Lithospheric velocity structure of the Anatolian plateau-Caucasus-Caspian region

Abstract

[1] The Anatolian plateau-Caucasus-Caspian region is an area of complex lithospheric structure accompanied by large variations in seismic wave velocities. Despite the complexity of the region, little is known about the detailed lithospheric structure. Using data from 31 new, permanent broadband seismic stations along with results from a previous 29 temporary seismic stations and 3 existing global seismic stations in the region, a 3-D velocity model is developed using joint inversion of teleseismic receiver functions and surface waves. Both group and phase dispersion curves (Love and Rayleigh) were derived from regional and teleseismic events. Additional Rayleigh wave group dispersion curves were determined using ambient noise correlation. Receiver functions were calculated using P arrivals from 789 teleseismic (30°-90°) earthquakes. The stacked receiver functions and surface wave dispersion curves were jointly inverted to yield the absolute shear wave velocity to a depth of 100 km at each station. The depths of major discontinuities (sediment-basement, crust-mantle, and lithosphere-asthenosphere) were inferred from the velocity-depth profiles at the location of each station. Distinct spatial variations in crustal and upper mantle shear velocities were observed. The Kura basin showed slow (∼2.7-2.9 km/s) upper crustal (0-11 km) velocities but elevated (∼3.8-3.9 km/s) velocities in the lower crust. The Anatolian plateau varied from ∼3.1-3.2 in the upper crust to ∼3.5-3.7 in the lower crust, while velocities in the Arabian plate (south of the Bitlis suture) were slightly faster (upper crust between 3.3 and 3.4 km/s and lower crust between 3.8 and 3.9 km/s). The depth of the Moho, which was estimated from the shear velocity profiles, was 35 km in the Arabian plate and increased northward to 54 km at the southern edge of the Greater Caucasus. Moho depths in the Kura and at the edge of the Caspian showed more spatial variability but ranged between 35 and 45 km. Upper mantle velocities were slow under the Anatolian plateau but increased to the south under the Arabian plate and to the east (4.3-4.4 km/s) under the Kura basin and Greater Caucasus. The areas of slow mantle coincided with the locations of Holocene volcanoes. Differences between Rayleigh and Love dispersions at long wavelengths reveal a pronounced variation in anisotropy between the Anatolian plateau and the Kura basin.

Lithospheric structure and the isostatic state of Eastern Anatolia: Insight from gravity data modelling

“…The crustal thickness in Eastern Anatolia, as determined from receiver function and seismic tomography, ranges from 30 to 55 km (e.g., Angus et al, 2006;Özacar et al, 2008;Gök et al, 2011;Gökalp, 2012;Tezel et al, 2013;Vanacore et al, 2013;Pasyanos et al, 2014;Schildgen et al, 2014;Delph et al, 2015), and the sediment thickness ranges from 0 to 5 km, based on the global sediment map determined by seismic data (Laske and Masters, 1997).…”

Crustal S-wave structure around the Lake Van region (eastern Turkey) from interstation Rayleigh wave phase velocity analyses

“…The reasons why results of average S-wave velocities are slower than global models may be connected to the shallow asthenosphere and young volcanism in the studied region. Gök et al (2011) found that the Moho is at depths of 40-42 km around the Lake Van region and estimated that low shear-wave velocities are V s = 3.2 km/s, V s = 3.7 km/s, and V s = 4.1 km/s for the depths of 10, 35, and 85 km, respectively. By checking regional waves in the crust (L g ) and the upper mantle (S n ), they observed both waves disappearing through the Eastern Anatolian Plateau, coinciding with the zones of inefficient S n propagation, and heating of a thin to absent mantle.…”

“…A vast volume of the volcanic activity in the Eastern Anatolia (~43,000 km 2 ) was produced after regional block uplift (11-13 Ma) and this process moved from the north in the Erzurum-Kars Plateau to the south-southeast in the Muş-Nemrut-Tendürek volcanoes (Keskin, 2007). Several different geodynamic models were created to explain the collision zone between the Arabian and Eurasian Plates (Şengör and Yılmaz, 1981;Dewey et al, 1986;Barazangi et al, 2006;Keskin, 2007;Zor, 2008;Gök et al, 2011;Skobeltsyn et al, 2014) and many of these were interpreted in detail by Keskin (2007). Şengör et al (2003) revealed that the East Anatolian High Plateau is deprived of mantle lithosphere, which is referred to break-off of northward subducted slab (started some 11 Ma ago) beneath the widespread melting due to direct contact with hot asthenosphere.…”

Deformation and Related Slip Due to the 2011 Van Earthquake (Turkey) Sequence Imaged by SAR Data and Numerical Modeling

“…High Vp and Vs anomalies are constrained near the surface, while low velocity zones are widely present at 20-30 km depth. The Moho depth in the Van Province is estimated to be at 42-44 km depth [17]. The low velocity anomalies are interpreted as being caused by hot lithosphere resulting from the Arabian-European plates collision, while high Vp and low Vs (corresponding to a high Poisson ratio anomaly) imply the presence of fluids ascending upward from the hot lithosphere.…”

“…The compound lithospheric structure is accompanied by large seismic wave velocities variations, and the seismic activity is intense along highly heterogeneous zones (e.g., [17]). Unfortunately, little information is available at smaller scale, e.g., for the epicentral area of the Van earthquake.…”