Investigation of lithospheric deformation and mantle anisotropy beneath Central Anatolia from Shear Wave Splitting Analysis

Abstract:

With the primary objective of investigating the upper mantle anisotropy beneath central Anatolia-Turkey, we have performed shear wave splitting analysis and calculated the fast polarization directions and time-delays benefiting from teleseismic earthquakes recorded by a dense temporary seismic network consisting of 65 broadband sensors that were deployed in early May 2013 and operated for two years as a part of CD-CAT project (Continental Dynamics Central Anatolian Tectonics, funded by NSF with instruments supplied by PASSCAL depository). To further enhance the station coverage in the region, we also included data from 45 permanent broadband stations of Kandilli Observatory and Earthquake Research Institute (KOERI). During the analysis, we have used the SplitLab software to determine splitting parameters of the records from only SKS and SKKS phases. Our initial results were derived from teleseismic earthquakes (with magnitudes greater than 5.8) that occurred within the time period from May-2013 to 2014. The average fast polarization directions obtained from stations located in the vicinity of the East Anatolia Fault Zone are well aligned with the fault trend indicating NE-SW orientations. Furthermore, we did not observe significant variations in the polarization directions and the delay times along the fault zone. Stations deployed in the vicinity of Central Anatolian fault zone exhibit N-S fast directions in good agreement with the fault trend. The average delay time for the whole study area is slightly higher than 1 second. Rapid spatial variations in splitting parameters are observed only in Adana region and the surrounding area. This probably suggests that the contribution of crustal anisotropy to mantle anisotropy is quite high. This observation is also consistent with the known tectonic structure of this region, which is presumably related to fabrics within deep crustal rocks preserving a record of deformation. This point should also need to be supported with further anisotropy studies. Furthermore, the anisotropy models can be used to infer the depth distribution of the inferred mantle strain. These observations will help confirm whether there is a strong coupling between deformation in theasthenosphere and lithosphere and whether this is helping to aid in the extrusion of the Anatolian plate.