Traces of Strong Eneolithic and Medieval Earthquakes Hitting the Durankulak Archaeological Settlement in Northeastern Bulgariaстатья
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Аннотация:We have conducted paleo- and archaeo-seismic surveys in the Durankulak Eneolithic archaeologicalsettlement in northeastern Bulgaria, identifying many earthquake-related deformations of different ages.The ubiquitous presence of counterfort walls added to damaged original (nearly north–south) walls on theeastern side provides evidence of the first significant earthquake in Durankulak that seems to have occurredduring Middle to Late Eneolithic time (4650–4100 B.C.). This seismic event made the north–south walls tiltwestward, so that the ancient residents had to build counterfort walls to prevent the original walls from collapsing.However, the upper excavations in the archaeological settlement show that the next, later, seismicdeformation induced a tilting and collapse of remains of the original walls eastward, producing a gap of a fewtens of centimeters between the original walls and the counterfort walls. Afterwards the settlement was abandoned.It may be surmised that the later earthquake was stronger than the earlier one, which left room forreconstruction work. The local seismic intensity of the earlier earthquake seems to have been at least Il ≥ VIIIgrades, while the later event had Il ≥ IX on the МSК-64 scale. Considering that the masonry of both walls,the original and the counterfort ones, is about the same age, the time interval between the two seismic eventsmust have been short, one or two hundred years. Nevertheless, the epicenters of both of these earthquakeswere to different directions from Durankulak. The seismic motion (compressive waves and shocks) went fromthe west during the first earthquake and from the east during the second. The rupture zone of the first seismicevent was obviously related (1) to an earthquake-generating zone in continental Bulgaria situated west of thearchaeological settlement in question, or (2) to the Intramoesian active fault that was responsible for the largeearthquake of 1444. The rupture zone of the second seismic event was nearby, in the coastal part of the BlackSea; the responsible feature seems to have been the Shabla–Kaliakra earthquake-generating zone. Considerableseismic deformations were also identified in structures on the southern slope of the island in a dwellingdating back to the First Bulgarian Kingdom (the 9th century A.D.). This seismic event produced distortionsin the walls (in map view), sigmoidal patterns, as well as fractures and rotations in the walls. The local seismicintensity due to this earthquake is supposed to be at least Il ≥ VIII grades. The rupture zone of a third seismicevent was likely to be nearby, in the coastal part of the Black Sea, and the responsible feature must have beenthe Shabla–Kaliakra earthquake-generating zone.