Earthquake Rupture in Ancient Cnidus, SW Turkey
by
Erhan Altunel
1. Osmangazi University, Engineering Faculty, Dept. of Geology, Eskisehir, Turkey
Coauthors: Iain Stewart (Brunel University, Department of Geography and Earth Sciences, Uxbridge UB8 3PH, UK), Aykut Barka (Deceased; formerly of ITU, Eurasian Earth Science Institute, Istanbul, Turkey)

Cnidus was established as a major maritime trading centre in the 4th century BC and retained an active economic, cultural and artistic life into Roman and early Byzantine times, exploiting an influential coastal position at the western end of the Datça Peninsula, southwestern Turkey. The history of the city's demise is less clear, though it involved coastal attacks by Arab raiders in the 7th century AD and then, later, a number of devastating earthquakes. Archaeologists have speculated that the abandonment of the city may have been related to these earthquakes. Certainly the western Datça peninsula is extremely seismically active, lying midway between the Hellenic arc plate boundary to the south and a major normal fault system in the Gulf of Kerme to the north. Damaging earthquakes struck the peninsula in 1933 (M 6.5) and 1956 (M 7.2), and historical catalogues locate a number of destructive shocks in this region (e.g. 141/142 AD, and 1493 AD, 1865 AD).

Field studies show that the ancient city of Cnidus lies directly on an active fault. The fault is a roughly E-W trending normal fault with a surface length of at least 8 km. The ruins of the city occupy the southern downthrown block and their northern extent terminate against the prominent limestone fault escarpment. Indeed, the fault scarp forms the backwall of the Sanctuary of Demeter, where several rock-cut niches have been carved into the smooth limestone fault surface. Similarly, the famous Round Temple of Aphrodite is set into the bedrock scarp. In both locations, built constructions are warped and displaced close to the fault. This is most significant at the Round Temple of Aphrodite, where the circular podium itself is cut and vertically offset (~35 cm) by the fault. Striations on the underlying bedrock fault plane are consistent with the opening directions of displaced blocks within the alter, confirming that the rupture is tectonic rather than gravitational. As well as this evidence for primary fault rupture, there are other signs of strong seismic damage at the site (collapsed walls and buildings). Most notably, collapsed columns in the stoa have fallen parallel to each other and lie directly on a destruction layer in which there is evidence of burning. Archaeological studies report comparable burning levels from elsewhere in the site, but confirmation of synchronous site-wide destruction awaits precise dating of these destruction horizons. Nevertheless, the new geological data strengthens the view that the city of Cnidus was abandoned as the result of a devastating earthquake.

Date received: July 18, 2002