No 6 (2019)

ARTICLES
Geomagnetic variations during strong earthquakes
Spivak A.A., Riabova S.A.

Abstract

We analyze the geomagnetic effect caused by the strong earthquakes using the data from the Geophysical Observatory «Mikhnevo» (MHV) of the Institute of Geosphere of the Russian Academy of Sciences (IDG RAS) and from a number of observatories of the international INTERMAGNET network. It is shown that seismic events are accompanied by characteristic variations in the Earth’s magnetic field. These induced geomagnetic variations contain a clearly pronounced short-period component with a period of ∼0.5–0.8 min which is recorded during shallow earthquakes and a long-period component (∼5–20 min) observed in the most cases. The maximum amplitudes of the induced geomagnetic variations are ∼1.5–5 and ∼2–20 nT for the short-period and long-period components, respectively. It is noted that the induced geomagnetic perturbations recorded by the observatories at significantly different distances from the source of the earthquake feature almost simultaneous and morphologically similar behavior.

Физика Земли. 2019;(6):3-12
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On transformation of energy of geomagnetic disturbances
Gorokhov V.V., Karelin V.I., Selemir V.D.

Abstract

A mechanism responsible for the transformation of energy of geomagnetic disturbances into the energy of chemically active products is proposed. According to this mechanism, this transformation is implemented by electrolysis at the interfaces between the media with a different type of conduction under the passing of telluric currents induced by the variations of the geomagnetic field. The efficiency of the transformation of disturbance energy into the energy of electrolysis products is estimated. The energy flux absorbed by the Earth under geomagnetic disturbances is estimated. It is shown that the energy transferred to the chemical energy of the products of electrolysis is comparable with seismic energy. It is suggested that chemically active gaseous products of electrolysis affect seismic activity. It is also hypothesized that the electrolysis under the action of telluric currents induced by the variations of the geomagnetic field is one of the sources of outgassing of the Earth.

Физика Земли. 2019;(6):13-23
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On a possibility of geomagnetic reversal recording in dolerite sills of Norilsk region: results of mathematical modeling
Metelkin D.V., Lavrenchuk A.V., Mikhaltsov N.E.

Abstract

The possibility of reconstructing the geological chronicle by identifying the peculiarities in the variations of the Earth’s magnetic field associated with the reversals is one of the fundamental applications of paleomagnetism. The most detailed records of reversal events whose duration is, on average, one to ten thousand years have been recognized from the results of studying flood basalts of the large igneous provinces. At the same time, recent publications report the facts that are interpreted as a record of a geomagnetic reversal in the intrusion bodies. Inter alia, these data have been obtained for the relatively thin Ergalakh dolerite sills in the Norilsk region of the Siberian trap province which are supposed to have recorded the «Ivakinsky-Syverminsky» reversal corresponding to the Permian–Triassic boundary. The interpretation is based on the hypothesis of slow cooling of the intrusion during which its apical parts are magnetized during the Ivakinsky epoch of reversed polarity whereas the central parts acquire magnetization after the reversal during the Syverminsky time corresponding to normal polarity. In this paper, we consider the results of mathematical modeling to discuss the validity of these assumptions and the potential eligibility of subvolcanic intrusions as a source of information for studying geomagnetic reversals. It is shown that the duration of their cooling including the interval of the most probable magnetization is a few orders of magnitude shorter than the duration of the reversal transitions, whereas the presence of the components with normal and reversed polarity is most likely to be due to the effect of self-reversal.

Физика Земли. 2019;(6):24-33
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Paleomagnetic, sedimentological, and isotopic data on neoproterozoic periglacial sediments of Siberia: a new perspective on the problem of low-latitude glaciations
Shatsillo A.V., Rud’ko S.V., Latysheva I.V., Rud’ko D.V., Fedyukin I.V., Malyshev S.V.

Abstract

Paleo- and rock magnetic, sedimentological, and isotope geochemical study is carried out for the carbonate member of Late Neoproterozoic Nichatka Formation (Siberian Platform, western slope of the Aldan Shield) enclosed within glacial deposits corresponding to the hypothetical «Snowball Earth» event of global glaciation. Based on the sedimentological, rock magnetic, and geochemical indications it is established that sediments composing this member have varve-type seasonal stratification and, according to our estimates, have been accumulated for at most 13 thousand years. Obtaining the detailed paleomagnetic data for the Precambrian varves allowed us to reveal a linear trend in the distribution of the virtual geomagnetic poles and to associate it with the peculiarity of secular variation of the geomagnetic field during the time span of the Nichatka Formation.The paleomagnetic record in the periglacial sediments of the Nichatka Formation testifies to their deposition close to the equator which might be considered as supporting the Snowball Earth hypothesis. However, the absence of annual temperature fluctuations within the equatorial belt makes the formation of seasonal deposits at low latitudes barely possible and completely excludes such a possibility in the conditions close to total glaciation. The contradiction between paleoclimatic and paleomagnetic data is not explained in the context of the actualistic model of the geomagnetic field. The peculiarities of the paleomagnetic record in the Nichatka Formation, similar to the record of the field during the reversal, suggest that the geomagnetic field in the Neoproterozoic could be determined by substantial contribution of the low-latitude non-axial-dipole component. This peculiarity of the Neoproterozoic geomagnetic field can explain the entire set of the worldwide paleomagnetic data implying low latitude glaciations in the Neoproterozoic.

Физика Земли. 2019;(6):34-58
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Predictability of the rate of seismic energy in North America
Malyshev A.I.

