№ 6 (2025)

The article describes the updating and actualization of the earthquake catalog of the Arctic zone of the Russian Federation (AZRF), which combines all available data from Russian and international seismological agencies, bringing the magnitudes to a homogeneous scale. The first version of the catalog was presented in 2022–2023. The catalog of the Eastern Sector of the Russian Arctic contained data till 2020, and the Western Sector and territories of the Arctic Ocean till 2022. Since then, a significant amount of new data has accumulated: the collections “Earthquakes of Russia” have been extended until 2023, “Earthquakes of Northern Eurasia” – until 2021, and the catalog of the International Seismological Center (ISC) – to the present. Due to different network configurations and record processing methods, agencies may register/skip different events. For this reason, combining earthquake data from various seismological agencies makes it possible to obtain the most comprehensive catalog for the region under study. When combining earthquake catalogs, the problem arises of identifying and deleting duplicates (records related to the same seismic event). To solve this problem, this paper uses a new fully automated version of the modified nearest neighbor method based on the analysis of the metric distribution in the network error space when determining epicenters and times of seismic events. The unification of magnitude estimates is based on a regression analysis of different types of magnitudes performed during the creation of the first version of the combined catalog. The updated catalog contains 53 777 earthquakes.

The paper presents the results of the analysis of macroseismic and instrumental data of the earthquake that occurred on April 3, 2023 at 03:06 UTC in the southern part of the Avacha Gulf (Kamchatka) at a depth of ~105 km. This earthquake was named “Vilyuchinsk earthquake” – its epicenter was located 47 km from Vilyuchinsk town. It was felt in the range of epicentral distances Δ up to 555 km. Maximum shaking with intensity I = 5–6 was recorded at four locations (Δ = 40−62 km), including Petropavlovsk-Kamchatsky and Vilyuchinsk. Peak ground motion accelerations exceeded 20 cm/s² on records from 23 digital accelerograms (Δ <101 km). This earthquake was accompanied by a series of aftershocks lasting about 400 days. Estimates of the dimensions of the main shock source (~23 km × 15 km) were obtained from the size of the aftershock area. Waveforms from regional seismic stations were used to determine the basic source parameters of the main event and its strongest aftershock: moment magnitudes M_w (6.6/4.9), depths of the equivalent point source h_e (95/110 km), and focal mechanisms. The compressional axes of both mechanisms are oriented approximately along the dip of the subduction zone. Many earthquakes in the vicinity of the Vilyuchinsk earthquake have similar focal mechanisms. It can be assumed that the upper layer of the subducting plate, to which the source of the Vilyuchinsk earthquake belongs, is in a state of compression in the direction of the dip of the plate. The earthquake was preceded by anomalous variations of a number of seismological, hydrogeochemical, hydrogeodynamic, geoacoustic and electromagnetic parameters. In 4 cases, the anomalies detected in real time were used to successfully predict the location, time and magnitude of the expected event. Postseismic variations of groundwater flow rate and mineralization with a duration of ~260 days were detected at one of the Pinachevsky springs (Δ ~80 km).

Common features of the relief of the Nevado del Ruiz and Elbrus volcanoes have been revealed, which can be largely explained by the similarity of the geodynamic regimes of these volcanic centers. The established general patterns of orientation of lineaments, watercourses, elongation lines, configuration of ring elements of interpretation, as well as the modern seismic regime of the studied areas complement the ideas about the deep structure and state of magmatic feeding systems, emphasizing the need to control the nature of weak seismicity in the immediate vicinity of the Elbrus volcanic structure to clarify its volcanic hazard.