Izvestiya, Physics of the Solid Earth最新文献

Abstract—The hydrogeology of fault zones, especially at considerable depth, is perhaps a most underdeveloped field in earthquake source mechanics. This is due to both the lack of the data on the filtration characteristics of the geomaterial at large depths and to the complexity of the processes of mass transfer, fracture formation and healing under high temperatures and pressures. In this case, the strong influence of fluid on both the friction characteristics and the stress conditions in the vicinity of the slip zone is obvious. Fluids are carriers of dissolved matter and thermal energy, an effective catalyst for various types of metamorphic transformations. According to some models, fluid flows can be triggers for the initiation and arrest of seismogenic ruptures. The current trend in world seismology to constructing a complex computational model that adequately describes the processes of preparation, initiation, and arrest of various fault slip modes requires developing the ideas about fluid dynamics of seismogenic faults. This review considers the information on hydrogeology of fault zones obtained in recent years. Models and ideas involving field data, laboratory and field experiments and numerical calculations regarding the role of fluids at different stages of the seismic cycle are analyzed.

Abstract—Numerous publications have appeared in the literature describing a new seismo-electromagnetic effect—the appearance of magnetic pulses with a duration of 1–40 s, which are detected at distances up to ten thousand km a few minutes before earthquakes of even low magnitude. An assumption was made about the universality of the processes responsible for generation of pulsed precursors and the fundamental possibility of a short-term (a few minutes) warning of an approaching earthquake. In this article, the possibility of the occurrence of ultra-low-frequency pulses that precede seismic events with magnitudes M > 5.0 is studied based on the data from a network of induction magnetometers in the Far East. Pulsed disturbances occur regularly in the records by these highly sensitive magnetometers. Some pulses are observed synchronously at several stations, which excludes their origin from local noise. The spectral maximum of about 7–8 Hz of the oscillatory structure, which appears in many pulses, corresponds to the fundamental frequency of the Schumann resonator. A comparison of magnetic observations with data from the World Wide Lightning Location Network (WWLLN) showed that some of the pulses were caused by lightning discharges in the 650 km vicinity of magnetic station. Although some of the impulses are observed immediately before earthquakes, their connection with seismic activity cannot be claimed with certainty. The calculation of the number of pulses within the 5-min interval before and after the seismic shock shows that they are randomly distributed around the time of the earthquake. Apparently, the pulses are mainly due to the ionospheric response to a distant lightning discharge.

Abstract—Ground-based magnetometers and vertical ionospheric sounding stations were used to record specific variations in the geomagnetic field, caused by the perturbation in the lower ionospheric current systems, and specific variations in the upper ionospheric electron density after a strong volcanic eruption in Kamchatka, Russia, on April 10, 2023. The analysis of the measurements from two series of explosions has shown that the impact on the lower ionosphere is realized via both seismic Rayleigh waves (which are a source of acoustic waves propagating into the ionosphere), and atmospheric internal gravity waves generated by explosions. At distances up to a thousand km from the source, a repeatability of the pattern of ionospheric perturbations after each of the six volcanic explosions is discovered. At larger distances, signals from acoustic waves caused by the Rayleigh waves are clearly recorded in the ionosphere, whereas separation of the signals from atmospheric internal waves is difficult due to the influence of perturbations from other external sources.

Abstract—It is generally recognized that the formation of the fold-and-thrust tectonic structures of mobile belts on continents is associated with crushing and narrowing of the Earth’s crust due to collision of lithospheric plates. The deformation of the Caucasian lithosphere in the recent time is generally consistent with these ideas. However, the block differentiation of the Caucasian lithosphere brings specificity into the directionality of recent vertical and horizontal movements. In this paper, we analyze vertical movements of the Caucasus estimated by means of high-precision leveling over a period of more than a century and consider their spatial correlation with the tectonics, seismicity, stress-strain state, and geophysical fields. A clear correlation indicating the deep tectonic nature of the long-term uplifts of the Caucasus crust is revealed. The differentiation of the Arabian plate movement causes partitioning of the Caucasus territory into provinces that differ by the pattern of recent movements, orientation of faults, and stress-strain state of the geomaterial. These provinces also have distinctions in seismicity in terms of the number of seismic events and focal mechanisms of the earthquakes. We propose a model of a deformation mechanism of the Greater Caucasus, which accommodates the long-term trend of the Caucasus uplift in the conditions of general shortening of the Earth’s crust. The results of the analysis provide a basis for discussion of a probable mechanism of neotectonic evolution of the Greater Caucasus, which can be used in the seismic hazard assessment of the North Caucasus.

Abstract—The generalized cellular model based on the of Olami‒Feder‒Christensen cellular automaton model and modified by considering the durability of the material based on the kinetic concept of the strength of solids developed by Academician S.N. Zhurkov is used to model and clarify the nature of the statistical law of earthquake productivity. The modified model is named Olami‒Feder‒Christensen‒Zhurkov (OFCZ) model. The OFCZ model captures the main statistical regularities and patterns of seismicity: the Gutenberg‒Richter and Omori‒Utsu laws, the Bath’s law, fractal geometry of seismicity, and the law of earthquake productivity. It is shown that the clustering of model events (analogs of earthquakes), corresponding to the earthquake productivity law, is caused by the kinetic component of the OFCZ model. The dependences of productivity on material strength and temperature of the medium are obtained. The influence of the Zhurkov parameter and the cell transmission (coupling) parameter in the cellular model (dissipativity of the model) on the productivity is considered. It is shown that the revealed dependences of productivity on strength and temperature are consistent with the empirical data.