Abstract

The predictability of the rate of seismicity and strong earthquakes of North America is assessed based on the catalog of the U.S. Geological Survey for 1900–2016. A second-order nonlinear differential equation is used as the mathematical model of the study; the algorithms for optimization and predictability assessment are developed by the author. The conducted estimates show high predictability of the rate of seismic energy. Among 1422 analyzed strong earthquakes, the foreshock predictability is revealed for 120 earthquakes (215 thousand determinations) and the aftershock predictability for 1410 earthquakes (more than 3 million determinations). The predictability related to the strong earthquakes appears at small (1.5–3 km) radius of the samples of hypocenters and increases in terms of the number of the predicted earthquakes with the increase in the radius of the samples. The forecast distances in time are, on average, tens of days for foreshock predictability and thousands of days for aftershock predictability. The obtained results demonstrate a very promising potential of the approximation-extrapolation approach for forecasting both the strong earthquakes themselves and the subsequent aftershock decay of seismic activity.

Физика Земли. 2019;(6):59-75
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Microcracks in basalt and tonalite at friction
Vettegren V.I., Ponomarev A.V., Mamalimov R.I., Shcherbakov I.P., Arora K., Srinagesh D., Chadha R.

Abstract

The growth rate and size of microcracks formed in the surface layer of basalt and tonalite (granodiorite) at friction are studied using luminescence. It is found that upon breaking of crystal lattices of labradorite and quartz contained in these rocks, triboluminescence signals arise. Each signal corresponds to an embryo microcrack whose surface contains electronically excited free radicals ≡Si-O-, Fe3+ ions, and electron traps. The average growth rate of embryo microcracks in basalt varies from ≈0.6 to ≈1 km/s and in tonalite, from ≈0.7 to ≈1.3 km/s. The sizes of embryo microcracks in basalt range within ≈3 to 5.5 μm and in tonalite from ≈3.5 to ≈ 6.5 μm.

Физика Земли. 2019;(6):76-83
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Microseismic sounding and active faults of the Kerch-Taman region
Ovsyuchenko A.N., Gorbatikov A.V., Rogozhin E.A., Andreeva N.V., Stepanova M.Y., Lar`kov A.S., Sysolin A.I.

Abstract

The results of integrated geological and geophysical studies of active faults and deep structure of the Kerch-Taman region are presented. Data on the deep structure of potential sources of strong earthquakes determining the level of seismic hazard are obtained. Examples of the active faults, well studied on the surface, show that these structures are clearly spotted by microseismic sounding method as the displacements of contrasting layers in the section at a depth of a few km or as narrow low-velocity bodies. In the zones of the Tobechik, South Azov, and Phanagoria faults at depths of 7–12 km, high-velocity isometric inclusions are established. These segments are especially important for making ther repeated MSM measurements for seismic forecasting purposes.

Физика Земли. 2019;(6):84-95
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Relationship between the parameters of infrasound waves and the energy of the source
Adushkin V.V., Rybnov Y.S., Spivak A.A., Kharlamov V.A.

Abstract

A new phenomenological model describing the propagation of acoustic disturbances in the stratospheric waveguide is proposed based on instrumental observations of infrasound signals from high-power explosive sources in the atmosphere. A generalized relationship between the energy of the acoustic source in the atmosphere and the characteristic frequency in the spectrum of the acoustic signal is obtained. The developed model is verified against the description of natural and manmade acoustic sources with the known energy. It is shown that the proposed model agrees with the observations and the data obtained in the other works.

Физика Земли. 2019;(6):96-106
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Parameterization of a priori geological knowledge in seismic inversion
Epov K.A.

Abstract

An approach to parameterization of prior geological knowledge concerning the changes in depositional environment in space and geological time for their quantitative use in the workflow of seismic inversion is presented. The idea is to describe the observed or expected facies diversity in terms of a few statistically independent factors (generalized geological variables). The topology and metrics of the model are determined by the set of basic depositional environments and the statistics of facies transitions. The introduced parameters make it possible to estimate the occurrence probability of different facies at each model point. The proposed technique can be applied for regions with various degree of detail of the existing geological knowledge and amount of available well logging data.

Физика Земли. 2019;(6):107-129
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On the problem of elastic anisotropy estimation in the rocks with quasi orthotropic symmetry
Gorbatsevich F.F.

Abstract

The principles for estimating the degree of elastic anisotropy of the medium (the rocks) with transverse isotropic and orthorhombic symmetry are considered. Because of the structural heterogeneity, rocks cannot be considered as strictly having a single type of symmetry. With this fact taken into account, formulas are developed for estimating the elastic anisotropy of the rocks with quasi-orthotropic symmetry from the velocities of compressional and shear waves. The criteria for separating the media into weakly and strongly anisotropic are proposed. The developed parameters can be used for mass determinations of elastic anisotropy of rocks.

Физика Земли. 2019;(6):130-139
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On the tilts caused by equilibrium fluctuations of atmospheric pressure: effect of topography
Tsurkis I.Y.

Abstract

The influence of the relief on baric tilts is studied. Main attention is focused on two-dimensional problem. It is assumed that variations of baric field are equilibrium (horizontal component of pressure gradient is absent) and the relief is finite. The latter means that the area between the topographic profile and the abscissa axis is finite. It is shown that this area is the only geometric parameter that determines vertical displacements and tilts in the far zone. The asymptotics for the variations in vertical displacements and tilts are written out. The generalization to the three-dimensional case is presented.

Физика Земли. 2019;(6):140-150
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