Izvestiya, Physics of the Solid Earth最新文献

Abstract—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.

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.

Abstract—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.

Abstract—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.

This paper examines the response in geomagnetic-field variations caused by the 2020–2023 earthquakes with magnitudes Mw ≥ 7.0 in the Aegean Sea and eastern Turkey. A detailed comparison of high-precision observations of the geomagnetic field and seismograms recorded at complex geophysical observatories within a radius of 3000 km from the epicenters was carried out. The joint analysis involves averaged 1-s data on the rate of change of the magnetic field and records from broadband seismic stations. Their characteristics are assessed in both in time and frequency domains. The spectral characteristics of body and surface waves are separately compared with those of the geomagnetic signal. It is shown that the beginning of disturbance in the magnetic field at each observatory strictly coincides with the arrival of the P-wave and intensifies with the arrival of S-waves. The maximum geomagnetic disturbance is caused by surface waves. The amplitude of electromagnetic excitations is proportional to the amplitude of the parent seismic phases. Thus, the coseismic nature of the observed electromagnetic signal has been confirmed, suggesting its excitation in the Earth’s crust as seismic waves propagate.

The article presents analysis of macroseismic data on the September 21, 2020 (M_w = 5.6) Bystraya earthquake, which occurred in the eastern part of the Tunka basins system on the southwestern flank of the Baikal rift zone. Macroseismic data were collected mainly through an Internet questionnaire posted on the website of the Baikal Branch of the Geophysical Survey, Russian Academy Sciences. A total of 3013 eyewitness responses were collected, which is currently an unprecedented number in the entire history of macroseismic observations in the Baikal region. In total, we collected data for 263 Intensity Data Points. The maximal shaking intensity (VI–VII MSK-64) was observed in the Bystraya village and the Kultuk settlement. The shaking intensity V MSK-64 was noted at a distance of up to ~180 km; intensity IV MSK-64 was recorded at a distance of up to ~550 km. Analysis of data on the Bystraya earthquake revealed significantly lower attenuation compared to that expected from the regional macroseismic equation. Due to the large volume of macroseismic data collected, as well as the high efficiency of the data collection method used, the Bystraya earthquake can be considered an important milestone in macroseismic research in East Siberia.

This paper verifies the compliance of the earthquake productivity law (Shebalin et al., 2020a) in laboratory experiments on rock destruction. Westerly granite and Benheim sandstone specimens were subjected to uniaxial loading under uniform compression. An acoustic-emission (AE) recording system made it possible to create catalogues of AE sources similar to earthquake catalogues. The data from experiments conducted at the Rock Friction Laboratory (USGS, Menlo Park, United States) and the Geomechanics and Rheology Laboratory (GFZ, Potsdam) were analyzed. It was found that the AE events in the considered samples are characterized by a unimodal distribution of the nearest-neighbor proximity function. The compliance of the productivity law for acoustic-emission events in laboratory experiments on the destruction of rock samples is shown, which gives grounds to speak about the similarity of grouping processes in real seismicity and in laboratory conditions.

Abstract—The Altai–Sayan mountain-folded belt is analyzed with the purpose of (1) revealing peculiarities of localization of large-scale polymetallic mineralization in the lineament-block structure of the region and (2) determining the geophysical and geomorphic peculiarities of the locations of these deposits using the Cora-3 pattern recognition algorithm. The lineament-block structure of the region is determined using morphostructural zoning. A spatial correlation between large and superlarge polymetallic deposits and morphostructural nodes is revealed. Based on this correlation, a dichotomy problem is solved, which is to divide the entire set of nodes in the region into two classes—ore-bearing and non-ore bearing. For this purpose, we used the Cora-3 logical recognition algorithm with training, for which the input data are geomorphological and geophysical parameters of the nodes. The training set of the algorithm was composed of the nodes where large and superlarge polymetal deposits are known. At the training stage, the algorithm identified the sets of the characteristic features that are peculiar to each class. Based on these features, all the nodes in the region were divided into ore-bearing and non-ore-bearing ones. As a result of recognition, the nodes in which deposits of the considered types and sizes are known were classified as ore-bearing, and, in addition to them, another 11 nodes were identified that meet the features determined in the work and can be considered potentially ore-bearing.

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 1980 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 with 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 work is devoted to modeling and studying geodynamic processes occurring in the vicinity of focal zones of the strongest (M ≥ 8) subduction earthquakes at different stages of the seismic cycle based on satellite geodesy data. The processes of preparation and implementation of a number of powerful events that occurred in the Kuril–Kamchatka, Chilean, Japanese, and Aleutian subduction zones at the beginning of the 21st century were studied. Clear spatial relationships have been identified between geodynamic processes occurring at different stages of the seismic cycle. It is shown that structural inhomogeneities of the geoenvironment have a direct impact on the processes of accumulation and release of elastic stresses.