Traces of Seismic Activity in Architectural Monuments in Derbent, Dagestan

Abstract

As a result of studies conducted in the city of Derbent, it is established that its monumental fortification structures erected at the end of the 560s AD underwent numerous strong seismic shocks during their existence. The number and approximate ages of the strong seismic events that affected Derbent throughout its history are determined by the age of the deformed stone masonry. Five episodes of seismogenic destructions are identified. Clockwise rotations around the vertical axis along the interblock joints at the segment of the Sasanian masonry of the curtain wall and the tower of the southern wall of the citadel are noted to occur in late Sasanian and early Arab times (from the 6th century to the beginning of the 8th century). They were large in value and caused by seismic action. Numerous cases of rebuilding and relaying in the defensive walls of the city are also revealed. The building works during the Arab period, especially in the 8th century, described in written sources, were probably caused not only by the military confrontation of the Arab Caliphate and the Khazar Khaganate (the Arab–Khazar wars), which led to the damage of some segments in the defensive walls, but also by seismic activity. At the boundary of the Arab period and the rise of the Derbent Emirate (8th–11th centuries), a significant seismogenic rupture occurred in the upper part of the northern wall of the city between the citadel and the Dzharchi-Kapi Gate. The character of deformations corresponds to seismic shocks from the northwest. It is established that the repair and building works on reinforcing the defensive walls in the Sasanian citadel by later masonry (including rustication) were performed during the existence of the Derbent Emirate and in the Seljuk period. These works could be not only a consequence of destruction during the confrontation between the Derbent emirs with the city elite and the Shirvanshah state, which is described in the Tarikh al-Bab chronicle, but also as a result of the seismic destructions in the fortifications. The destruction and repair of the Juma Mosque occurred in the middle of 14th century (the 1360s). The seismic shocks, resulting in the destruction, arrived from the north. This destruction apparently caused the subsequent building activity in the Derbendi Shirvanshah period in the 15th century, especially during the reign of Khalilullah I (1417–1462), which was described in the building inscriptions and the typical features of Shirvan architecture (the Orta-Kapi Gate, Minaret Mosque). The women’s bathhouse, which was damaged by seismic oscillations propagating in submeridional direction, was repaired at the end of 18th century. The tectonic displacement of the basement blocks in the dugout of Peter the Great dates to this period as well.