Lake Van (Southeastern Turkey) Experiment: Receiver Function Analyses of Lithospheric Structure from Teleseismic Observa
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Pure and Applied Geophysics
Lake Van (Southeastern Turkey) Experiment: Receiver Function Analyses of Lithospheric Structure from Teleseismic Observations HAMDI ALKAN,1
HAKAN C¸ıNAR,2 and SERGEY ORESHIN3
Abstract—The P and S wave receiver functions and their joint inversions are used to study the lithosphere beneath the Lake Van region using approximately 600 teleseismic earthquake data (Mw C 5.8) at different azimuths collected from 10 permanent broadband stations operated by Kandilli Observatory and Earthquake Research Institute and Disaster and Emergency Management Authority in the region. The dataset is taken from the European Integrated Data Archive. The simulated annealing method is used for the joint inversion of P-wave and S-wave receiver functions, since the P410s phase cannot be detected reliably in the depth stacks. This may be due to the low olivine content and high basalt content at this depth. The inversion process is therefore performed without travel time residuals. The crustal thickness is observed at nearly 45 km in all the velocity models obtained from the inversion. The relatively low-velocity layer (Vs = 3.4 km/s) at depths of the middle crust may be associated with volcanic centers near Nemrut, in the west of the region. Additionally, another low-velocity layer (Vs = * 3.0 km/s) is observed in the upper crust around the Su¨phan Volcano. Also, Vp/Vs and Poisson’s ratios are calculated for the study area. Their high values (Vp/Vs C 1.85, and r C 0.285) correspond to the partial melting of the lower crust in the region. According to velocity models obtained from the inversion results, the most important outcome is that the average variance of the Moho discontinuity (* 45 km) and lithosphere– asthenosphere boundary (* 90 km) under the seismograph stations can be interpreted as a likely part of the Arabian oceanic plate in relation to the collision zone. Keywords: Lake Van region, crust, lithosphere–asthenosphere boundary, receiver functions, joint inversion.
1
Department of Geophysical Engineering, Van Yu¨zu¨ncu¨ Yıl University, 65080 Van, Turkey. E-mail: [email protected] 2 Department of Geophysical Engineering, Karadeniz Technical University, 61080 Trabzon, Turkey. 3 Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, 123242 Moscow, Russia.
1. Introduction Eastern Anatolia is one of the most seismically active regions, and its tectonics is influenced by an active collision zone, which began * 11 My ago, between the Arabian Plate (northerly moving * 18 mm year-1) in the south and the Eurasian Plate (* 5 mm year-1) in the north (Keskin 2003; S¸ engo¨r et al. 2003; Reilinger et al. 2006; Keskin 2007). Compression of these plates causes westward escape and counterclockwise rotation of the Anatolian Plate (* 21 mm year-1) along the two prominently large transform faults, viz. the North Anatolian Fault Zone (NAFZ) and East Anatolian Fault Zone (EAFZ) (S¸ engo¨r and Kidd 1979; S¸ engo¨r and Yılmaz 1981; Keskin 2003; S¸ engo¨r et al. 2003; Reilinger et al. 2006). Also, veloci
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