Seismic Deformations in the Archaeological Sites of Varna, Bulgariaстатья
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Дата последнего поиска статьи во внешних источниках: 4 марта 2022 г.
Аннотация:The ruins of Odessos are located on the territory of Varna, Bulgaria. Archaeoseismological studies carriedout at the archaeological sites of ancient Odessos revealed some significant damage and destruction in the ancientbuilding constructions. These are numerous breaks, tilts, protrusions and turns of wall parts, longitudinal asymmetricdeformation of the above-entrance arch, lateral in plan bending of the extended wall, outward knock-out of thestone blocks and intensive cracking. We attributed traces of subsequent shoddy repairs, which sometimes involvedusing single expensive stone blocks taken out of the ruins, as circumstantial evidence of strong earthquakes that hadoccurred here. Interestingly, medieval builders already knew about the possibility of strong earthquakes in the regionand put wooden longitudinal beams in the walls to absorb vertical seismic vibrations. The degree of destruction anddamage in medieval buildings built on loose fill soils increased due to subsidence. Archaeological research established6 periods of construction in ancient Odessos: Using this periodization, we calculated the age of past seismicevents: 1) around the 1st century A.D. — the destruction of the Late Hellenistic fortress wall; 2) the early 5th century—the early 6th century (a cluster of at least 3 strong earthquakes, judging also by deformations in the Bishop’sBasilica of Odessos (Minchev et al., 2020)): dismantling of the fortress wall, discontinued use of both thermae. Thegate of Odessos remains in operation after repairs. There is low quality construction of houses. Accumulation of tiledebris; 3) the destruction of the Orthodox church in the 1444 earthquake. We were able to determine the averagedirection of the maximum aggregate seismic movements that destroyed the large and small thermae, as well as theexcavated segment of the fortress wall and the Odessos gate complex. They propagated along the WNW-ESE axis,most likely from the Shabla-Kaliakra seismogenic zone. The deformations of the 13th-century Orthodox churchwere caused by seismic vibrations that propagated in the submeridional direction from one of the seismically activefaults south or north of Varna, although they may have been affected by ground subsidence. Thus, as a result of thestudies, we were able to detect traces of yet unknown strong earthquakes, to determine their age and direction to theancient epicentral zones. The intensity of seismic vibrations during all these earthquakes was Il = VIII—IX MSK-64.The data obtained can be used to improve the seismic hazard assessment of Varna and NE Bulgaria.