubia.
- Table 1 lists the velocity estimates and standard deviations.
- With the exception of sites CATH and KENS that were measured 4 times between 1997 and 2000 (sites destroyed), velocities for Sinai survey sites were determined from 5 to 7 surveys conducted between 1996 and 2003.
- In the second step the authors use the loosely constrained estimates of station coordinates, orbits, and EOP and their covariances from each day, aggregated by survey, as quasiobservations in a Kalman filter to estimate a consistent set of coordinates and velocities.
- Before estimating velocities in the second step of their analysis, the authors examine the time series of position esti- mates to determine the appropriate weights to be applied to each group's surveys.
4. Conclusions
- Survey-mode GPS observations in and around the Sinai Peninsula, in combination with continuous GPS observations in Israel, provide evidence for coherent, northerly motion of the Sinai Block.
- On average, the survey data indicate northward motion of 1.4 F 0.8 mm/yr.
- The authors use a simple elastic block model to characterize block motion and associated slip rates on block-bounding faults.
- These models suggest a 13 km locking depth for the DSF with left-lateral slip ranging from 4.4 F 0.3 to 4.7 F 0.4 mm/yr from the southern DSF to the DSF in western Syria.
- The authors are grateful to Muawia Barazangi, Francisco Gomez, Mustapha Meghraoui, and Shimon Wdowinski for helpful reviews that improved the paper.
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Figures (5)
Fig. 3. Elastic block model for the Sinai area showing GPS residual velocities (given in Table 1) for the model described in the text. Faults are vertical and assigned locking depths of 15 km except for the Gulf of Aqaba/Dead Sea fault system that has a locking depth of 13 km, and the western Cyprus Arc that has a 308 dip down to the NE. Residuals are well within the uncertainties for the velocity determinations. Numbers show fault strike slip and fault-normal slip rates and 1-sigma formal uncertainties (fault normal component in brackets; negative for left lateral and extension). Slip rates are averages along each segment. Light modeled faults indicate segments with fault-normal shortening, and dark extension. Inset shows a plot of the local Chi*2 computed from sites close to the fault (shaded error ellipses indicate sites used to estimate fault locking depth) and estimated fault strike slip rate as a function of the locking depth for the Dead Sea fault. The best fit is for a 13 km locking depth and a strike slip rate of 4.3 mm/yr. 
Fig. 1. Topographic (SRTM30) and tectonic map of the Sinai and surrounding region. Dots show seismicity (NEIC), focal mechanisms are from Harvard CMT. Inset shows location of study area within the context of the eastern Mediterranean. DSF=Dead Sea fault, Gulf of Iske.=Gulf of Iskenderum. 
Table 2 Euler vectors relative to Eurasia and 1-sigma uncertainties estimated from this study 
Fig. 2. Simplified tectonic map of the Sinai and surrounding regions show Lines with tick-marks are normal faults, ticks on downthrown block, doubl are given in Table 1. 
Table 1 GPS velocities in an Africa (Nubia)-fixed reference frame and 1-sigma uncertainties for sites shown in Fig. 2
Citations
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Massachusetts Institute of Technology1, UNAVCO2, National Science Foundation3, Kandilli Observatory and Earthquake Research Institute4, Azerbaijan National Academy of Sciences5, King Abdulaziz City for Science and Technology6, National Technical University7, Sana'a University8, Istanbul Technical University9, Ulster University10, University of Missouri11, Lebanese American University12
TL;DR: In this article, an elastic block model was developed to constrain present-day plate motions (relative Euler vectors), regional deformation within the interplate zone, and slip rates for major faults.
Abstract: [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.
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TL;DR: The Global Strain Rate Model (GSRM v.2.1) as mentioned in this paper is a new global model of plate motions and strain rates in plate boundary zones constrained by horizontal geodetic velocities.
