Izvestiya, Physics of the Solid Earth最新文献

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.

Abstract—The capabilities of a combination of passive seismic methods to study the geological structure of the upper part of the Earth’s crust compared to active methods are analyzed using case examples. The passive methods include microseismic sounding, Nakamura’s horizontal-to-vertical spectral ratio method (HVSR), seismic interferometry, and, for anthropogenic sites, ambient vibration testing using industrial signals. Three examples are considered: a zone of a platform tectonic earthquake, a kimberlite pipe, and a hydroelectric dam with foundation site. The results of the passive and active seismic methods agree well. Passive methods give more diffuse horizontal boundaries but clearly identify near-vertical heterogeneities. Combining passive methods is effective for reconnaissance studies and in the remote regions that are difficult to access by active observation techniques. Combination of passive methods enables simultaneous processing of seismic records obtained through different passive methods, with a minimum of two sensors required.

Abstract—The concept of Alfvén waves plays a key role in the theory of ultralow-frequency (ULF) electromagnetic oscillations of extraterrestrial origin. This article is dedicated to the 80th anniversary of the discovery of Alfvén waves. It focuses on the ionospheric Alfvén resonator (IAR). IAR excites ultralow-frequency oscillations in the Pc1 range (0.2–5 Hz). When computing the oscillation spectrum within the standard model, it is assumed that the IAR is an autonomous dynamical system. In contrast, in this paper, IAR is treated as a specific subsystem of the general system of Alfvén oscillations of geomagnetic field lines. In other words, we proceed from the idea that IAR, in general, is not an autonomous oscillatory system. The problem about IAR spectrum is discussed in the context of the general problem on the spectrum of magnetohydrodynamic oscillations of the Earth’s magnetosphere. The corresponding Sturm–Liouville problem is formulated. Analytical solutions of the problem are considered in the Wentzel–Kramers–Brillouin approximation. It is pointed out that the problem of IAR spectrum has to be solved by numerical methods due to the rather complicated distribution of the Alfvén velocity along the geomagnetic field lines.

Abstract—The key parameters of an earthquake are magnitude, epicenter coordinates, and depth. Depth has often a crucial influence on the macroseismic effect from certain earthquakes. This makes the statistics of earthquake occurrences at certain depths important information, e.g., for the assessment of seismic risk. 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 be the most accurate to describe the depth distribution of these crustal earthquakes. The Weibull distribution is also preferred when considering the western (Altai‒Sayan) and eastern (Baikal Rift Zone) parts of the region separately. The maximum of the distribution is found to be at 9 km depth for the Baikal rift zone and at 7 km for the Altai‒Sayan zone.

Abstract—We present the results of detailed paleomagnetic studies of six Permian–Triassic boundary sections in the central part of the East European Platform, which are located in the lower reaches of the Vetluga River: Astashikha, Voskresenskoe, Znamenskoe, Prudovka, Sosnovka, and Sukhoborka. The paleomagnetic data, which meet the modern quality standards for laboratory processing, together with the results of biostratigraphic studies, make it possible to develop and substantiate the magnetostratigraphic scales for each section, as well as to correlate them and to compile a composite magnetic polarity scale for the Permian–Triassic sedimentary complex of the Vetluga River. Rock-magnetic characteristics are determined for each of the studied sections, and paleomagnetic poles of the East European Platform are calculated for the Late Permian and Permian–Triassic boundary.

Abstract—Possible causes of surface subsidence of the pyroclastic flow formed on the slopes of the Shiveluch volcano, Kamchatka, during the eruption on August 29, 2019 are studied. A series of InSAR (Interferometric Synthetic Aperture Radar) images from acquisitions by the European Space Agency Sentinel-1A satellite for a period from May to October in 2020 and 2021 are used to construct maps of the displacement rates of the volcano surface. An area with large subsidence coinciding with the area of pyroclastic flow is revealed on the volcano’s southeastern slope. The maximum subsidence rates are found to be 385 mm/year in 2020 and 257 mm/year in 2021. The thickness of the pyroclastic deposits is estimated from radar images for 2020. The dependence of the subsidence rate on flow thickness has a significant scatter with a rather high correlation coefficient (‒0.69). A thermomechanical model has been constructed, which takes into account compaction of the deposited material due to changes in porosity and density over time. According to the model, to explain the dependence of the subsidence rate of the flow surface on the thickness of rocks, it is sufficient to assume that in addition to surface subsidence, flow cooling was accompanied by a small change in porosity occurred, which, depending on the initial flow temperature, made up to 1.5 to 1.7% for the period from 2019 to 2021. The scatter in the relationship “subsidence rate versus flow thickness” is explained for by the erosion of pyroclastic deposits.

Abstract—Peculiarities of microseismic ambient noise are studied based on the data from the stations of regional seismic network located in the central part of the Baikal rift. The probabilistic approach is used to thoroughly investigate the pattern of diurnal variations in microseisms and to analyze the amplitude level and frequency content of the spatial anomalies and the temporal changes (seasonal and annual). Based on the 2020–2021 data, a regional probabilistic model of the microseismic noise is built in a wide range of periods. The study of microseisms in the frequency band of about 1 Hz revealed a seasonal anomaly against the level of the global minimum in the microseismic noise power spectrum. The anomaly is observed from May to December at seismic stations surrounding Lake Baikal except for its northern part. The back azimuth direction in the frequency range of about 1 Hz indicates the arrivals from the location of the lake, suggesting that these signals can be identified as lake-generated microseisms. The high values of the coherence function testify to a linear relation between the wind velocity and the occurrence of lake microseisms. The detailed analysis of the spectral and polarization parameters of the seismic ambient noise revealed two types of lake-generated microseisms with frequencies of 0.4–0.7 and 0.7–1.5 Hz. The first frequency interval is likely to correspond to the single-frequency lake-generated microseisms, while the second interval covers the frequency ranges of the dual-frequency microseisms.

Abstract—In the paper, we present the results of paleomagnetic studies on numerous intrusive bodies of the Bashkirian megazone, a major tectonic zone of the Southern Urals. More than 70 intrusions in various parts of the Bashkirian megazone (in the northern, central, and southern part of the structure) were sampled. The studied intrusions have Riphean age. However, as a significant part of the rocks of the Southern Urals, these intrusive bodies were remagnetized during the Late Paleozoic collision within the Urals fold belt. Here, we discuss the secondary Late Paleozoic component of natural remanent magnetization. According to the obtained paleomagnetic data, the secondary Late Paleozoic component in most of the Bashkirian megazone is post-folding, i.e., formed after the completion of the main phase of fold deformations in the Southern Urals. A comparison of paleomagnetic directions obtained from intrusions in different parts of the Bashkirian megazone showed that there were no significant movements of individual parts of the Bashkirian megazone relative to each other after the formation of the Late Paleozoic component. The Late Paleozoic remanence component yielded a paleomagnetic pole of Plong = 171.6°, Plat = 39.9°, α₉₅ = 5.9°, and N = 6 from six regions (38 sites) in the Bashkirian megazone. The obtained pole is statistically indistinguishable from the mean of 15 poles for Stable Europe with ages of 280–301 Ma. Thus, the secondary Late Paleozoic component in the Bashkirian megazone formed approximately 280–301 million years ago, after which the Bashkirian megazone did not experience any relative motions with respect to the East European craton.