The 1970 Dagestan Earthquake a Half-Century Later

In connection with the 50th anniversary of the destructive Dagestan earthquake on May 14, 1970, information on the parameters, manifestation features, and consequences of this seismic event was collected and summarized. The Dagestan earthquake became a very important event in the seismic history of the entire Caucasus. The reasons for this were determined by several of its features, the most important being that it was the strongest instrumentally recorded earthquake in the Caucasus at that time, and the nearest seismic station, Makhachkala, was at an epicentral distance of less than 30 km and recorded not only the main shock, but also a strong foreshock with its aftershock sequence. After the earthquake, a temporary seismic network was quickly deployed, which made it possible to trace in detail the development of the aftershock process of the main shock. Based on the literature data, the main parameters of the Dagestan earthquake and its most important consequences are discussed. The most realistic model of the source was constructed by S.S. Arefiev et al. (2004) based on data on the inversion of body waves from this earthquake. According to this model, Dagestan earthquake had a multiple source consisting of three subsources. The initial rupture (subsource), with a horizontal extent of 14 km, was located in the center of the focal zone at a depth of 9 km. The second rupture began about 2 s later, 10 km east of the first, at a depth of about 10 km and with a horizontal extent of 20 km. The third subsource was 10 km west of the first, at a depth of 12 km. The Dagestan earthquake made it possible to significantly refine the regional seismic hazard assessment. This was extremely important in regards to construction of the Chirkey hydroelectric power plant (HPP) with a high-altitude dam (232 m) in the 8-point shaking intensity zone for this seismic event. The creation of the reservoir itself during the construction of the high-pressure concrete dam of the HPP led to the impact of its filling and further seasonal fluctuations in the volume of the reservoir (about 3 billion m³) on the seismic activity in the upper part of the crust, with an area of at least 1000 km². This was the reason for the occurrence of induced technogenic earthquakes in this area. The effect of induced seismicity can be dangerous if completion of the dam and creation of the reservoir coincide in time with the natural rhythm of ordinary seismogenesis. It also turned out that powerful shaking of the upper part of the crust during the Dagestan earthquake disrupted the oil production regime in Dagestan.