Izvestiya, Physics of the Solid Earth最新文献

The upper mantle and the transition zone of the Baikal rift zone (BRZ) are studied. The observations are analyzed from P-wave receiver functions. It is found that in the BRZ central and northeastern part, the P410s converted seismic phase is preceded by a precursory wave with negative polarity which is formed in the low S-wave velocity layer at a depth of 350–410 km. A similar precursory wave with low S-wave velocity and negative polarity is formed at a depth of 600–660 km. The low-velocity layers are interpreted as resulting from the hydration of wadsleyite and ringwoodite during the subduction of the Pacific lithosphere. A similar study of the mantle in Central Mongolia found no expected signs of hydration. The modeling of the lithosphere–asthenosphere system in Central Mongolia by joint inversion of the body wave receiver functions and surface wave dispersion curves reveals a very thin lithospheric lid beneath Khangai and a thick layered asthenosphere down to a depth of 200 km with a lithospheric inclusion between low-velocity layers.

Currently, bending deformations of lithospheric plates are calculated based on Kirchhoff’s theory of bending of thin plates, which was formulated about 170 years ago. This paper examines the possibility of refining these calculations based on the theory of bending of thick plates developed by Timoshenko and Reissner. A new unified derivation is presented of the Timoshenko equations for 2D bending of beams and the Reissner equations for bending of slabs by direct transformation of the general elasticity equations with a simple approximate replacement of power-cubic functions with effective linear ones. This allows a more detailed and clearer understanding of the differences between the equations and the sense of the simplifications made in these theories. By comparing the analytical solutions of the Timoshenko and Reissner equations with the known test analytical solutions of the exact elasticity equations, quantitative estimates of the accuracy of these theories are given.

Abstract—During the magnetotelluric studies in North Vietnam, simultaneous Phase Roll Out from Quadrant effect was detected in the behavior of impedance phases Z_xy and Z_yx at one of the sounding sites, CTH, in the Cam Thuy district, Thanh Hoa province. The investigation of this phenomenon has shown that it is accompanied by negative (directed upwards) components of the Umov–Poynting vector of electromagnetic energy flux in the entire range of the recorded periods of magnetotelluric variations. This energy flux direction remains unchanged when the initial coordinate system is rotated by angles of 45° and 60°. Another characteristic feature of this phenomenon is an unusual behavior of the apparent resistivity curves: the apparent resistivity magnitudes increase starting from a period of 200 s up to a period of 10⁴ s, and this increase occurs practically along the asymptote. The analysis of the magnetotelluric field polarization and phase tensor asymmetry parameter (skew angle) β has shown that the section is characterized by significant three-dimensional (3D) distortions which manifest themselves by β values ranging between 20° and 90°.

Abstract—The paper presents an attempt to estimate the contribution of thermal processes in the Earth’s crust to earthquake generation. As a case study, the seismically active junction zone of the Chu depression and Kyrgyz ridge of the Northern Tien Shan is considered. The analysis is based on the previously constructed models of temperature, petrophysical characteristics, and elastic moduli. The silica content model derived from seismic tomography data is used to build a lithotype model. The thermal conductivity model is constructed and used in conjunction with the temperature model to create a depth model of the heat flow density. The shear stress and thermoelastic stress models derived from density, elastic moduli, and temperature models are compared with the distribution of earthquake hypocenters in the region. The comparison suggests that on the scale of the seismically active junction zone of the Chu depression and the Kyrgyz ridge of the Northern Tien Shan, seismicity is mainly determined by thermomechanical effect induced by hot ascending flow of acid magma rising from the upper mantle beneath the Muyunkum–Narat median massif.

Abstract—It is shown that most marsquakes epicenters are located in the zones of extension and fairly high shear stresses associated with deviation of the planet from hydrostatic equilibrium. In this paper, non-hydrostatic stresses in the interior of Venus are calculated for two types of models: an elastic model and a model with a lithosphere of variable thickness (150–500 km) covering a weakened layer that has partially lost its elastic properties. Numerical modeling of the system of elastic equilibrium equations for a gravitating planet is carried out with a step of 1° × 1° degrees in latitude and longitude down to a depth of 480 km, which is the first phase transition in the mantle. The boundary conditions of the problem are the topography and the gravitational field of the planet. In general, the level of nonhydrostatic stress on Venus is not very high. On the surface and in the crust, the highest shear stresses are observed in the region of the Maxwell Montes on Ishtar Terra. Beneath the Maxwell Montes, shear stresses in the crust reach 80 MPa and compressive stresses, 125–150 MPa, depending on the model. Tensile stresses around this area are about 20 MPa. The highest tensile stresses occur in the regions beneath such structures as Lavinia Planitia, Sedna Planitia, and Aino Planitia.