Abstract: We present a new global model of plate motions and strain rates in plate boundary zones constrained by horizontal geodetic velocities. This Global Strain Rate Model (GSRM v.2.1) is a vast improvement over its predecessor both in terms of amount of data input as in an increase in spatial model resolution by factor of ∼2.5 in areas with dense data coverage. We determined 6739 velocities from time series of (mostly) continuous GPS measurements; i.e., by far the largest global velocity solution to date. We transformed 15,772 velocities from 233 (mostly) published studies onto our core solution to obtain 22,511 velocities in the same reference frame. Care is taken to not use velocities from stations (or time periods) that are affected by transient phenomena; i.e., this data set consists of velocities best representing the interseismic plate velocity. About 14% of the Earth is allowed to deform in 145,086 deforming grid cells (0.25° longitude by 0.2° latitude in dimension). The remainder of the Earth's surface is modeled as rigid spherical caps representing 50 tectonic plates. For 36 plates we present new GPS-derived angular velocities. For all the plates that can be compared with the most recent geologic plate motion model, we find that the difference in angular velocity is significant. The rigid-body rotations are used as boundary conditions in the strain rate calculations. The strain rate field is modeled using the Haines and Holt method, which uses splines to obtain an self-consistent interpolated velocity gradient tensor field, from which strain rates, vorticity rates, and expected velocities are derived. We also present expected faulting orientations in areas with significant vorticity, and update the no-net rotation reference frame associated with our global velocity gradient field. Finally, we present a global map of recurrence times for Mw=7.5 characteristic earthquakes.
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TL;DR: In this article, a geodetic horizontal velocity field consistent at the scale of the Mediterranean and the surrounding Alpine belts is derived to discuss the boundary conditions around each major deforming area in the Mediterranean, to describe the main patterns of motion and deformation, to critically review the existing kinematics models and to finally point out the main unresolved kinematic questions.
365 citations
TL;DR: In this article, a set of relative plate angular velocities, called GEODVEL (for GEODesy VELocity) is presented, which is based on the estimation of the position of the Earth's center and the assignment of sites to plates.
Abstract: SUMMARY
Using space geodetic observations from four techniques (GPS, VLBI, SLR and DORIS), we simultaneously estimate the angular velocities of 11 major plates and the velocity of Earth's centre. We call this set of relative plate angular velocities GEODVEL (for GEODesy VELocity).
Plate angular velocities depend on the estimate of the velocity of Earth's centre and on the assignment of sites to plates. Most geodetic estimates of the angular velocities of the plates are determined assuming that Earth's centre is fixed in an International Terrestrial Reference Frame (ITRF), and are therefore subject to errors in the estimate of the velocity of Earth's centre. In ITRF2005 and ITRF2000, Earth's centre is the centre of mass of Earth, oceans and atmosphere (CM); the velocity of CM is estimated by SLR observation of LAGEOS's orbit. Herein we define Earth's centre to be the centre of mass of solid Earth (CE); we determine the velocity of CE by assuming that the portions of plate interiors not near the late Pleistocene ice sheets move laterally as if they were part of a rigid spherical cap. The GEODVEL estimate of the velocity of CE is likely nearer the true velocity of CM than are the ITRF2005 and ITRF2000 estimates because (1) no phenomena can sustain a significant velocity between CM and CE, (2) the plates are indeed nearly rigid (aside from vertical motion) and (3) the velocity of CM differs between ITRF2005 and ITRF2000 by an unacceptably large speed of 1.8 mm yr−1. The velocity of Earth's centre in GEODVEL lies between that of ITRF2000 and that of ITRF2005, with the distance from ITRF2005 being about twice that from ITRF2000. Because the GEODVEL estimates of uncertainties in plate angular velocities account for uncertainty in the velocity of Earth's centre, they are more realistic than prior estimates of uncertainties.
GEODVEL differs significantly from all prior global sets of relative plate angular velocities determined from space geodesy. For example, the 95 per cent confidence limits for the angular velocities of GEODVEL exclude those of REVEL (Sella et al.) for 34 of the 36 plate pairs that can be formed between any two of the nine plates with the best-constrained motion. The median angular velocity vector difference between GEODVEL and REVEL is 0.028° Myr−1, which is up to 3.1 mm yr−1 on Earth's surface. GEODVEL differs the least from the geodetic angular velocities that Altamimi et al. determine from ITRF2005. GEODVEL's 95 per cent confidence limits exclude 11 of 36 angular velocities of Altamimi et al., and the median difference is 0.015° Myr−1.
GEODVEL differs significantly from nearly all relative plate angular velocities averaged over the past few million years, including those of NUVEL-1A. The difference of GEODVEL from updated 3.2 Myr angular velocities is statistically significant for all but two of 36 angular velocities with a median difference of 0.063° Myr−1. Across spreading centres, eight have slowed down while only two have sped up. We conclude that plate angular velocities over the past few decades differ significantly from the corresponding angular velocity averaged over the past 3.2 Myr.
