No 5 (2024)

The spatial clustering of epicenters of seismic events in the Northwest Pacific Ocean is analyzed using the Discrete Perfect Sets (DPS) topological filtering algorithm. The results of the analysis are presented in this paper. Based on the data shallow earthquakes recorded from 1963 to 2022 by the seismic network of the Kamchatka Branch of the Geophysical Survey of the Russian Academy of Sciences, stable areas of epicenter clustering are identified. These areas are associated with the Northern and Southern segments of the Kuril-Kamchatka seismofocal zone and do not depend on the time of recording of the earthquakes. The characteristic clustering radius for the Kuril-Kamchatka seismofocal zone is determined and is found to be 42–44 km. The analysis has confirmed the unique pattern of seismicity in the territory of the Commander segment of the Aleutian arc, which differs from that observed in the Northern and Southern segments.

This work constructs a seismic regime model for the eastern sector of the Arctic Zone of the Russian Federation (AZRF) based on a newly developed, comprehensive integral earthquake catalog for the region, using a uniform magnitude scale from 1982 to 2020. The model parameters are calculated using a novel high-contrast mean-position method, where values are determined within large-radius circles but are assigned to the mean position of epicenters. A quantitative verification method, the L-test, based on the likelihood function, demonstrates that the model aligns well with the initial data. The magnitude–frequency distribution reconstructed from the model corresponds well to observations, both in terms of slope and the number of earthquakes. The epicenters of the largest earthquakes (M ≥ 6) from both the 1982–2020 period and the 1900–1981 period, according to the Kondorskaya–Shebalin catalog, are located in areas with high expected recurrence of such earthquakes as calculated by the model.

The Gutenberg–Richter law establishes a log-linear relationship between the number of earthquakes that have occurred within some spatiotemporal volume and their magnitude. This similarity property presumably reflects fractal structure of the fault system in which earthquake sources are formed. The Gutenberg–Richter law plays a key role in the problems of seismic hazard and risk assessment. Using the Gutenberg–Richter relationship, we can estimate the average recurrence period of strong earthquakes from the recurrence rate of weaker earthquakes. Since the strongest earthquakes occur infrequently, with intervals of a few hundred years or more, it is not possible to directly assess their recurrence. From indirect geologic and paleoseismic estimates it often seems that strong earthquakes on individual faults occur more frequently than expected in accordance with the Gutenberg–Richter law. Such estimates underlie the hypothesis of the so called characteristic earthquakes. This hypothesis is in many cases additionally supported by the form of the magnitude–frequency distributions for individual faults, constructed from the data of modern earthquake catalogs. At the same time, an important factor affecting the form of the magnitude–frequency distribution is the choice of the spatial domain in which the distribution is constructed. This paper investigates the influence of this factor and determines the conditions under which the Gutenberg–Richter law is applicable for estimating the recurrence of strong earthquakes.

Previously conducted numerical studies of the influence of class X solar flares on seismic activity have shown that the absorption of X-ray radiation from a solar flare in the ionosphere can cause pulsations of the geomagnetic field up to 100 nT and the corresponding generation of telluric currents in faults in the Earth’s crust with a density of up to 10^–6 A/m², which is comparable to the current density created in the Earth’s crust by artificial pulse sources and leading to the initiation of weak earthquakes in the Pamirs and Northern Tien Shan. To verify these numerical results, an analysis was conducted of the possible impact of the 50 strongest class X flares (1997–2023) on both global seismic activity and earthquake-preparation zones located only on the illuminated part of the globe. The method of superimposing epochs has established an increase in number of earthquakes M ≥ 4.5 within 10 days after a solar flare, especially in the area with a radius of 5000 km around the subsolar point (up to 68% for flare class >X5), compared to the same period before it. Analysis of aftershock activity of the strong Sumatra–Andaman earthquake (M = 9.1, December 26, 2004) showed that the number of aftershocks with magnitude M ≥ 2.5 increased more than 17 times after the X10.1 class solar flare (January 20, 2005) with a delay of 7–8 days. In addition, it has been shown that solar flares of class X2.3 and M3.64, which occurred after the Darfield earthquake (M = 7.1, September 3, 2010, New Zealand), in the area of subsolar points of which the aftershock zone was located, probably caused three strong aftershocks (M6.3, M5.2, and M5.9) with the same delay of 6 days on the Port Hills fault, which is the most sensitive to external electromagnetic influences in terms of its electrical conductivity and orientation. Taking into account the concept of earthquake forecasting based on trigger effects proposed by G.A. Sobolev, the possibility is discussed of using the obtained results for short-term forecasting as additional information along with known precursors.

