Macroseismic and instrumental studies of the Verkhniy Fiagdon earthquake on January 26, 2020

Abstract

Relevance. The earthquakes study in the North Caucasus is not just an urgent task. Its solution is an urgent need. It requires daily, painstaking work to increase the comfort level of the population’s life. The aim of the work is to present a sufficiently detailed analysis of the tangible tectonic earthquake on January 26 at 21h 01m GMT, which occurred on the territory of the Republic of North Ossetia-Alania. Intensity of the shok equaled 4-5 in the epicenter. Research methods included: determination of the parameters of the seismic event hypocenter using the WSG and HYPO71 software complexes; description of the geological and tectonic position of the source; calculation and graphical presentation of the earthquake source mechanism by the signs of the first arrivals of P-waves; collection of macroseismic data by visits to the places of earthquake manifestation to determine the intensity of shaking the earth’s surface in points; consideration of historical and modern seismicity in the area of the investigated earthquake. As a result, the following solution of parameters of an earthquake is received: φ=42,69°N, =44,15°E, h=6 km, KР=11,2. The epicenter of the earthquake occurs near the Main ridge zone. In more detail, the earthquake happened in the seismotectonic block located between the Main Caucasian and Adaykom-Kazbek faults. For the earthquake, the mechanism of the focus was calculated according to the signs of the first arrivals of longitudinal P-waves at 20 stations. According to the solution, the earthquake occurred in the upper part of the earth’s crust under the action of compressive stresses, the type of motion is upthrust-strike-slip, which is consistent with the kinematic characteristic of the Main Ridge Zone. The earthquake, called Verkhniy Fiagdon earthquake, is characterized by the absence of a noticeable aftershock process, but the analysis of the available wave forms of the nearest seismic station showed the presence of a sequence of weak seismic events. The macroseismic effect of the earthquake was investigated in 25 settlements by the staff of the North Ossetian branch of the Geophysical Survey of the Russian Academy of Sciences. According to the survey results, the maximum intensity of concussions was 4-5 points. A map of earthquake manifestations in localities constructed based on the results of the intensity assessment. The history of seismicity of the focal zone of the investigated earthquake for the last 150 years is studied.