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No 6 (2025)
Articles
NDC-Type Tectonic Earthquakes in Subduction Zones of the Northwestern Part of the Pacific Seismic Belt
Abstract
A systematic analysis of seismic moment tensors of earthquakes in the subduction zones of the Aleutian, KurilKamchatka and Japanese island arcs was carried out. A method for identifying earthquakes with foci that donot satisfy the double dipole model (NDC-type earthquakes) is applied, based on estimating the angle between the slip vector and the rupture plane in the earthquake focus using data on the seismic moment tensor main values. A study of the error distribution in the estimates of the moment tensor components made it possible to identify earthquakes with a significant NDC component of the focus. Some distribution features of such earthquakes in the studied region are discussed. Comparison of the results of identifying foci with a significant NDC component according to data from various seismological agencies showed that the absolute values of the angle between the slip vector and the rupture plane were somewhat underestimated in the catalogs of theUS Geological Survey (NEIC) and the Japanese Institute of Earth Sciences (NIED) compared to the Global Centroid Moment Catalog (GCMT). The applied method and the obtained estimates of the NDC component of slip in earthquake foci can be used in numerical modeling of movements in the foci of strong earthquakes using a set of groundbased and satellite deformometric data.
Izvestiya, Physics of the Solid Earth. 2025;(6):3-17
3-17
Aftershock Features of Mw6.6 Vilyuchinsk Earthquake on April 03, 2023 (Kamchatka)
Abstract
The article analyzes the aftershock activation observed in the south of Avacha Bay (Kamchatka) as a result of the Vilyuchinsk earthquake on April 03, 2023 MW = 6.6 (j = 52.58°N, l = 158.78°E, h = 105 km). The total duration of this activation is estimated at 450 days. The linear dimensions of the studied area are limited horizontally by an ellipse with axes a = 34 km (azimuth a = 117°), b = 22 km, in the depth range h = 95-105 km. The orientation of the ellipse corresponds to one of the two nodal planes of the main event mechanism. Two stages in the attenuation of the aftershock flow were distinguished: 1) in accordance with the Omori law and with a duration of 8.4 days; 2) with exponential (t = 140 days) attenuation until reaching the background seismicity level. In terms of the number of earthquakes, the two stages are comparable. The phase of regime change corresponds in time to the interval between the strongest aftershocks — April 11, 2023 ML5.5 and April 21, 2023 ML4.9. It is shown that these two earthquakes are a doublet based on the high correlation of waveforms and the proximity of their epicenters. A sharp postseismic decrease in the slope of the Gutenberg-Richter graph bby 1.5 times after the strongest aftershock on April 11, 2023 ML5.5 is shown, with subsequent recovery throughout the exponential aftershock regime. No variations were detected in the bparameter in the Omori regime.
Izvestiya, Physics of the Solid Earth. 2025;(6):18-32
18-32
Automation of Processing Large Volumes of Seismological Data when Studying Seismicity of the Khubsugul Region for 2014-2016
Abstract
This work uses open data of an international experiment in Central Mongolia, in particular, data from temporary stations installed in the area of Lake Khubsugul. This network consisted of 26 stations and operated in 2014-2016. This time interval includes an interesting to consider, fairly large event with an aftershock process, which occurred directly under Lake Khubsugul on December 5, 2014, with magnitude ML = 5.2. Event detection and location is performed automatically using a publicly availableAI-based detector, EqTransformer, designed simultaneously to detect earthquake signals and determine Pand Sphases from single station data records, a phase associator using grid search, and an event locator Hypoinverse, which is also open source software. The following results were obtained: the source area of the Khubsugul earthquake of 2014 has no contact with the source area of the Khubsugul earthquake of 2021 and is not connected with known faults in this area; at the level of weak earthquakes ML <2, increased activity is noted in the northern part of the Darkhad depression, as well as along the western side of the Khubsugul depression; from the west in the seismicity structure, an increased number of earthquakes is noted not only in the Busingol and Belin depressions, but also in the internal regions of the Shishkhid Highlands; during the experiment, there were no earthquakes in the area of the focal zone of the Khubsugul earthquake of 2021 and in the area of development of the Darkhad earthquake swarm in 2022 — 2023.