Abstract—A collection of igneous rocks of the Ukrainian Shield sampled from the Korsun-Novomyrhorod pluton (age interval 1760–1735 Ma, Ingul Domain) and from the Korosten pluton (age 1760–1750 Ma, North-Western Domain) is studied. The magnetic and thermomagnetic properties of samples were studied and X-ray diffraction analyses were carried out to obtain reliable determinations of paleointensity (B_anc), It is shown that the carriers of the characteristic component of natural remanent magnetization are single- and small pseudo-single-domain magnetite grains. B_anc was determined by two methods: through the Thellier‒Coe procedure with pTRM checks and by Wilson method. Paleointensity determinations are obtained from five sites and shown to meet quality criteria. For all sites, B_anc and the virtual dipole moment (VDM) values are extremely low, varying within the ranges 3.6–9.76 μT and (0.92–2.43) × 10²² Am², respectively. The analysis of the data from the paleointensity world database (WDB) indicates that the geodynamo operation mode in the Proterozoic can be characterized by an alternation of strong and weak dipole regimes, but the validity of this conclusion entirely depends on the reliability of data reported in the literature and presented in the WDB.

Abstract—We analyze the postseismic processes in the region of the M_w 8.2 Chignik earthquake, Alaska, which occurred on July 29, 2021. Using the model of the seismic rupture surface constructed in our previous work (Konvisar et al., 2023), we have modeled the viscoelastic relaxation process. The results indicate that by reducing the viscosity of the asthenosphere to 10¹⁸ Pa s we an achieve the displacement velocities that are close to those recorded at the coastal GPS sites. However, the displacements on the islands near the source zone of the earthquake differ significantly not only in magnitude but also in direction. At the same time, the constructed postseismic creep (afterslip) model agrees well with displacement data at the GPS sites and with the line-of-sight (LOS) displacement map derived from radar images taken from the descending orbit of the Sentinel-1A satellite. We also analyze temporal variations of gravity field in the earthquake region. The obtained coseismic anomaly is consistent with the anomaly calculated from the rupture surface model. Isolating the postseismic anomaly it is not yet possible due to the insufficiently long time series of gravity models for the time period after the earthquake. The analysis of the postseismic processes is continued in the second part of this work (Smirnov et al., 2024), where we compare development over time of the postseismic displacements of various GPS sites with the aftershock activity, which allows us to draw conclusions about the creep nature of the postseismic processes in the source region of the Chignik earthquake.

Abstract—The paper presents the results of rock magnetic studies and relative paleointensity determinations from sediments of Lake Shira, Khakassia. Carrier minerals of natural remanent magnetization (NRM) were identified through hysteresis loop parameter measurements, thermomagnetic and X-ray diffraction (XRD) analyses. The sediment age was determined by radiocarbon dating; according to age estimates, the studied sediment sequence covers approximately the past 9100 years. To obtain high-quality relative paleointensity results, the determinations were made on linear segments of the pseudo-Arai‒Nagata diagrams. The quality was assessed by the criteria of the number of points in the calculations of slope, quality criterion (q), NRM fraction destroyed in the paleointensity determination interval, and relative paleointensity determination error (σ). According to the rock magnetic studies and XRD analysis, the magnetic carriers are mainly single-domain (SD) and pseudo-single-domain (PSD) magnetite and hematite. The comparison of the obtained relative paleointensity data with model paleointensities calculated for the Shira coordinates from the various models (CALS10K.1b (Korte et al., 2011), PFM9k.1 (Nilsson et al., 2014), HFM.OL1.AL1, CALS10k.2 ARCH10k.1 (Constable et al., 2016)), with absolute paleointensities and with the collection of results from the studies of sedimentary and igneous rocks and archaeomagnetic objects has shown that these data are in good agreement and share common trends. This provides grounds for applying this approach to paleointensity determination from bottom sediments of modern lakes using the pseudo-Thellier method.

Abstract—The collection of paleomagnetic samples of the Lower Devonian Frænkelryggen Formation from the northwest of Spitsbergen is studied. The main carrier of the natural remanent magnetization of the studied rocks is hematite. Based on the component analysis results, the prefolding, bipolar components of the natural remanent magnetization with a positive reversal test are identified. The sequence of the magnetozones of the studied section is compared with the existing world data for Lower Devonian.

Abstract—Dynamic exploration and development of the Arctic zone of the Russian Federation is inextricably linked to the need to minimize risks to the technosphere, associated, among other things, with space weather effects on power equipment systems operated within the coverage of the auroral oval. At the same time, the concomitant monitoring of space weather parameters and variations of the geomagnetic field in the Arctic is carried out only by means of a small group of satellites and several dozens of magnetic stations located mainly in the USA, Canada, northern and central Europe. It is clear that the current situation practically excludes the possibility of operational diagnostics of the level of geomagnetically induced currents (GIC) for the most part of the Arctic zone of the Russian Federation, where, in fact, the only available indicator of space weather conditions are polar auroras. The paper proposes an approach to interpreting aurora appearance to assess space weather impact on high-latitude infrastructure facilities. Based on the case study of the “Vykhodnoy” substation of the “Severnyi Tranzit” (Northern Transit) main electric transmission line it is shown that when the aurora is observed in the north, at the zenith (overhead), and in the south relative to the observation point, the most probable (30-min average) GIC is 0.08, 0.23, and 0.68 A, respectively. At the same time, the probability of half-hourly average GIC exceeding 2 A (with auroras observed in the north, overhead, and in the south relative to the impacted object) is ~6, ~10, and ~15%, respectively. Finally, the ways to improving the proposed technique and the applicability limits of the approach are discussed.