Vol 54, No 1 (2018)

The results of an instrumental and analytical investigation of the products of mineral and textural transformations in the tectonic slickensides and fault gouge in the near-surface terrigenous sedimentary rocks (clays, arkose sandstones, shungites) which have undergone localized deformations in fault zones of presumably seismogenic origin are presented. Based on this, several peculiarities in the behavior of a dynamic slip in the upper transition horizon from aseismic to seismogenic mode of faulting in the Earth’s crust are elucidated. The changes in the mineral phase compositions of the fault facies against the protolith composition are estimated; the parameters of the temperature regime and thermal energy balance of deformational metamorphic reactions are determined. The probable causes of instability in the faults, the mechanisms of the loss of strength, the weakening and strengthening during seismogenic dynamic slip are considered. The role of tribochemical phenomena in the course of a rock’s transformation into a fault gouge and the related energy effects are discussed. An inventory of the possible energy costs on the processes of transforming material in dynamic slip zones is compiled.

The average relationship is established between the basic magnitude for the Kamchatka regional catalog, M_L, and modern moment magnitude M_w. The latter is firmly tied to the value of the source seismic moment M₀ which has a direct physical meaning. M_L magnitude is not self-reliant but is obtained through the conversion of the traditional Fedotov’s S-wave energy class, K_S1,2^F68. Installation of the digital seismographic network in Kamchatka in 2006–2010 permitted mass estimates of M₀ and M_w to be obtained from the regional data. In this paper we outline a number of techniques to estimate M₀ for the Kamchatka earthquakes using the waveforms of regional stations, and then compare the obtained M_w estimates with each other and with M_L, based on several hundred earthquakes that took place in 2010–2014. On the average, for M_w = 3.0–6.0, M_w = M_L–0.40; this relationship allows obtaining M_w estimates (proxy-M_w) for a large part of the regional earthquake catalog with M_L = 3.4–6.4 (M_w = 3.0–6.0).

There are numerous models of geomagnetically induced currents in which the role of the main sources is allotted to the variations in the intensity of the auroral electrojet inducing the currents flowing along the latitude. Based on this it is believed that magnetic disturbances mainly threaten technological systems that are elongated in the longitudinal (W–E) direction. In this work, we make an attempt to employ new characteristics to describe the variability of the geomagnetic field during the geomagnetic storm of March 17, 2013. These characteristics, calculated from the data of the IMAGE magnetometer network stations, are compared to the records of the induced currents in the power lines on the Kola Peninsula and in Karelia. The vector technique revealed a considerably lower variability of the horizontal component of the geomagnetic field compared to its derivative. Quantitative estimates of the variability supported the fact that the variations of the field occur on a commensurate scale both in magnitude and direction. These results cannot be accounted for by the simple model of the extended ionospheric current and demonstrate the importance of allowing for small-scale current structures (with the spatial scales of a few hundred km) in the calculations of the geomagnetically induced currents. Our analysis shows that the geomagnetically induced currents are not only hazardous for the technological objects oriented in the longitudinal (W–E) direction but also for those elongated meridionally.

The burial history and thermal evolution of the lithosphere within the passive nonvolcanic Antarctic margin in the region of the Mawson Sea are numerically reconstructed for the margin areas along the seismic profile 5909 with the use of the GALO basin modeling system. The amplitudes of the lithosphere stretching at the different stages of continental rifting which took place from 160 to 90 Ma ago are calculated from the geophysical estimates of the thickness of the consolidated crust and the tectonic analysis of the variations in the thickness of the sedimentary cover and sea depths during the evolution of the basin. It is hypothesized that the formation of the recent sedimentary section sequence in the studied region of the Antarctic margin began ~140 Ma ago on a basement that was thinned by a factor of 1.6 to 4.5 during the first episode of margin stretching (160–140 Ma) under a fairly high heat flux. The reconstruction of the thermal regime of the lithosphere has shown that the mantle rocks could occur within the temperature interval of serpentinization and simultaneously within the time interval of lithospheric stretching (–160 < t <–90 Ma) only within separate segments of profile 5909 in the Mawson Sea. The calculations of the rock strength distribution with depth by the example of the section of pseudowell 4 have shown that a significant part of the crust and uppermost mantle fall here in the region of brittle deformations in the most recent period of lithosphere stretching (–104 to–90 Ma ago). The younger basin segments of profile 5909 in the region of pseudowells 5 and 6 are characterized by a high heat flux, and the formation of through-thickness brittle fractures in these zones is less probable. However, serpentinization could take place in these areas as in the other margin segments at the stage of presedimentation ultra slow basement stretching.

