NEOTECTONICS AND SEISMICITY OF ERZURUM PULL-APART BASIN, EAST TURKEY
A. Koçyiğit1, M.C. Canoğlu2
1Middle East Technical University, Department of Geological Engineering, Active Tectonics and Earthquake Research Lab, TR-06800 Ankara, Turkey, akoc@metu.edu.tr
2Sinop University, Faculty of Engineering and Architecture, Environmental Engineering Department, TR-57000 Sinop, Turkey, mccanoglu@sinop.edu.tr
Keywords: Erzurum, pull-apart basin, strike-slip neotectonic regime, active fault, East Anatolian tectonic block
Abstract
The study area is the Erzurum pull-apart basin located in the East Anatolian Tectonic Block (EATB), which is under the control of a strike-slip neotectonic regime since the beginning of the Quaternary. The Quaternary Erzurum pull-apart basin is an about 1-30 km wide, 90 km long and actively growing strike-slip depression. It is bounded by the Erzurum-Dumlu sinistral strike-slip fault zone to the east-southeast, by the Aşkale sinistral srike-slip fault zone to the north-northwest, and by the Başköy-Kandilli reverse fault zone and the N-S-trending Ilıca oblique-slip normal fault set to the west. The Erzurum pull-apart basin was evolved by the deformation and subdivision of an E-W-trending older intermontane basin. The new basin has a 0.5 km thick, flat-lying (undeformed) and unconsolidated fill, which overlies, with an angular unconformitry, the deformed (folded and faulted) basement rocks of pre-Quaternary age. Basin fill consists of coarser-grained marginal facies (fault terrace, fan, fan-apron, and superimposed fan deposits) and finer-grained depocentral facies represented by floodplain to organic material-rich marsh deposits. All gradations are seen among these lithofacies. The seismicity of the Erzurum pull-apart basin is quite high. The magnitude of the peak earthquake to be sourced from the active faults (e.g., the Erzurum fault) is about Mw = 7.0. This was proved by both the historical and recent earthquakes. Numerous settlements in the size of a large city (e.g., Erzurum), county, town, and small villages with a total population of over 766.000 are located in and along the active fault-bounded margins of the Erzurum pull-apart basin. They are under the threat of destructive earthquakes to be sourced from the margin-boundary faults. Therefore, based on both the active fault parameters and the water-saturated basin fill, a large-scale earthquake hazard map has to be prepared. This map has to be used in both the earthquake hazard to risk analyses and the redesign of city planning and all type of constructions in Erzurum and other settlements in this region.
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