Coseismic (20 July 2017 Bodrum-Kos) and paleoseismic markers of coastal deformations in the Gulf of Gokova, Aegean Sea, SW Turkey

Abstract

The Gulf of Gokova is one of the earthquake-prone areas in the Aegean Sea and southwestern Turkey. The paleoseismology of the region is not well known because of the lack of robust field data. In this study, we focused on marine tidal notches as geomorphic markers of modern and paleoseismic deformations. Our geomorphic surveys suggest that the 20 July 2017 Bodrum-Kos Earthquake coseismically uplifted the Karaada Islet at the Turkish coast. We also provide new observations for the entire coastal area of the Gulf of Gokova. The six well preserved uplifted notch levels up to 1.5 m a.s.l. at the east of Oren town are geomorphic markers of offshore earthquakes along the northern shores. Radiocarbon dating C-14 results suggest that the last 0.5 m of this uplift occurred in the last 2314 +/- 32 years. The four well-preserved marine tidal notches up to 1.2 m a.s.l. indicate the earthquake-related uplift along the southern shores. There are also submerged shorelines along the southern shores at 1 m and 3-4 m below sea level as geomorphic markers of relative sea-level change. The evidence of a longer-term deformation is the presence of an uplifted wave-cut marine terrace on the southern shore. We do not have age data, but the inner edge elevation of the terrace is 238 m above modern sea level. In this study, we reveal that the shores of the Gulf of Gokova have been uplifting since the Pleistocene and Holocene, with a high probability of large magnitude offshore earthquakes occurring on normal faults very close to the modern shoreline.