Izvestiya, Physics of the Solid Earth. 2025;(6):33-47
33-47
Analytical Calculation of the Seismic Hazard Curve from the Source Zone
Abstract
A number of specialized software packages have been now developed to calculate seismic hazard curves. Their algorithmic basis is based on the use of numerical methods. The key feature of such calculations is the discretization of the selected areas of seismic source zone (SSZ) — each zone is divided into finite elements, and each element has seismic activity proportional to its area. Besides, the values of earthquake magnitudes in the calculations also take a discrete set of values. Numerical methods certainly open upthe possibility of solving problems that cannot be described analytically, but they also introduce certain errors. Too large a division may not take into account local features of the seismic regime. The accuracy of the final results depends significantly on two key parameters: the selected magnitude discretization step and the principles of dividing the SSZ zones. In this study, weconsider a localized seismic source whose event flow strictly corresponds to the GutenbergRichter law. To determine the intensity of seismic vibrations, the Shebalin macroseismic field equation is used.
Izvestiya, Physics of the Solid Earth. 2025;(6):48-56
48-56
Modeling of Seismological Temperature Forecast at Depths of the Upper Crust
Abstract
The accuracy of deep temperature forecast based on seismic wave velocity data and model thermograms was investigated depending on the distance to the forecast point. For this purpose, the results of seismic tomography along the sublatitudinal profile of the Northern Tien Shan subsurface area were used, as well as the temperature model previously constructed for this profile to a depth of 27 km. An assessment of the temperature forecast accuracy using artificial neural networks showed that at distances to the forecast point of upto 16 km, the discrepancies between the forecast and model temperature values based on longitudinal and transverse wave velocities, as well as their combination, are 7.4, 5.7 and 4.6%, respectively. With a 4-fold increase in the distance to the forecast point, they increase by 2-3 times. In general, it can be concluded that neural network temperature forecast of the earth’sinterior based on seismic wave velocity data can be performed with acceptable accuracy at large distances from the initial data measurement points and serve as a “seismological geothermometer”.
Izvestiya, Physics of the Solid Earth. 2025;(6):57-65
57-65
The Earth’s Crust of the Western Orenburg Region According to the Receiver Function Data
Abstract
The properties of the Earth’scrust of the western Orenburg region are discussed. The data analysis of the broadband seismic station ORR (Orenburg), which is part of the “Neftegaz-Seismika” network, was carried out using the receiver function method. The Zhu-Kanamori method was used to estimate the average parameters of the crust — the thickness and the ratio of the longitudinal and transverse velocities of seismic waves — within the framework of a single-layer model. A one-dimensional section of seismic wave velocities under the station was obtained by inversion of the waveforms of the receiver function. It is shown that the upper part of the constructed section is characterized by low values of transverse wave velocities. This is consistent with the presence of terrigenous and oil- and gas-containing rocks under the seismic station. The obtained section, in general, does not contradict the interpretation results of two DSS profiles performed in this region, except that the crustal thickness calculated by the receiver function method and approximately equal to 35–37 kmturns out to be 7–10 kmless compared to the DSS results. In order to make a final conclusion about the crustal thickness in the region, additional research on observations of a larger number of broadband seismic stations is required.
Izvestiya, Physics of the Solid Earth. 2025;(6):66-74
66-74
Satellite Gradiometer: Principles of Measuring the Earth’s Gravitational Field
Abstract
The paper presents the principles of measuring the Earth’sglobal gravitational field (EGF) using a spacecraft (SC) equipped with a high-precision three-axis gravity gradiometer and located in low Earth orbit. Such a spacecraft is primarily designed to measure high-frequency EGF harmonics. Gradiometer measurements are not sensitive to low-order EGF harmonics, so to reconstruct the EGF in the entire frequency range, starting from n=2, high-precision measurements of the SCorbit are required, which are performed by the onboard high-precision GNSS receiver. Theoretical aspects of satellite gradiometry are considered and the problem of reconstructing the EGF harmonics is solved based on model measurements. To calculate the “measured” components of the gravitational potential tensor, the EGM2008 EGF model was used. A program for numerical integration of the spacecraft orbit was also developed based on this model, including additional forces acting on the spacecraft. A direct method is used to reconstruct the EGF: a matrix of conditional equations is compiled relative to the Stokes coefficients. Solving this system using the least squares method allowsus to obtain corrections to the harmonics of the a priori (initial) EGF model, which used the EGM96 model. This way, the harmonics of the reconstructed field are formed. The quality criterion for the solution is the agreement between the difference in the amplitudes of the harmonics of the reconstructed model and the EGM2008 model. Based on the obtained model solutions, an optimal SCorbit was selected for carrying out gradiometric measurements, and estimates of the accuracy characteristics of the main key elements of the spacecraft onboard scientific instruments were obtained.
