Investigation of Local Site Responses at the Bodrum Peninsula, Turkey

Bodrum Peninsula is situated on the southwest coast of Turkey, near the Aegean Sea coast. The Peninsula extends ~42 km in the E-W direction and ~15 km in the N-S direction between the Gulfs of Gulluk and Gokova. The Bodrum peninsula with a population over a million in summer season is one the touristic centers of Turkey. The region is also surrounded by numerous active seismic entities such as Ula-Oren Fault Zone, Gokova Graben, eastern part of the Volcanic Arc and Hellenic Arc-Trench System etc. These systems demonstrate high seismic hazard and pose a great threat to settlements in and around the region. Considering the high seismic risk and high population of the peninsula, a strong ground motion monitoring system, consists of five accelerometric stations, was deployed in June 2015 by Bogazici University, Kandilli Observatory and Earthquake Research Institute (KOERI), Earthquake Engineering Department. Three out of five stations (B1, B2 and B3) are on alluvium sediments. The rests are on Limestone (B4) and Volcanic rock (B5). Up to now the network has recorded more than 100 earthquakes. Among the dataset, 25 events with magnitudes (Ml) from 3.0 to 5.5 occurred within 200 km epicentral distances were selected for site effect calculation. 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 (1) predominant frequencies change between 2.1 and 3.5 Hz for soft soils, where it is 5.8 Hz for the reference site, (2) relative amplifications are in the range of 2.3–6.8, and (3) empirically estimated sediments thickness beneath the B1, B2 and B3 stations vary between 35.6 and 64.2 m.