Problems of Engineering Seismology: article

Dagestan earthquake of 1970: A look half a century later
A.A. Lukk A.Ya. Sidorin
Schmidt Institute of Physics of the Earth, Russian Academy of Sciences
Journal: Problems of Engineering Seismology
Tome: 49
Number: 4
Year: 2022
Pages: 140-154
UDK: 550.34
DOI: 10.21455/VIS2022.4-10
Keywords: Dagestan earthquake, earthquake parameters, isoseist map, aftershocks, destruction, damage, seismic hazard, Dagestan wedge, Chirkeyskaya HPP, oil production
Аnnotation: In connection with the 50th anniversary of the devastating 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, and the most important is that it was the strongest instrumentally recorded earthquake in the Caucasus at that time, and the nearest seismic station “Makhachkala” was located 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 focus was built by S.S. Arefiev et al. [2004] based on data on the inversion of body waves from this earthquake. According to this model, the focus of the Dagestan earthquake was multiple and consisted of three subsources. The initial rupture (subsource) with a horizontal extent of 14 km was located in the center of the source zone at a depth of 9 km. The second rupture began about 2 s later, it was located 10 km east of the first one at a depth of about 10 km and had a horizontal extent of 20 km. The third subsource arose 10 km west of the first one at a depth of 12 km. The Dagestan earthquake made it possible to significantly refine the estimates of the seismic hazard of the region. This was extremely important in connection with the construction of the Chirkey hydroelectric power station with a high-altitude dam (232 m) in the zone of 8 intensity shaking of this seismic event. The creation of the reservoir itself during the construction of a high-pressure concrete dam of a hydroelectric power station led to the manifestation of the influence of its filling and further seasonal fluctuations in the mass of the reservoir (about 3 billion m3) on the seismic activity of the upper part of the Earth’s crust with an area of at least 1000 km2. This was the reason for the occurrence of induced man-made earthquakes in this area. The presence of the effect of induced seismicity can be dangerous if the completion of the construction of the dam and the creation of a reservoir with it coincide in time with the natural rhythm of ordinary seismic generation. It also turned out that powerful shaking of the upper part of the Earth’s crust during the Dagestan earthquake led to a violation of the oil production regime in Dagestan.