Late Quaternary Uplift Records from Datça Graben and Cnidus Ancient City, SW Turkey: Sea Level Changes Versus Tectonics

The Datça Graben at southwestern Anatolia is a WNW-trending, seismically active depression, evolving since Pliocene. This tectonic activity is controlled by normal faults, which have effected ancient settlements. Cnidus city (Old and Modern) –an ancient mercantile centre in Hellenistic, Roman and Byzantine periods– is one of these residentials, keeping records of this activity. The ancient harbour walls of Cnidus, lying 2.2-4.0m under the sea, comprise important traces about the sea level changes and tectonics over the past 2.6kyr. And this study discusses possible reasons of these traces in terms of sea-level changes and tectonic activity.
Paleostress analysis along boundary faults in the Datça Graben present almost N–S oriented pure tensional stress regime, compatible with earthquake focal mechanism solutions located around Datça Peninsula. Additionally, almost E−W trending surface rupture of a historical earthquake in Modern Cnidus, representing similar characteristics with paleostress analysis, give further support to the ongoing extension along the Kızlan, Karaköy and Cnidus faults. Previous studies concerning late Quaternary sea-level changes around peninsula demonstrate 1.0-1.25m lower sea level for 2.6kyr ago.
Taking into account the depth of harbour remnants of the Old Cnidus and regional sea-level records, it can be inferred that regional tectonics has significant effect besides sea-level changes. Our calculations show that the Datça Graben is subsiding with 0.365-0.461mm/yr. rate for the central and 1.057-1.153mm/yr. for the southern part. These values match with other areas around the peninsula and earthquakes recorded in historical and instrumental era proves the earthquake potential.