Investigation of local site responses at the Bodrum Peninsula (Southwest of Turkey) using the mainshock and aftershocks of the 20 July 2017 Mw6.6 Bodrum-Kos earthquake

Abstract

Bodrum Peninsula located in the province of Mugla is situated in southwest Turkey. The peninsulais one of themost populatedtouristic centersof the southwest coast of Turkey, near the Aegean Sea.However, this region is surrounded by numerous active seismic entities. All of those systems have capability of producing large magnitude earthquakes and pose a great threat to settlements in and around of this region. Considering the high seismic risk and population of the peninsula, a strong ground motion monitoring system was deployed in June 2015. So far the network recorded many earthquakes in different magnitude and distances. In this study, a dataset with 51 events with momentmagnitudes from 4.0-6.6 occurred within 100 km epicentral distances were selected for site effect calculation. This datasetincludes the mainshock and its significant aftershocks recordsof the Mw6.6 Bodrum-Kos earthquake(20 July 2017, 22:31 UTC). Predominant frequencies and amplification values of shallow soil layers under the stations were estimated through Horizontal to Vertical Spectral Ratio and Standard Spectral Ratios. The results indicate that predominant frequencies change between 2.1 - 2.7 Hz for soft soils, where it is 4.8 Hz for the reference site B5, and relative amplifications are in the range of 1.0 to 6.6. Then, sediments thicknesses beneath the stations were empirically calculated by using predominant frequencies. In addition, the damage distribution of the Bodrum-Kos earthquake was discussed with its relation to the estimated resonance frequencies and relative amplifications. Observations regarding to the Mw6.6 earthquake have revealed that unreinforced masonry structures, in particular, old stone houses were damaged while there were generally no apparent structural damage at reinforced buildings.