Izvestiya, Physics of the Solid Earth最新文献

The central Indian Ocean displays one of the most perplexing intra-plate deformations in an oceanic realm. Despite several studies attempting to explore this intriguing phenomenon, understanding about its structural style and spatiotemporal genesis is still debated. Earlier geophysical and deep-sea drilling studies proposed the late Miocene onset of extensive crustal deformation. Subsequent geophysical studies, however, speculated that parts of the deformation may have begun significantly earlier (c.a. 15.4–13.9 Ma) consequent upon contemporaneous dynamics of the India-Eurasia convergence. Alternative hypotheses argue about the crucial role played by temporal variations in the rotational motion of the India-Somalia-Capricorn plates. Here we examine new deep penetrating multi-channel seismic reflection data from the central Indian Ocean region to gather the style and extent of structural deformation in this region. We explore plausible mechanisms and estimate the onset of extensive intra-plate deformation. Based on seismic-stratigraphic interpretation and cumulative fault-throw analyses of new regional seismic profiles, our study confirms that extensive faulting occurred during the early Miocene period across the CIDZ. We document that an average of 40% of faults were activated around or before early Miocene time, showing maximum throw at a regional unconformity dating to 17–18 Ma. We also identify distinct categories of deformation manifested in these faults. While our findings endorse significantly prior to the late Miocene time of onset of deformation, new subsurface images offer much-improved constraints on prominent stratigraphic and structural variations.

This work is a continuation of the authors’ research on solving inverse problems of mathematical geophysics in a linear formulation. Unlike previous works, where the solution was built on the basis of volumetric integral equations, boundary integral representations and emerging boundary integral equations are used here to solve the inverse coefficient problem of geoelectrics to find the constant electrical conductivity of a local isotropic inclusion, located in a piecewise-constant electrical conductivity isotropic enclosing medium.

This work is aimed at estimating the long-term continuing measurements of the acceleration of gravity at the Ledovo fundamental gravity station and first order stations of the gravimetric network of the Russian Federation. The observations are carried out by absolute gravimeters beginning from the mid-1970s to the present time. It is shown that the observed value of the acceleration of gravity at the Ledovo station has a tendency to decrease during last 45 years; according to our estimates, the value decreased by 32 µGal. The measurements carried out at first order gravity stations in Russia after renewal of network maintenance are compared with measurements carried out in the 1980s.

In this paper, we determine the location of the hypocenter and the magnitude of the earthquake of September 11/23, 1888 based on macroseismic data published in the Russian periodic in Russian, Armenian, and Georgian languages. Calculations showed that the magnitude of the earthquake was previously significantly underestimated, due to which it was not included in the catalog of strong earthquakes in the Caucasus test region (Shebalin and Tatevossian, 1997). The accuracy of the location of the hypocenter makes it possible to identify the active fault, with which the source of the 1888 earthquake is associated. The earthquake with M_w = 6.6 that occurred almost 100 years later confirms the long-term activity of the Western branch of the East Anatolian fault zone.

This study is devoted to application of some new statistical methods to analysis of the spatial structure of the seismic field in a seismically active region in the neighborhood of Japan bounded by the following coordinates: 28°–50° north latitude, 130°–150° east longitude. The estimates of the seismic flux were obtained by using the k-nearest neighbors method for the magnitude interval m ≥ 5.2. The highest values of seismic flux intensity of about 10^–4 (frac{1}{{{text{year}}{kern 1pt} - {kern 1pt} {text{k}}{{{text{m}}}^{{text{2}}}}}}) are located at depths of down to 100 km and manifest themselves in the neighborhood of the Tohoku megathrust earthquake. The spatial resolution of the intensity estimates is ranging from 33–50 km in the regions with a high intensity to 100 km and larger in the zones with a weak intensity. It has been shown that the seismic filed parameters—intensity λ, slope of the magnitude–frequency graph β, maximum possible magnitude m₁—have different scales of their spatial variability and, thus, it is necessary to apply different scales of spatial averaging to them. Based on the Gutenberg—Richter truncated distribution model, the estimates are obtained for the slope of the magnitude–frequency graph (b‑value) and the upper boundary of the distribution m₁. An original method is proposed for determining the optimal averaging radius for an arbitrary cell of the space grid. The method is based on the use of the statistical coefficient of variation of the corresponding parameter. For the considered region, the estimate of the maximum possible magnitude М_max = 9.60 ( pm ) 0.41 was obtained with consideration of the correction for bias.

In this paper, we kinematically analyze the movements of plates and blocks of the region of southeastern Turkey, where strong earthquakes occurred on February 6, 2023, based on a homogeneous database of displacement velocities of GNSS permanent monitoring stations. Along the East Anatolian fault zone from 2008 to 2018, the Arabian Plate was established to shift relative to the Anatolian Plate, which corresponds to a left shift (without a normal component) at a rate from 1 cm/yr in the eastern part to 0.8 cm/yr in the western part. Along the Chardak fault, displacements corresponding to the left shift occurred at a rate of less than 0.7 cm/year. The revealed kinematics is confirmed by focal mechanisms and cosesismic displacements of the studied earthquakes. The M7.5 earthquake that occurred directly on the Chardak fault is not an aftershock of the M7.8 earthquake, but is a relatively independent event. An analysis of the seismic regime shows that the stresses on the East Anatolian fault after the main M7.8 event are relieved by the first large latitudinal fault zone (the Chardak fault). The results of our study suggest that the counterclockwise rotation of the Anatolian and Arabian plates associated with the opening of the Red Sea Rift is most likely decisive for the general kinematics of the plates in the region.

This paper is devoted to the 80th anniversary of the discovery of Alfven waves, which play an important role in physics, radiophysics, astrophysics, and Earth physics. The emphasis is on the ponderomotive redistribution of plasma in the Earth’s magnetosphere under the action of Alfven and ion-cyclotron waves. At relatively small distances from the Earth, the ponderomotive force is buoyant, i.e., is directed upwards, regardless of whether an Alfven wave propagates towards the Earth or away from it. In the near-equatorial zone of the central regions of magnetosphere, waves in the Pc 1 range push the plasma to the minimum of geomagnetic field, so that a maximum of plasma density arises on the equator at sufficiently high wave intensity. A bifurcation occurs at the magnetosphere’s periphery, and the maximum is split into two maxima, the distance between which increases while moving away from the Earth. The polar wind, acceleration of heavy ions, and fictitious nonlinearity of the surface impedance of the Earth’s crust are also briefly discussed.