Seismic Deformations at Archaeological Sites, in Sediments, and the Relief of Mt. Opuk, Crimea

Abstract

The study of archaeological sites in the area of Mt. Opuk (southeast Crimea) allow us to outline approximately the chronology of seismic events. The revealed deformations of building structures, taken separately, and, moreover, taken together, indicate their seismogenic character. In ancient building structures and cultural layers of archaeological sites in the Mt. Opuk area, numerous ruptures were identified. Fissures found in the ash dump, fading in the layer of the end of the 2nd–3rd century CE are typical seismogenic ruptures. It is possible that this earthquake occurred at the end of the 3rd century. The traces of two earthquakes are found at the Hill A settlement. The first earthquake is reflected in systematic clockwise rotations of the submeridional walls around the vertical axis. The seismic oscillations from this earthquake were directed at an angle to the mentioned walls, along the NNE–SSW axis. The building was preserved and repaired (buttress wall at the northern face of the southern wall of room A). The second earthquake, which was stronger, caused surface rupturing and displacements in the SE part of the building, almost completely destroying it. The time when this room was destroyed dates back to the beginning of the 4th century BCE. Traces of catastrophic destruction are documented in the ruins of a citadel on the upper plateau of Mt. Opuk; the NW tower of the citadel experienced significant deformations; traces of two earthquakes are found in the barracks; the western curtain wall and the citadel wall were severely damaged. Significant seismic deformations were also studied on the so-called eastern defensive wall, which is most likely synchronous with the citadel. The citadel completely ceased to exist in the first half of the 6th century CE, possibly after a strong seismic event, which was the final one in a series of destruction of the ancient Kimmerikon infrastructure. Before the Saltovo-Mayatsk people arrived at the Kerch Peninsula, no traces of human settlements on Mt. Opuk or its vicinity were reported. The traces of two earthquakes are revealed in the manor belonging to the Saltovo-Mayatskii (Khazarian) period of the early medieval time. The first seismic event led to counterclockwise rotation of all submeridional walls of the manor around the vertical axis. This shows that the seismic impact was directed at an angle to these building elements, namely, along the NNW–SSE axis. The building was preserved; only a retaining wall was erected at the southern (outer) face of the eastern wall of the room. The second earthquake was stronger: its intense seismic shaking collapsed both repaired and retaining wall in the southern direction, from where elastic waves arrived. The manor finally perished in the 930s–940s CE. Remarkable traces of strong earthquakes are observed in the topography of Mt. Opuk. According to the collected data, the main rupture on the mountain is seismotectonic in nature; however, the offset value was intensified multifold owing to seaward slip of the rock volume. The fault is a segment of the South Kerch fault zone, which is traced along the Black Sea coast. The last seismotectonic slip dated here in the area of the ancient city of Kitaia is thought to have occurred in the 3rd century CE, or immediately thereafter. Over approximately the past 4000 years, at least three seismotectonic slips have occurred here with a total offset of 3 m or more. The minimum traced length of the activated segment is 20 km. Using the known global relationships for the parameters of seismic ruptures, the minimum magnitude of this event can be estimated at M_W = 6.6–6.9.