Global Positioning System (GPS) observations in Azerbaijan and surrounding areas of the Caucasus region are providing quantitative constraints of the geometry of active fault systems, and rates of present-day deformation. West of 48° E longitude, the Main Caucasus Trust Fault (MCT) follows the sharp change in slope along the south side of the Greater Caucasus as is well known from prior seismic, geophysical, and geologic studies. However, east of this longitude the MCT turns sharply to the south, crossing the Kura Depression and extending along the western side of the Caspian Sea (here called the West Caspian Fault; WCF). While the MCT is predominantly a thrust fault west of 48°E longitude, the WCF is a pure rightlateral, strike slip fault with a slip rate of 11 ± 1 mm/yr south of the Absheron Peninsula. We also document shortening of 4 ± 1 mm/yr along the northern side of the Greater Caucasus in Dagestan on a roughly E-W striking fault that turns to the south inland of the north Caspian shoreline. This fault configuration implies that the Baku area is at the junction of four fault systems, the MCT, the West Caspian Fault, the North Caspian Fault, and the Central Caspian Seismic Zone. The rate of convergence on the MCT decreases from east to west from 10 ± 1 mm/yr at 48° E longitude to 4 ± 1 mm/yr in northwestern Azerbaijan (~46°E longitude). In eastern Azerbaijan, there is no evidence of active shortening in the Lesser Caucasus or Kura Depression, indicating that any deformation in this area is below present velocity uncertainties (± 0.5 mm/yr). The present-day pattern of horizontal motions in aggregate suggests that the Lesser Caucasus and Kura Depression are rotating coherently (i.e., little or no internal deformation) in a counterclockwise sense about a pole located near the NE corner of the Black Sea, resulting in the observed W to E increase in the rate of convergence along the MCT. These new, quantitative constraints on fault activity provide an improved physical basis for estimating earthquake hazards in Azerbaijan.

Some new data on modern tectonic deformation and active faulting in azerbaijan (according to global positioning system measurements)

A sequence of earthquakes took place in June 2004 approximately 60 km southeast of Tabuk, Saudi Arabia. The first felt event (MW = 3.9) occurred on June 9 and caused minor damage in the epicentral area according to the National Earthquake Information Center and the local reports. Another moderate size event occurred on June 22 (MW = 5.1) and was followed by a few felt aftershocks without any reported damage. This earthquake sequence caused considerable alarm at Tabuk and highlights the fact that damaging earthquakes can occur in this region away from the major plate boundary in the Red Sea. Being the largest well-recorded event in the area for which the digital and broadband records from Saudi Arabia, Egypt, Israel, Jordan, Turkey, Cyprus, and Kuwait are available, it provides an excellent opportunity to study the tectonic process and present day stress field acting on this area. The digital records from these regional networks were used to relocate the largest three events of this sequence. Focal mechanisms were obtained from full waveform inversion and indicate normal faulting mechanisms with two nodal planes oriented NW–SE in parallel to the faults bounding the Tabuk graben and the Red Sea rift axis. These events originated at shallow focal depths of 4–5 km, possibly contributing to the widely felt ground motions. These events offer a unique opportunity to study the active tectonics of the region as well as inform future studies of seismic hazard in northwestern Saudi Arabia, the Gulf of Aqaba, and eastern Egypt.

Source mechanisms of the June 2004 Tabuk earthquake sequence, Eastern Red Sea margin, Kingdom of Saudi Arabia

The present work deals with the tectonic position of the Sinai Peninsula based on the interpretation of magnetic data. A high-resolution magnetic survey was undertaken, combined with aeromagnetic data, GPS and seismic stress-tension analysis. The magnetic data was interpreted using the analytical signal, horizontal gradient, Euler and Werner deconvolutions and 2.5 dimensional magnetic modelling methods. The seismological focal mechanism and stress-tension forces have also been evaluated. We conclude that the structural trend N35??N45? west reflects the most predominant tectonic force in the southern part of the Sinai Peninsula, with a secondary N45??N65? east tectonic trend. Interestingly, this situation is reversed in the northern part of the peninsula. The depth of the basement rocks ranges from zero at the southern end to more than 4 km below sea level at the northern end of the studied area. Furthermore, we found that the depth of the basement rocks increases from east to west, which is consistent with available well log data. This reflects a source of stress situated in the south that is pushing in the NE direction. Correlating the seismological and GPS analysis has enabled the construction of a tectonic model for the Sinai Peninsula.