The paleodirection and paleointensity of the geomagnetic field are determined from seven andesibasalt–basalt samples of three lava flows (L1–L3) from the Avachinskii (Avacha) volcano. Based on the sample from the recent lava flow TFE-50 (Tolbachik Fissure Eruption), the reliability of the Thellier–Coe method for geomagnetic field paleointensity determination is demonstrated: the deviation of the calculated H_an from the IGRF12 values is at most 3% with a quality factor q > 13. The age of lava flows L1–L3 is refined using paleomagnetic data. Flows L1, L2 of the Molodoi Cone were formed in 1827 and 300–600 years ago, respectively, and the age of flow L3 at the crest of the somma is determined at 30–32 ka, which agrees with the known age estimate of the debris avalanche associated with the catastrophic destruction of the Avachinskii volcano 29 900 ± 37 900 ¹⁴C years ago.

Abstract—Stability of a heavy inclusion in the Earth’s upper crust is studied by the linear theory method for small perturbations. The presence of such inclusions with an increased density is associated with chemical inhomogeneity or phase transformations. The stability problem of a heavy elastic layer above a less dense elastic layer representing the lower crust and mantle lithosphere is solved. It is shown that such a system is stable: small initial perturbations produce low-amplitude oscillations. The corrections of oscillation frequencies for the density jump at the boundary between the layers are calculated. The changes introduced to the solution by the consideration of creep, which is present even in cold geomaterials, are discussed. Creep causes instability of heavy inclusions in the upper crust. However, due to the very high effective viscosity of the cold upper crust, this instability is of a formal nature, since it develops so slowly that heavy inclusions in the upper crust hardly change their position on timescales comparable to the age of the Earth.

Abstract—It has been observed that strong earthquakes and volcanic eruptions are sometimes followed by geomagnetic oscillations with frequencies of 3.5–4.0 mHz. This paper describes the theoretical study of the probable cause of these phenomena, which is related to the vertical acoustic resonance between the Earth’s surface and the thermosphere, produced by the propagation of the atmospheric wave corresponding to the acoustic branch generated by surface displacements. The propagation of two-dimensional (2D) harmonic acoustic wave is analyzed in a plane layered model of the atmosphere and ionosphere with oblique geomagnetic field. The altitude of the reflecting atmospheric layer corresponds to the region of a sharp temperature change in the vicinity of the thermosphere boundary ~80–90 km. The calculated fundamental resonant frequency is close to the observed oscillations. The obtained solution is used to calculate currents and electromagnetic perturbations in the atmosphere and ionosphere. Assuming thin-layer approximation for the ionospheric E-layer, we derive formulas describing the geomagnetic disturbances (GMD) in the ionosphere and on the Earth’s surface. The GMD spectrum has a sharp peak at the frequency corresponding to the acoustic resonance. According to the calculations, close to the resonance frequency, the power spectral density of GMD on the ground can reach 5–30 nT²/Hz, which is consistent with the results of ground-based measurements.

Abstract—There are regions of moderate seismicity that have long lacked a dense network of seismic stations due to their sparse population, inaccessibility, and low economic levels. Characterization of earthquakes in such regions is typically limited to scarce macroseismic information available and data from only one or two seismic stations. Most often, the location of these earthquakes was based on the use of macroseismic information alone. We propose a method for probabilistic estimation of the location of such earthquakes based on a joint analysis of their macroseismic and instrumental data. The technique is implemented in the ProLoM program (Probabilistic Locator by Macroseismics). In this study, we test the performance of the method on a test earthquake of May 20, 1967 and present the analysis results for the earthquakes that in the north of the East European Platform that occurred on June 30, 1911 and January 13, 1939.

Abstract—A model of a double-porosity medium with damageable matrix subject to anomalously high formation pressure is discussed. It is assumed that damage in the matrix enhances mass transfer between the subsystems of the medium. The problem about the coupled fracture and fluid flow process in a fractured-porous medium in one-dimensional (1D) statement is solved numerically. The limited spatial extent of the zone of hydraulically conductive fractures is taken into account.