Fizika zemli

The generalized cellular model based on the of Olami‒Feder‒Christensen cellular automaton model and modified by the allowance for the lifetime of the material on the basis of the kinetic concept for strength of solids 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 model (OFCZ). The OFCZ model implements the main statistical regularities 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 law of earthquake productivity, is due to the kinetic component of the OFCZ model. The productivity dependences on material strength and medium temperature are obtained. The influence of the Zhurkov parameter and the cell coupling parameter in the cellular model (the 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.

The key parameters of an earthquake are magnitude, epicenter coordinates, and depth. Depth often has a decisive influence on the macroseismic effect of certain earthquakes. In this regard, for example, to assess seismic risk, one should know information on the statistics of earthquake occurrence at certain depths. In this work, catalogs of continental crustal earthquakes in the Southern Siberia are analyzed. The distributions of earthquake depths are approximated by various functions. The Weibull distribution, with a maximum at 8 km, is shown to describe the depth distribution of these crustal earthquakes most accurately. When the western (Altai–Sayan) and eastern (Baikal Rift Zone) parts of the region are considered separately, the Weibull distribution is also preferable. The maximum of the distribution is found to be at 9 km for the Baikal rift zone and at 7 km for the Altai–Sayan zone.

A source of a strong earthquake, as a rule, consists of subsources which are identified by waveform modeling. The modeling does not yield an unambiguous result. In this paper, we present an example when two significantly different focal mechanism solutions are published for the same earthquake: in one solution, the subsources are characterized by a similar type of faulting, while in the other solution, the last subsource has an opposite mechanism. In (Vakarchuk et al., 2013), this discrepancy was interpreted by the realization of a compensatory motion. The compensatory movements are detected not only in the subsources but also at the scale level of the entire source zone, which manifest itself in a certain regularity of the aftershock mechanisms discovered in the study of the 1970 Dagestan earthquake by Kuznetsova et al. (1976). In this paper, perhaps for the first time, compensatory movements are detected in a high-magnitude earthquake swarm without a pronounced main shock, which occurred in 2023 in Herat Province, Afghanistan. The results are supported by a series of seismological and satellite interferometric data.

The dynamic exploration and development of the Arctic zone of the Russian Federation is inextricably connected with the need to minimize technospheric risks, including those associated with the space weather effects on power equipment systems operated within the boundaries of the auroral oval. At the same time, accompanying monitoring of space weather parameters and geomagnetic field variations in the Arctic is carried out only through a group of satellites and several dozen magnetic stations located mainly in the United States, Canada, northern and central Europe. Obviously, the current situation practically excludes the possibility of promptly diagnostics of the level of geoinduced currents (GIC) for most of the Arctic zone of the Russian Federation, where in fact the only available indicator of the state of space weather is auroras. In the paper the authors propose an approach to interpreting the manifestation of auroras to assess the effects of space weather on objects and systems of high-latitude infrastructure. Thus, using the example of the “Vykhodnoy” substation of the “Severny Transit” main electrical network, it is shown that when recording auroras in the north, zenith and south, the most probable (averaged over 30 min) GIC level is 0.08, 0.23 and 0.68 A accordingly. In this case, the probability that the average half-hour GIC level will exceed 2 A (in the case of auroras in the north, zenith and south) is ∼6, ∼10 and ∼15%, respectively. In conclusion, ways of modernization and the limits of applicability of the proposed approach are considered.

The collection of paleomagnetic samples of the Lower Devonian Frænkelryggen Formation from the northwest of the island of West Spitsbergen is studied. The main carrier of the natural remanent magnetization of the studied rocks is hematite. Based on the component analysis, 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 on the Lower Devonian.

The results of rock magnetic studies and determination of relative paleointensity from sediments of Lake Shira, Khakassia, are presented. The NRM carrier minerals were determined from the hysteresis parameters, thermomagnetic and X-ray diffraction (XRD) analyses. The age of the sediments was determined by radiocarbon dating. According to these measurements, the column spans about 9100 years. The qualitative determinations of relative paleointensity were obtained from linear segments of the pseudo-Arai–Nagata diagrams. The quality of the determinations was evaluated by the following criteria: number of points used to calculate the slope; quality criterion (q), fraction of NRM destroyed in the paleointensity determination interval, and relative paleointensity determination error (σ). According to rock magnetic studies and XRD analysis, the magnetization carriers are represented mainly by single-domain and pseudo-single-domain magnetite and hematite. The comparison of the obtained series of relative paleointensity data with both the model paleointensity values calculated for Shira coordinates from 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]) and with absolute paleointensity, as well as the aggregate results of the studies on sedimentary and igneous rocks and on archaeomagnetic objects has shown that these data are in good agreement with each other and have common trends. This provides a rationale for using this methodology to determine paleointensity from sediments of modern lakes using the pseudo-Thellier method.

The hydrogeology of fault zones, especially at considerable depth, is perhaps the most poorly developed area of earthquake source mechanics. This is due both to the insufficient 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 these conditions, a fluid obviously has a very strong effect of on both the friction characteristics and the stress state in the vicinity of the slip zone. 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 start and stop of seismogenic ruptures. Constructing a complex computational model that adequately describes the processes of preparation, initiation, and stopping of various slip modes along faults, which is a recent trend in world seismology, requires developing the ideas about fluid dynamics of seismogenic faults.

This review summarizes recent information on the hydrogeology of fault zones. Models and ideas about the role of fluids at different stages of the seismic cycle, derived from the field data, laboratory and in situ experiments, and numerical calculations, are analyzed.