A new probabilistic approach to the problem of estimating the regional maximum possible magnitude and some parameters of seismic impact is proposed. The methodology of its practical application is described, which is based on considering the maximum magnitude in the future time interval T as a random quantity and using its quantile with a given level of confidence as the regional maximum magnitude.

The issue of the occurrence of seismicity induced by injection of fluid into the subsurface is considered. A model of nested fractures is presented, which allows simulating the process of fluid filtration in a rock containing fractures or faults, taking into account the change in the filtration properties of the latter during the change in pore pressure. The process of fault deformation is described using the displacement discontinuity method. The model is used to analyze the effect of fluid injection in the immediate vicinity of a fault on its subsequent deformation. The transition of fault slip from aseismic to seismic is investigated when the parameters of the friction law or fluid injection parameters change. Conditions have been found under which seismic slip may occur within the framework of the proposed model.

The article presents the general results of medium- and long-term forecasting of earthquakes with K ≥ 13 (M ≥ 5.0) in the Baikal rift zone. These results have recently been obtained through the joint use of the geoinformation system for predicting the preshock stage of earthquake preparation and its associated two-stage phenomenological model. This model was created based on the analysis of seismological data on the preparation of the most dangerous earthquakes that occurred in the Baikal rift zone. It is consistent with the results obtained in studies of seismic regimes of ice shock preparation on the Baikal ice cover and in conducting full-scale experiments on fault sections with the aim of clarifying physical and mechanical conditions for the emergence of the sources of seismic-induced oscillations.The paper provides an example of practical use of results obtained for earthquake forecasting, as well as the ways of refining seismic hazard assessments relative to the infrastructure in the city of Angarsk 100 km away from the seismically hazardous Main Sayan Fault (MSF), whose zone reveals a “locked” segment with a seismic gap during the seismic regime analysis. In accordance with its linear dimensioning which represents a length of 60 km, two L/M equations served as a basis for potential energy calculations whose maximum values correspond to M_max 7.1 and 7.8. It is shown that the use of the obtained earthquake-forecast results assists in refining the level of seismic hazard for the nearest time intervals of expected earthquakes with different Mmax values. Consideration is being given to the example of assessing the current seismic hazard using a medium-term forecast for the infrastructure of the city of Angarsk for the probability of seismic shaking from the southeastern section of the MSF zone for the next 10 and 50 years. The comparison with the OSR-16 map showed that the calculations carried out indicate a relatively lower level of seismic hazard for the city of Angarsk for 10- and 50-year expectation periods.

In this paper, we present a description of a database of earthquake focal mechanisms, which is compiled from the data of international seismological agencies and literature sources for the East Arctic region. It consists of 595 focal mechanism solutions for 273 seismic events with M = 2.1–7.6, which occurred in 1927–2022. Information about the source depth, the scalar seismic moment, and the moment magnitude are also presented there for many events. In addition to the focal parameters, their quality assessments are available, which facilitates a comparison of different solutions in many cases. For user convenience, the database has a graphical interface that permits searching by various attributes (coordinates, time, magnitude, and depth). In terms of volume of the collected information, our database significantly exceeds all the analogues available at the present time. It can be used to perform a seismotectonic analysis, to estimate the stress–strain state of the lithosphere, and to assess seismic hazard for the entire East Arctic region or its separate areas. Implementation of the compiled database for comparison of different solutions of earthquake focal mechanisms and their seismotectonic analysis is illustrated in the paper on the example of seismic events occurred in the Olenek Bay of the Laptev Sea and adjacent territories. We suggest adding new information to the database every five years in future.