260 citations
TL;DR: The existence of synchronous geodynamic events from one end of the system to the other, although they do not have the same meaning, is emphasized in this article, where two of them are particularly important: the Campanian-Santonian (C-S) event corresponds to obduction and exhumation of high pressure-low-temperature metamorphic rocks around the Arabian promontory, inversion along the margins of the East Mediterranean basins, and lithosphere buckling in the Atlas system (Maghreb and adjacent Sahara platform).
Abstract: [1] Along the northern border of Africa, Pangea breakup has been diachronic. During the Jurassic, the Alpine Tethys propagated northeastward from the Atlantic to the Alps. During the Permian, the Neo-Tethys propagated westward from Oman to northwestern Arabia. Then a secondary and late branch of Neo-Tethys gave birth to the East Mediterranean basin. Finally the two oceans connected at end of Jurassic times, achieving the development of Africa northern plate boundary. By the Late Cretaceous, convergence between Africa and Eurasia led to the progressive closure of the Tethys realm. The continental collision is not completely achieved, and the different segments of the confrontation zone (Maghreb, central and East Mediterranean, Zagros, and Oman) expose different stages of the process. However, we emphasize the existence of synchronous geodynamic events from one end of the system to the other, although they do not have the same meaning. Two of them are particularly important. The Campanian-Santonian (C-S) event corresponds to (1) obduction and exhumation of high-pressure–low-temperature metamorphic rocks around the Arabian promontory, (2) inversion along the margins of the East Mediterranean basins, and (3) lithosphere buckling in the Atlas system (Maghreb) and adjacent Sahara platform. The middle-late Eocene (MLE) event corresponds to (1) the onset of collision at the northern corner of Arabia, (2) the onset of slab retreat in the Mediterranean, and (3) inversion along the margin of the East Mediterranean as well as in the Atlas. The C-S event coincides with a change in plate kinematics resulting in an abrupt increase of convergence velocity. The MLE event coincides with a period of strong coupling between the Africa and Eurasia plates and an abrupt decrease of convergence velocity. In the middle of the system, the central Mediterranean seems to escape to the effects of convergence and is the site of quite permanent extensional movements since the Triassic.
259 citations
References
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TL;DR: In this paper, the authors model the geodetically observed secular velocity field in north- western Turkey with a block model that accounts for recoverable elastic-strain ac- cumulation.
Abstract: We model the geodetically observed secular velocity field in north- western Turkey with a block model that accounts for recoverable elastic-strain ac- cumulation. The block model allows us to estimate internally consistent fault slip rates and locking depths. The northern strand of the North Anatolian fault zone (NAFZ) carries approximately four times as much right-lateral motion (24 mm/yr) as does the southern strand. In the Marmara Sea region, the data show strain accu- mulation to be highly localized. We find that a straight fault geometry with a shallow locking depth of 6-7 km fits the observed Global Positioning System velocities better than does a stepped fault geometry that follows the northern and eastern edges of the sea. This shallow locking depth suggests that the moment release associated with an earthquake on these faults should be smaller, by a factor of 2.3, than previously inferred assuming a locking depth of 15 km. Online material: an updated version of velocity-field data.
230 citations
TL;DR: In this paper, a large fan at the mouth of Wadi Dahal has been displaced by about 500 m since the bulk of the fanglomerates were deposited 77-140 kyr ago, as dated from cosmogenic isotope analysis (Be in chert) of pebbles collected on the fan surface and from the age of transgressive lacustrine sediments capping the fan.
Abstract: The Araba valley lies between the southern tip of the Dead Sea and the Gulf of Aqaba. This depression, blanketed with alluvial and lacustrine deposits, is cut along its entire length by the Dead Sea fault. In many places the fault is well defined by scarps, and evidence for left-lateral strike-slip faulting is abundant. The slip rate on the fault can be constrained from dated geomorphic features displaced by the fault. A large fan at the mouth of Wadi Dahal has been displaced by about 500 m since the bulk of the fanglomerates were deposited 77–140 kyr ago, as dated from cosmogenic isotope analysis (^(10)Be in chert) of pebbles collected on the fan surface and from the age of transgressive lacustrine sediments capping the fan. Holocene alluvial surfaces are also clearly offset. By correlation with similar surfaces along the Dead Sea lake margin, we propose a chronology for their emplacement. Taken together, our observations suggest an average slip rate over the Late Pleistocene of between 2 and 6 mm yr^(−1), with a preferred value of 4 mm yr^(−1). This slip rate is shown to be consistent with other constraints on the kinematics of the Arabian plate, assuming a rotation rate of about 0.396° Myr^(−1) around a pole at 31.1°N, 26.7°E relative to Africa.