Izvestiya, Physics of the Solid Earth. 2025;(6):75-104
75-104
Creation of Maps of Earth’s Gravitational Field Parameters Using Data from Joint Measurements of Astrometer and Gravimeter
Abstract
The article is devoted to the creation of maps of the Earth’sgravitational field parameters using the measurement data of a gravimetric complex, including an astrometer of the plumb line deviation and a high-precision relative gravimeter. Conducting joint area measurements using the complex allows determining the following Earth’sgravitational field parameters: acceleration of gravity and gravity anomalies, components and the total value of the plumb line deviation, components of acceleration of gravity and gravitational gradients (second derivatives of the anomalous potential). The total measurement time at a single point using the complex does not exceed 1 hour, the standard deviation of the measurement series of the plumb line deviation components is from 0.1″ to 0.3″, the acceleration of gravity is 10 μGal. The paper presents examples of maps of the above-mentioned Earth’sgravitational field parameters, created based on the measurement results using the gravimetric complex in the Moscow region, including the measurement profile across the gravitational-anomalous Moscow attraction.
Izvestiya, Physics of the Solid Earth. 2025;(6):105-112
105-112
Spectral Properties of the Magnetic Field During the Matuyama-Brunhes Inversion
Abstract
It is shown that, according to observations, during the last geomagnetic field inversion, there was a decrease in the amplitude of four axisymmetric harmonics in the expansion of the magnetic field in spherical functions. Only the dipole component changed sign at the moment of reversal. For all four modes, quasi-variations with characteristic times of 10–50 thousand years were observed over an interval of 200 thousand years. During the reversal, there was an increase in magnetic field variations with characteristic times of 100–1000 years, caused by the destabilization of hydrodynamic flows in the core.
Izvestiya, Physics of the Solid Earth. 2025;(6):113-119
113-119
Comparative Analysis of the Magnetic Field Archeointensity Recorded in the Brick Fragments From a Roman Kiln (Dragovishtitsa Village, Western Bulgaria)
Abstract
This paper is devoted to the study of the features of thermoremanent magnetization (TRM) acquisition in brick fragments from a Roman kiln, uncovered by archaeological excavations in the vicinity of the village of Dragovishtitsa (Western Bulgaria), in experiments using the Thellier method as modified by Coe. The aim was to determine the magnitude of the geomagnetic field in ~300 AD. Initially, petromagnetic and archeomagnetic studies were carried out in the Paleomagnetic Laboratory of the National Institute of Geophysics, Geodesy and Geography of the Bulgarian Academy of Sciences. Then, experiments using the Thellier-Coe procedure at two cooling rates of samples taking into account the TRM anisotropy were carried out in the Laboratory of the Main Geomagnetic Field and Petromagnetism of the Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences. Based on 18 archaeointensity determinations, the average weighted value of the magnetic field Bav= 56.5±0.8 μTwas obtained, corresponding to the archaeological age of 260±20 CE. The dating of 281-342 CEobtained by the archaeomagnetic method is consistent with the archaeological estimate of the kiln operation time. The calculated value of archaeointensity is in satisfactory agreement with the reference values of the magnetic field for Bulgaria and confirms its decrease in the time interval of ~200-300 CE.
Izvestiya, Physics of the Solid Earth. 2025;(6):120-141
120-141
Results of rockmagnetic and paleomagnetic studies of Devonian deposits of the Pavlovsky quarry (Voronezh region)
Abstract
Wepresent the results of magneto-mineralogical and paleomagnetic studies of the Middle and Upper Devonian section of the Pavlovsky quarry located in the Central Devonian field of the East European Platform. The magneto-mineralogical composition of the studied deposits is complex, withup to 4-6 magnetic phases recorded in them. The section is subdivided into several zones by magnetic mineralogy and by the observed characteristic components of natural remanent magnetization, however, the boundaries of zones donot coincide with each other. Two interpretable characteristic components are distinguished in the section. The bipolar Devonian component DE+DWrev and the anomalous componentS1-2-3-4 , which paleomagnetic poles are consistent with the poles of a number of sections of Devonian rocks of the East European Platform.
