In search of fault(s) responsible for the historical earthquakes at the ancient city of Sagalassos (SW Turkey)

Dominique Similox-Tohon1, 2, Manuel Sintubin1, Philippe Muchez2 & Marc Waelkens3

1 Structural Geology & Tectonics Group, K.U.Leuven, Redingenstraat 16, 3000 Leuven, Belgium

2 Fysico-chemische Geologie, K.U.Leuven, Celestijnenlaan 200C, 3001 Leuven, Belgium

3 Department of Archaeology, K.U.Leuven, Blijde Inkomststraat 21, 3000 Leuven, Belgium

dominique.similox-tohon@geo.kuleuven.ac.be

The ancient Pisidian city of Sagalassos, located some 10 km SSW of Isparta (SW Turkey), developed into a prosperous town during Hellenistic and Roman times. Archaeological evidence shows that Sagalassos has been damaged by earthquakes during Roman and Byzantine times. The city was eventually abandoned around the middle of the 7th century AD after a devastating earthquake. Structural damage from that last seismic event suggests that Sagalassos was located in the macroseismic epicentre of this earthquake. The causative fault(s) has(have) not yet been identified.

To identify the active faults in the vicinity of Sagalassos, Landsat 7 images and a digital elevation model were analysed. Characteristic geomorphological features and drainage patterns for active normal faults in both resistant and less-resistant lithologies were observed. On some of these normal faults major earthquakes occurred in the 20th century. However, Sagalassos is located outside the macroseismic epicentre of these earthquakes. In the field, some of the lineaments in the near vicinity of Sagalassos show indications of normal faulting. These faults juxtapose Mesozoic limestones (in the footwall) with Quaternary colluvium (in the hanging wall). They are characterised by typical rocks (incohesive breccia belt and compact breccia sheet) and tectonic tool marks on the fault planes (corrugations, comb fractures, hangingwall breccia trail and pluck holes). This particular architecture leads to a characteristic degradation. In the study area the degradation is in an advanced state, so that a conclusive identification of different lineaments as active normal faults remains rather problematic.

The ENE-WSW-trending limestone range front, overlooking the city of Sagalassos to the north, is interpreted as an active normal fault based on remote sensing analysis. Although in the field no direct evidence has yet been found for faulting, this mountain face could correspond to a degraded fault scarp. In the city active normal faulting is evidenced on different 2-D resistivity profiles and by several faulted archaeological relics. It is suggested that an active normal fault passes through the ancient city. This fault could be regarded as a potential causative fault for the 7th century AD earthquake.

The approach applied in search of the causative fault(s) seems to be reliable and allowed us to propose a causative fault for the 7th century AD earthquake. The remote sensing analysis identified both known and unknown active normal faults. These normal faults were identified in the field. It is, however, clear that the advanced degradation of the fault scarps hinders the conclusive identification of active normal faults.

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