185 citations
TL;DR: In this article, the authors defined the Sinai subplate, from a seismotectonic perspective, as a distinct component in the plate tectonics of the eastern Mediterranean region, based on the tectonic characteristics of a comprehensive listing of all ML≥ 4 recorded seismicity in the region during the 20th century.
Abstract: SUMMARY
We define the Sinai subplate, from a seismotectonic perspective, as a distinct component in the plate tectonics of the eastern Mediterranean region. This is based on the tectonic characteristics of a comprehensive listing of all ML≥ 4 recorded seismicity in the region during the 20th century, on newly calculated and recalculated fault plane mechanisms of first P-wave arrivals and on published solutions based on waveform inversion of broad-band data.
The low seismicity level and scarcity of strong events in the region required a thorough search for useful data and a careful examination of the reliability of the focal solutions. We gathered all available records of first P-wave onsets from the ISS and ISC Bulletins and the local seismic networks. Altogether, we were able to calculate 48 new focal mechanisms and 33 recalculated ones of events that occurred during the years 1940–1992. With the increasing number of teleseismic and regional broad-band stations in the later years, we added 37 solutions based on teleseismic and regional waveform inversions of events that occurred during 1977–2001.
These mechanisms enabled us to examine the seismotectonic character of the Sinai subplate. The strike and rake directions of the calculated mechanisms usually reflect the geometry and the large-scale type of deformation observed along the boundaries of the Sinai subplate—the Dead Sea Transform, the Cypriot Arc convergent zone and the Suez Rift. Nevertheless, along each of these boundaries we found anomalous solutions that attest to the complexity of the deformation processes along plate margins.
Earthquakes along the Dead Sea Transform exhibit mainly sinistral transtension and transpression, reflecting its leaky manner and local change in the transform geometry. The presence of other unexpected mechanisms near the transform, however, reflects the heterogeneous deformation it induces around.
As expected, thrust mechanisms along the Cypriot Arc mirror its convergent nature and typical curved geometry. Transtension and transpressional solutions in the eastern segment of the arc reflect the sinistral shear motion between Anatolia and Sinai there. However, shear mechanisms found between Cyprus and the Eratosthenes Seamount pose a problem regarding its collision process.
Most intriguing of all are ML≥ 4 thrust and shear solutions found in the Gulf of Suez. They are associated with predominantly normal mechanisms within a rift zone and therefore constitute a unique phenomenon, yet to be deciphered.
173 citations
TL;DR: In this paper, the ITRF2000 pole of the Sinai sub-plate is defined and rotated to the reference frame (SRF) to calculate the current relative plate motion of Sinai-Arabia and Sinai-Nubia.
Abstract: [1] A network of 11 continuous GPS stations was constructed in Israel between 1996 and 2001 to monitor current crustal movements across the Dead Sea Fault (DSF). Analysis of the GPS measurements with respect to the ITRF2000 Reference Frame yields time series of daily site positions containing both secular and seasonal variations. Horizontal secular variations (station velocities) are evaluated with respect to the main tectonic element in the region, the DSF. We use six velocity vectors west of the DSF to define the ITRF2000 pole of the Sinai sub-plate, and rotate the velocity field for all stations into the Sinai reference frame (SRF). The velocity vectors reveal that (1) relative station movements are less than 4 mm/yr; (2) the nine stations located west of the DSF show no statistically significant motion with respect to the SRF; and (3) the two stations located in the Golan Heights (KATZ and ELRO) and a station in Damascus, Syria (UDMC) show 1.7–2.8 mm/yr northward motion with respect to Sinai, indicating a left-lateral motion along the DSF. Using locked-fault models, we estimate the current slip rate across the DSF as 3.3 ± 0.4 mm/yr. If we exclude the northern sites (ELRO and UDMC), which are located adjacent to the compressional jog of Mount Hermon, our estimate increases to 3.7 ± 0.4 mm/yr. The calculated ITRF2000 Sinai, Eurasia, and Nubia poles and a published pole for Arabia allow us to calculate the current relative plate motion of Sinai-Arabia and Sinai-Nubia.
172 citations
TL;DR: This article investigated the Miocene to present-day stress fields of the Kenyan rift, the northern Red Sea, and the Gulf of Suez by integrating stratigraphically constrained fault movements, aligment of radiometrically dated dikes and volcanic vents, teleseismic earthquake focal mechanisms, and borehole breakouts in exploratory wells.
111 citations