LITHOSPHERIC STRUCTURE IN EASTERN TURKEY

The East Anatolian Plateau is a region with an average elevation of 2 km exhibiting actively deforming and with widespread Pliocene to recent volcanism. The tectonics of Turkey and the Anatolian Plateau can be described as the convergence of three continental plates: The Anatolian sub-plate, the Arabian plate, and the Eurasian plate which form a diverse suit of tectonic boundaries. Collision of the Arabian and Eurasian plates is occurring along the East Anatolian Fault Zone (EAFZ) and the Bitlis suture. The Eastern Turkey Seismic Experiment (ETSE) was conducted across the East Anatolian plateau and the northernmost Arabian plate from October 1999 until August 2001. ETSE was a 29 broadband seismic station network that was designed to improve our understanding of the Bitlis-Zagros thrust zones, as well as the nature of continental escape along the East Anatolian Fault Zone (EAFZ) and the North Anatolian Fault Zone (NAFZ).

An automated network triggering algorithm based on STA (short term averaging) and LTA (long term averaging) was used to detect seismic events occurring within the ETSE array. A total of 1165 earthquakes were located and classified into four different categories based on the reliability of the locations as established by the data coverage. We used a grid search approach and phase data from 66 very well located events evenly distributed throughout the Anatolian plateau in order to determine the optimal 1-D velocity model. The results show that seismic activity in Eastern Turkey is higher than previously documented. Furthermore we found there were no subcrustal earthquakes beneath the Arabian-Eurasian collision zone or beneath the Anatolian Plateau recorded during the ETSE deployment. This result suggests no or very little underthrusting of the Arabian plate beneath East Anatolian Plateau. Our results also suggest that the North Anatolian Fault Zone extends farther toward the southeast, well beyond the Karlıova triple junction, and that a number of unmapped active, seismogenic faults exist in the region. The crust thickens from 42 km near the southern part of the Bitlis suture zone to 50 km along the northern edge of the Anatolian plateau in the vicinity of the NAF. In the east, crustal thickness increases from 40 km in the Northern Arabian plate to 46-48 km in the middle of the Anatolian plateau.