Probabilistic seismic hazard evaluation of eastern Anatolia observatory

The Eastern Anatolia Observatory (DAG), to accommodate a 4-m telescope, is under construction in the city of Erzurum at Karakaya Peak of the Palandöken Mountain Range. Owing to the vulnerability of the telescope and its optical components to earthquakes and the high demand for pointing accuracy for quality astronomical observations, the seismic hazard needs to be reliably determined before any design and construction work begins. A relevant rectangular zone, extending 250 km from the observatory in each direction, is selected as the study area. Then, the seismic hazard at the DAG site is estimated by using the probabilistic hazard analysis method. Using different magnitude scales, several earthquake catalogues are recompiled by converting them into a uniform moment magnitude (Mw) scale, and the seismic sources that could affect the study area are determined. The results are aggregated for epistemic uncertainties using the logic-tree method. Finally, peak ground acceleration (PGA) values are obtained for two recurrence periods corresponding to two different design levels (operating basis and design basis earthquakes) using two different ground motion attenuation models. The disaggregation of the seismic hazard permits association of the PGA estimates with various faults. Disaggregation also provides source information for synthetic ground motion generation. Effects of rupture directivity and topographical amplification are discussed.