The native iron particles that were previously detected by thermomagnetic and microprobe analyses in the sediments of different age in many regions of the world are of extraterrestrial origin. The similarity in the compositions, grain shapes, and sizes observed in the extraterrestrial and terrestrial particles of native iron testifies to the common production conditions of iron particles during the formation of planets. In this paper, the single finding of terrestrial iron in the lacustrine sediments of the Zhombolok volcanic region, East Sayan, is discussed. The uniqueness of the results indicates that the spatial distribution of the particles of native iron is limited to a fairly narrow area around their source—volcanic eruption or/and the fall of a large meteorite.

Based on the theory of two-phase interacting nanoparticles, the formation of thermoremanent and chemical remanent magnetization in nanosized titanomagnetites is modeled. It is shown that the value of thermoremanent magnetization barely depends on the degree of titanomagnetite exsolution whereas, chemical remanent magnetization which emerges during the exsolution increases up to at most the value of thermoremanent magnetization. The values of the ratio of thermoremanent to ideal magnetization, R_t, fall within the limits 0.8 ≤ R_t ≤ 1. The analogous ratio of chemical remanent magnetization to the ideal R_c are below R_t at all stages of the exsolution. Besides, the magnetic interaction between the nanoparticles reduces the values of thermoremanent and chemical magnetization but barely affects the ratio.

The results of detailed paleomagnetic studies in seven Upper Permian and Lower Triassic reference sections of East Europe (Middle Volga and Orenburg region) and Central Germany are presented. For each section, the coefficient of inclination shallowing f (King, 1955) is estimated by the Elongation–Inclination (E–I) method (Tauxe and Kent, 2004) and is found to vary from 0.4 to 0.9. The paleomagnetic directions, corrected for the inclination shallowing, are used to calculate the new Late Permian–Early Triassic paleomagnetic pole for the East European Platform (N = 7, PLat = 52.1°, PLong = 155.8°, A95 = 6.6°). Based on this pole, the geocentric axial dipole hypothesis close to the Paleozoic/Mesozoic boundary is tested by the single plate method. The absence of the statistically significant distinction between the obtained pole and the average Permian–Triassic (P–Tr) paleomagnetic pole of the Siberian Platform and the coeval pole of the North American Platform corrected for the opening of the Atlantic (Shatsillo et al., 2006) is interpreted by us as evidence that ~250 Ma the configuration of the magnetic field of the Earth was predominantly dipolar; i.e., the contribution of nondipole components was at most 10% of the main magnetic field. In our opinion, the hypothesis of the nondipolity of the geomagnetic field at the P–Tr boundary, which has been repeatedly discussed in recent decades (Van der Voo and Torsvik, 2001; Bazhenov and Shatsillo, 2010; Veselovskiy and Pavlov, 2006), resulted from disregarding the effect of inclination shallowing in the paleomagnetic determinations from sedimentary rocks of “stable” Europe (the East European platform and West European plate).

Based on the observation data for hundreds of the main shocks and thousands of aftershocks, the existence of effect of round-the-world surface seismic waves is demonstrated (let us conditionally refer to them as a round-the-world seismic echo) and the manifestations of this effect in the dynamics of the repeated shocks of strong earthquakes are analyzed. At the same time, we by no means believe this effect has been fully proven. We only present a version of our own understanding of the physical causes of the observed phenomenon and analyze the regularities in its manifestation. The effect is that the surface waves excited in the Earth by the main shock make a full revolution around the Earth and excite a strong aftershock in the epicentral zone of the main shock. In our opinion, the physical nature of this phenomenon consists in the fact that the superposition leads to a concentration of wave energy when the convergent surface waves reach the epicentral zone (cumulative effect). The effect of the first seismic echo is most manifest. Thus, the present work supports our hypothesis of the activation of rock failure under the cumulative impact of an round-the-world seismic echo on the source area which is releasing (“cooling”) after the main shock. The spatial regularities in the manifestations of this effect are established, and the independence of the probability of its occurrence on the main shock magnitude is revealed. The effect of a round-the-world seismic echo can be used to improve the reliability of the forecasts of strong aftershocks in determining the scenario for the seismic process developing in the epicentral zone of a strong earthquake that has taken place.