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编号 3 (2024)
Articles
Seismic Pulses before the February 27, 2010, M = 8.8 Chile Earthquake
摘要
The study analyzes the records of vertical velocity of the Earth’s surface motions near broadband seismic stations located on the west coast of South America and in the adjacent region of the Pacific Ocean where the Mw 8.8 earthquake occurred on February 27, 2010. Starting from 2009, asymmetric seismic pulses lasting several hundred seconds have been detected in the records of some stations. These pulses appeared under quiet weather conditions and geomagnetic activity. It is believed that the earthquake was preceded by tectonic movements in the oceanic and continental lithosphere.
3-9
Prediction Results for the Strongest Earthquakes in Southern Turkey on February 6, 2023
摘要
On February 6, 2023, two devastating earthquakes struck southern central Turkey, nin hours apart. The ground shaking from these earthquakes even swept over a significant part of northwestern Syria. In this paper, we consider the locations of the epicenters of these earthquake relative to the prediction of М ≥ 6.5 earthquake epicenters in Anatolia and adjacent regions, which was made in 1973 by I.M. Gelfand, V.I. Keilis-Borok and their colleagues using the Kora-3 pattern recognition algorithm based on morphostructural zoning data. We also present the results of early detection of periods with an increased probability of the strongest earthquakes as determined by the medium-term prediction algorithm for M8 earthquakes. It is found that the epicenters of the February 6, 2023 earthquakes occurred in a knot identified in 1973 as potentially earthquake-prone for М ≥ 6.5, and both events occurred within the spatial and temporal boundaries of the alert area diagnosed by the M8 algorithm in July 2021.
10-17
The Effect of Heavy Inclusions in the Upper Crust on Thermoconvective Instability of the Lithosphere
摘要
The method of linear theory for small perturbations is used to study the stability of heavy inclusions in the upper crust. The existence of such inclusions of increased density is associated with chemical heterogeneity or phase transitions. At small deformations considered in the linear stability theory, the material undergoes transient creep which is described by the Andrade rheological model. Under this rheology, the convective instability of thickened segments of the lithosphere is oscillatory: the increment is a complex number whose real part is close to zero (threshold instability). Heavy inclusions in the upper crust introduce a small complex correction to the increment that determines the convective instability of the lithosphere, slightly increasing the real and imaginary parts of the increment, enhancing the instability and increasing the oscillation frequency.
18-29
Lake Baikal Microseisms Based on Regional Seismic Network Data
摘要
Seismic ambient noise in the regional seismic network in the central part of the Baikal rift is studied. The probabilistic approach is used to thoroughly investigate the pattern of diurnal variations in microseisms and to analyze amplitude level and frequency content of spatial anomalies and 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 the northern part of the lake. The direction of the back azimuth in the frequency range of about 1 Hz indicates the location of the lake, suggesting that these signals can be identified as lake microseisms. The high coherence values suggest a linear relationship between the wind speed and the occurrence of lake microseisms. The detailed analysis of the spectral and polarization parameters of seismic ambient noise revealed two types of lake microseisms with frequencies of 0.4–0.7 and 0.7–1.5 Hz. The first frequency interval is likely to correspond to single-frequency lake microseisms, while the second interval contains the frequency ranges of dual-frequency microseisms.
30-50
Magnetostratigraphy of the Permian–Triassic Boundary in the Lower Reaches of the Vetluga River, East European Platform, Nizhny Novgorod Region
摘要
We present the results of detailed paleomagnetic studies of six Permian-Triassic boundary sections in the central part of the East European Platform, 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, allow for the development and substantiation of magnetostratigraphic scales for each section, as well as for their correlation and the construction of a 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.
51-74
Late Paleozoic Remagnetization on the Western Slope of the Southern Urals: Age and Geotectonic Implications
摘要
The paper presents 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 different parts of the Bashkirian megazone (in the northern, central and southern part of the structure) were sampled. The studied intrusions have Riphean age, however, like 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. This article will discuss the secondary Late Paleozoic component of natural remanence magnetization.
According to the paleomagnetic data obtained, the secondary Late Paleozoic component in most of the Bashkirian megazone is post-fold, 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 did not 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°, N = 6 from 6 areas (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 million years. 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.
75-106
What Does the Archaeomagnetic Record of Fired Ceramics Reflect?
摘要
A complex of archaeomagnetic and rock-magnetic studies is conducted to compare the archaeomagnetic intensity determined by the Thellier–Coe and Wilson methods with the known “true” value of the geomagnetic field during the firing of the ceramic samples manufactured on February 21, 2017 in Myshkin, Yaroslavl region, Russia.
The obtained results show two different values of archaeomagnetic intensity corresponding to two temperature intervals. The values obtained in the low-temperature interval (∼150–350°C) are approximately 13 µT lower than the true value, while the values obtained in the interval of ∼350–600°C are fairly close to the “true” ones. The cause of the phenomenon is likely due to the presence of small magnetic grains in the ceramic under study, which are close in size to superparamagnetic ones and are capable of resuming their growth upon heating and reaching the particle sizes in a single-domain state.
The results of rock-magnetic studies suggest that thermoremanent magnetization in the studied ceramics is carried by grains of oxidized magnetite, hematite, and possibly ε-Fe2O3.
107-128
On Constructing Magnetic and Gravity Images of Mercury from Satellite Data
摘要
A new technique for simultaneous reconstruction of “gravity” and “magnetic” images of Mercury from satellite data based on the regional version of S-approximations is proposed. The mathematical statement of the inverse problem on finding the images of a planet from the data on the potential fields recorded at different times with different accuracy is reduced to solving ill-conditioned systems of linear algebraic equations (LAES) with approximate right-hand sides. Based on the analytical approximations of the Mercury’s magnetic and gravity fields determined from the solution of the ill-conditioned SLAE, the distributions of the equivalen sources on the spheres are determined. The results of the mathematical experiment on constructing the magnetic image of Mercury from the radial component of the magnetic induction vector analytically continued towards the field sources are presented.
129-148