Izvestiya, Physics of the Solid Earth. 2025;(6):142-163
142-163
Test of Conglomerates in the Katav Formation of the Neoproterozoic (Southern Urals)
Abstract
In order to prove the synchronicity of magnetization to the Formation of rocks of the Neoproterozoic Katav Formation (Southern Urals), a paleomagnetic conglomerate test was performed. Samples of breccias from two sections of the carbonate Katav formation located in the vicinity of Tolparovo and Katav-Ivanovsk were studied. Petrographic and electron microscopic studies of thin sections and polished sections have been carried out, confirming the similarity of the mineral composition in the fragments and matrix. The qualitative assessment of the chaotic directions of magnetization of the fragments according to Graham was verified by more stringent Rayleigh and Hodges-Ajne criteria. The results allowus to state that the conglomerate test is positive, and the high-temperature magnetization component in the rocks of the Katav Formation is primary.
Izvestiya, Physics of the Solid Earth. 2025;(6):164-178
164-178
Simultaneous Observations of Gamma Background of Soil Radionuclides and Electrical Conductivity of the Surface Atmosphere
Abstract
The paper presents the results of simultaneous ground-based observations of gamma-ray spectra from soil radionuclides, volumetric radon activity, and electrical conductivity of the air in the surface atmosphere. Based on the analysis of gamma-ray spectra, the concentrations of 238 U, 232 Thand 40 Kin the upper soil layer and the terrestrial gamma-ray dose rate were estimated for 43 sites at 8 observation points, the distance between which ranges from 1 mto 25 km. The range of recorded concentrations was 1.28-2.64 mg/kgfor 40 K, 0.7-1.41 mg/kgfor 238 U, and 4.4-8.88 mg/kgfor 232 Th. The average ratios between the volumetric activities of the specified soil radionuclides and statistics of deviations from the averages were determined. During the observation period, the range of gamma-ray dose rate variation from soil radionuclides at a height of 1 mabove the earth′ssurface was 26-52 nGy/h. During the rain, an increase in the number of gamma-quanta in the 214 Bipeaks is recorded, reaching 1200% for the quanta energy near 1765 keV and 300% for the quanta energy near 2204 keV. The autocorrelation function of the time series of gamma-ray dose rate from soil radionuclides in good weather conditions decreases with a characteristic time scale of several days, which decreases to several hours in the presence of precipitation in the analyzed time interval, accompanied by an increase in the 214 Bilines in the gamma-ray spectrum. The electrical conductivity of the air of the surface atmosphere shows the presence of a diurnal variation with a minimum in the daytime and two maxima — in the morning and evening. Observations distributed by height showed that the electrical conductivity at a height of 0.5 mis on average greater than at a height of 1.5 m, while in the daytime the difference in conductivity values at these heights is expressed more clearly.
Izvestiya, Physics of the Solid Earth. 2025;(6):179-192
179-192
Mobile Impulse Electromagnetic Soundings. Assessment of the Possibilities of Using UAVs
Abstract
On the example of transient electromagnetic sounding (TEM) of moraine deposits the efficiency of the TEM-FAST technology is demonstrated. This technology uses a compact 25 m × 12.5 mcombined transmitterreceiver antenna for measuring transient responses in the microsecond range. The research depth with specific resistance of sandy-clayey deposits of 30–300 Ohm·mis notless than 50 mwith a “dead” zone thickness of not more than 6 m. For mobile pedestrian sounding, an antenna fixed on 4 flexible poles at a height of 2.5 mabove the earth′ssurface was used. The measuring system, with a total mass of 2.5 kg, was transported along the profiles by a team of 4 people at a speed of ~1 m/s. Every 20 seconds after processing 13,000 pulses, the system in the “autopilot” mode recorded the measurement results and coordinates. The repetition rate of current pulses with an amplitude of I = 3.3Аwasf = 3.2 kHz, the measured range of transient response timest = 4 — 64 μs. Vibration noises arising during movement due to deformations of the antenna contour in the Earth′smagnetic field reduced the sounding depth to 50–60 m. Based on the area sounding data, 3D geoelectric model of the territory was constructed, which was used to assess the capabilities of the TEM-FAST system in flight mode. Transient responses were synthesized, corresponding to different antenna heights above the surface of the studied environment. Despite the decrease in response amplitudes when raising the antennas to a 30 mheight, the sounding depth remained within 50 m. Based on mass-produced light UAVs (unmanned aerial vehicles) equipped with real-time dynamic positioning systems, it is proposed to tow the TEM system with a convoy of devices flying or hovering above the earth′ssurface in autopilot mode. When positioning antenna angles with decimeter accuracy, the noise threshold of transient response measurements will not exceed the levels obtained during mobile pedestrian sounding, and the research depth will not fall below 50 m.
Izvestiya, Physics of the Solid Earth. 2025;(6):193-206
193-206