Impact of regional tectonic and water stress on the seismicity in Ataturk Dam Basin: southeast of Turkey

The Ataturk Dam (AD) and Hydroelectric Power Plant (HPP), one of the biggest dams in Turkey, is located on a NE-SW axis between Adyaman and Sanlurfa, in the southeastern part of Turkey. The construction of the AD and HPP began in 1983 and after starting the impoundment in 1990, HPP initiated electric power production in 1992. AD and HPP are located in a tectonically very active region that is, bounded by the East Anatolian Fault Zone (EAFZ) to the northwest, the Bozova Fault (BF) to the southwest and the Kalecik Fault to the southeast. According to instrumental records that have been collected inquiring all available catalogues from 1900 to January 30, 2018, 42 earthquakes were recorded with magnitudes greater than 4.0 in the dam basin and its close surroundings. The scientific community is discussing whether earthquakes may be induced by pressure variations of the water level. When earthquake reports from Turkey's General Directorate of State Hydraulic Works (DSI) were examined, it was found that quite high seismic activity (1.2 <= M <= 5.2) had been recorded before the water retention in the basin. DSI, which is responsible for the dams in Turkey, has been following the seismic activity before and after water retention in the big dams since 1973 with its own local seismic network. The focal mechanism solutions of the earthquakes indicate that the tectonics of the region are controlled by right lateral strike-slip fault systems. Although the earthquakes which occurred in the region have been mostly connected with previously defined faults systems, recent earthquakes (2008 and 2017) have not been directly associated with any fault in the region. Thus, the question of whether there is a right lateral strike-slip fault buried in the region is raised. In this paper, we examine the characteristics of the tectonic structures in the region and their effect on the dam basin. We also discuss whether recent seismic series (2008 and 2017) could be connected with reservoir-induced or reservoir-triggered seismicity (RIS or RTS) or/are relevant to directly tectonic structures in a highly seismically active zone. A polygon of 20km distance from the AD and HPP was selected as the study area. On the other hand, the issue of whether seasonal changes in the water level affect seismic activity in the dam, by comparing it to other examples in the world, are discussed. In conclusion, we propose a model that explains the tectonic structures that cause the seismic activity in the region. The obtained results indicate that the seismicity in the region occurs independently of the water load.