http://iopscience.iop.org/article/10.1088/1742-2132/5/4/010/pdf

A tectonic model of the Sinai Peninsula based on magnetic data

This work presents new seismological and Global Positioning System (GPS) results aimed at understanding the nature and rate of strain associated with the opening of the Suez rift that separates the Sinai sub-plate from the African plate. The Sinai sub-plate has played a significant role in the tectonic evolution of the northern Red Sea and the Eastern Mediterranean region. Most small, moderate and large earthquakes occur within belts associated with the geologically documented borders of this sub-plate including the Dead Sea fault (DSF) system in the east, the Cyprian arc (CA) in the north, and the Suez rift (SR) to the southwest. The DSF and CA are well defined; however, the SR is only partially defined. Earthquake foci distribution supports the idea that the SR is seismically active, and this earthquake activity cannot be ignored throughout the kinematics evaluation of northern Red Sea region. The earthquake activity is relatively higher in the southern part of the SR and gradually decreases northward. The high seismicity is mainly attributed to the presence of the Sinai triple junction. Earthquake focal mechanisms in the SR are dominated by oblique normal faulting with left-lateral strike-slip components on NW trending fault planes consistent with regional kinematics. The extensional semi-principal stress axes derived from fault plane solutions are oriented NNE-SSW in good agreement with the current stress field obtained from borehole breakouts along the SR as well as results from GPS surveying. Recent survey-mode GPS observations provide evidence for coherent northerly motion of the Sinai sub-plate that varies between 2 and 5 mm/yr. Moreover, strain analysis indicates that the southern SR is dominated by extension while its northern segment is characterized by constriction, inconsistent with earthquake focal mechanisms and regional tectonic models. The overall northward motion of the Sinai sub-plate indicates that slab-pull rather than ridge-push is the dominant force controlling regional kinematics. Based on the low rate of extension and lack of oceanic crust, the SR can be considered an incipient plate boundary between the Sinai sub-plate and the Nubian plate.

Seismological and gps constraints on sinai sub-plate motion along the suez rift

Using Shen’s method (Shen et al., 1996), deformations of the Earth’s crust in Azerbaijan were studied based on GPS measurements. For estimating the rate of deformation, we used the field of velocity vectors for Azerbaijan, Iran, Georgia, and Armenia that were derived from GPS measurements during 1998–2012. It is established that compression is observable along the Greater Caucasus, in Gobustan, the Kura depression, Nakhchyvan Autonomous Republic, and adjacent areas of Iran. The axes of compression/contraction of the crust in the Greater Caucasus region are oriented in the S-NE direction. The maximum strain rate (approximately 200 × 10−9 per annum) is documented in the zone of mud volcanism at the SHIK site (Shykhlar), which is marked by a sharp change in the direction of the compression axes (SW-NE). It is revealed that the deformation field also includes the zones where strain rates are very low approximating 5 × 10−9 per annum. These zones include the Caspian-Guba and northern Gobustan areas, characterized by extensive development of mud volcanism. The extension zones are confined to the Lesser Caucasus and are revealed in the Gedabek (GEDA) and Shusha (SHOU) areas, as well as in the zone located between the DAMO and PIRM sites (Iran), where the deformation rate amounts to 100 × 10−9 per annum. It is concluded that the predominant factor responsible for the eruption of mud volcanoes is the intensity of gas-generation processes in the earth’s interior, while deformation processes play the role of a trigger. The zone of the epicenters of strong earthquakes is correlated to the gradient zone in the crustal strain rates.

GPS-based crustal deformations in Azerbaijan and their influence on seismicity and mud volcanism

Geodetic constraints on Rupturing of Continental Lithosphere along the Red Sea Robert Reilinger, Simon McClusky, Abdullah ArRajehi, Salah Mahmoud, Ali Rayan, Woldai Ghebreab, Ghebrebrhan Ogubazghi, and A. Al-Aydrus Department of Earth, Atmospheric, and Planetary Sciences, MIT, Cambridge, MA 02139 USA, King Abdulaziz City for Science and Technology, Riyadh, Kingdom of Saudi Arabia, National Research Institute of Astronomy and Geophysics, Helwan, Cairo, Egypt, Asmara University, Asmara, Eritrea, Faculty of Science, Sana’a University, Yemen

http://www.utdallas.edu/%7Erjstern/egypt/PDFs/Cenozoic%20Red%20Sea/ReilingerRedSeaGPS.pdf

Woldai Ghebreab

Papers

Geodetic constraints on Rupturing of Continental Lithosphere along the Red Sea