Tectonics of the Eastern Part of the North Caspian Depression
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We use observations of surface faulting, well-constrained earthquake focal mechanisms and centroid depths, and velocity structure determined by surface wave propagation and teleseismic receiver functions to investigate the present-day deformation and kinematics in and around the South Caspian Basin. The lack of earthquakes within the basin itself indicates that it behaves as a rigid block, though its sedimentary cover is deformed by numerous folds that are decoupled from its rigid basement by overpressured mud. The basin contains a sedimentary sequence almost 20 km thick above a relatively high-velocity basement that is thinner within the basin than on its margins. The basement beneath the basin could be either unusually thick oceanic crust or thinned, but relatively high-velocity, continental crust. The South Caspian Basin is surrounded by active earthquake belts on all sides. No earthquakes deeper than 30 km can be confirmed in the Kopeh Dag, Alborz and Talesh, which bound the NE, S and W sides of the basin. In contrast, earthquakes occur to depths of at least 80 km on the Apsheron-Balkhan sill, which bounds the N side of the basin and where no earthquakes can be confirmed that are shallower than 30 km. We interpret these deeper earthquakes to indicate the onset of subduction of the South Caspian Basin beneath the central Caspian, a process that appears to occur aseismically at shallow levels. Although oblique shortening is partitioned into pure strike-slip and pure thrust in many areas, conjugate right-lateral and left-lateral components in the Kopeh Dag and eastern Alborz suggest that the South Caspian Basin has a westward component of motion relative to both Eurasia and Iran. This motion enhances westward underthrusting of the basin beneath the Talesh mountains of Iran and Azerbaijan. We estimate the present motions of the South Caspian Basin to be ∼13–17 mm yr−1 to the SW relative to Iran (a maximum value) and ∼8–10 mm yr−1 to the NW or NNW relative to Eurasia. We suspect that these motions are all relatively recent, and may have begun only in the Pliocene (3–5 Ma). The South Caspian Basin will ultimately be destroyed by subduction or underthrusting and its present situation may represent an intermediate stage between that of the eastern Mediterranean and that of the seismically active slab beneath the Hindu Kush.
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Abstract The southern part of the South Caspian oil and gas Basin (SCB) is one of the main oil and gas producing regions in the central part of Eurasian continent. The large number of offshore oil and gas fields is located here, therefore the basin considered as a promising direction for the further perspective zones survey. The basin is located between the uneven-aged mountain structures of the Lesser and Greater Caucasus in the west, the Great Balkhan and Kopet-Dag in the east, the Talish and Elbrus ridges in the south. In the north, it is limited by a sub-latitudinal regional deep fault, which fixes the northern slope of the complex Absheron-Balkhan zone of uplifts, which is part of the South Kura and Western Turkmenistan depressions. Among the structural elements of the second order, the South Absheron depression, the complex Abikh swell and the Javadkhan-Natevan zone in the west should be noted; Turkmen terrace, Ogurchinskaya step and Chikishlyar-Fersmanovskaya-Weber-Western zone in the east (Fig. 1). The central place in the structure of the basin is occupied by the South Caspian Mega Depression (SCMD), in the most submerged part of which - the pre Elbrus Basin - the basement lies at a depth of about 25 km, and the sedimentary stratum, including Mesozoic, Cenozoic and Quaternary formations, is largely represented by the Pliocene - post-Pliocene sediments, reaching a total thickness of 8–10 km and more in the troughs (Fig. 2, 3).
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