Izvestiya, Physics of the Solid Earth最新文献

Abstract—

The results of the long-term gradient magnetic measurements performed in the southwest part of Baikal as supplementing the experiment on deep-water monitoring of the electric field vertical component, can be applied to study the deep geoelectric section. Baikal cannot be approximated by a two-dimensional model in the region under study. Therefore, a three-dimensional geoelectric model of the lake and adjacent territories was constructed based on the existing geological and geophysical data. However, these data are insufficient for the region where our observations are carried out. Refinement of the section upper part based on the magnetic field gradients on long bases has been performed using the neural network inversion method. Then, proceeding from the obtained basic model, alternative models were developed, which reflect the known hypotheses about the structure of the deep part of the Baikal rift section: mantle diapir and asthenospheric upwelling. The phase differences between the base-averaged field gradient and the field itself at the base site, as well as the phase differences on the ends of this base, as the most noise-proof gradient functions, are calculated for them. Based on comparison of the experimental and model frequency curves, it is concluded that the mantle diapir model fits best the experimental data, at least, in the southwest part of the Baikal rift zone.

Abstract—In situ electrical resistance measurements are performed on samples of iron with a hexagonal close–packed lattice (ε-Fe), compressed and heated by stepwise shock loading. Equations of state for ε-Fe are constructed. The obtained experimental results are mathematically simulated in the hydrocode based on the developed equations of state. The modeling results are used to reconstruct the volume temperature dependence of the ε-Fe electrical resistivity at pressures of ≈20–70 GPa and temperatures of ≈750–950 K. The volume–temperature dependence of the ε-Fe thermal conductivity coefficient is calculated according to the Wiedemann–Franz law. The results obtained for the electrical and thermal conductivity of shock compressed and heated ε-Fe are compared with literature experimental and theoretical data for iron and silicon iron.

Abstract—The response of sandy and clay subsurface soils, representing classes of non-cohesive and cohesive soils, during seismic motion of various intensities is analyzed based on the in situ observations—records by seismic vertical arrays of the Japanese strong motion network KiK-net. From a total of ~800 stations, five stations with sandy and five stations with clayey subsurface soils represented in the upper layers in their purest forms were selected for the analysis. For sandy and clayey stations, models of soil behavior during strong motion were constructed by the method of (Pavlenko and Irikura, 2003), showing vertical distributions of stresses and strains induced by strong motion in soil layers; and the behaviors were compared. Similar estimates of the amplification of seismic waves in sands and clays during weak motions and similar stress-strain relations describing the behavior of subsurface soils during moderate seismic motions are obtained. The liquefaction of sandy soils during strong motions (the 2011 Tohoku earthquake, Mw ~ 9.0) and the effects of extended seismic source (the directivity of seismic radiation) on the behavior of sandy and clayey soils and amplification of seismic waves are analyzed. Differences in the behavior of sandy and clayey soils are observed only during strong motions, namely, liquefaction occurs in sandy soils (when the groundwater level is about several meters from the surface), but never in clayey soils.

Abstract—The geomechanical modeling of the stress-strain dynamics before the 2019 M = 7.1 Ridgecrest earthquake, Southern California, revealed an alternating pattern of maximum displacement anomalies that develop around the ends of the future rupture, simulating the process of “swinging” in the epicentral zone of the earthquake. These results, together with the existing theoretical concepts of crustal block structure with block interaction, are used to build a “swing” geomechanical model based on the stick-slip phenomenon in a three-block configuration. The parameters of the model are related to the rheological properties of the Earth’s crust in the area of destruction of the bridging isthmus (a patch), which determines the source size of the seismic event.

Abstract—A series of magnetotelluric and seismic studies have been carried out on profiles covering more than two thousand kilometers within the North Caucasus region. The earlier interpretation of the magnetotelluric observations by means of one– and two–dimensional inversion and three–dimensional mathematical modeling software has helped to construct a series of sections and models which are viewed as test and starting ones for the construction of a three–dimensional geoelectric model of the region. The test models have been used to test how well the software for three–dimensional inversion of the impedance tensor components in the magnetotelluric sounding method can estimate the parameters of conducting blocks in the structures of the Greater Caucasus and the Scythian plate. In the resulting geoelectric model, constructed from the results of three–dimensional inversion of all impedance tensor components, the position of low–resistance blocks correlates with deep faults, volcanoes of various genesis, and seismically active zones characterized by the reduced velocity of seismic waves and their increased absorption. The electrical resistivity of low–resistance anomalies is explained by the degree of their saturation with the fluid water fraction. Its maximum concentration is found within the intersections of fault systems, flexural–rupture zones, and deep faults activated by tectonic processes.

Abstract—We have investigated nearly all of the currently available hydromagnetic survey data to study the magmatic structures in the sedimentary basin of the Barents Sea region. We use the modern interpretation techniques to process over 93 000 km profile data of 1995–2017. It was established that north-west striking dyke groups are abundant in the central and northern parts of the basin; in the south part no dykes were found. Magmatic structures in the sedimentary basin are reflected by the local magnetic anomalies of two types—the linear ones sourced by dykes, and mosaic ones associated with the local areas of magmatism. At sea depth of 100–500 m and sediment thickness over 8 km, the dominant depth of the upper edges of the bodies generating anomalies is about 1500 m. The analysis of the magnetic anomalies could help us to outline more exactly the sedimentary structures, the history of the magmatic processes and the tectonic evolution of the Barents Sea Region.

Abstract—The vertical movements measured by broadband seismic stations located around the epicenter of the December 26, 2004 Sumatra 2004 mega-earthquake of magnitude 9.1 are analyzed. It is shown that during the five years before the earthquake (1996 to 2000), the COCO station closest to the epicenter, located 1700 km away, recorded quiet daily variations. Step-like distortions in the level of the recorded seismic noise appeared at this station in 2001 and continued up to the time of the earthquake. The station has also recorded pulses lasting a few minutes, with amplitudes gradually increasing to several times the amplitude of diurnal variations, followed by a decrease. The pulses occurred under quiet meteorological and geomagnetic conditions. No such pulses were found in the records of stations more than 2000 km from the epicenter. It is hypothesized that the sharp changes in the low-frequency seismic noise reflect tectonic slips on the faults in the lithosphere of the Indian Ocean.

Abstract—Numerical reconstructions of the thermal regime of the lithosphere of the West Siberian basin in the Koltogor-Urengoi graben in the vicinity of the Tyumen SG-6 superdeep well are used to analyze the depth distribution of thermal conductivity of basin rocks. Five depth intervals that differ in the pattern of changes in thermal conductivity of rocks are distinguished: permafrost zone, sedimentary section below this zone, zone of anomalous decompaction of rocks, consolidated crust, and mantle. The algorithms for calculating thermal conductivity are considered, and the main factors affecting the depth changes of the latter are determined for each of the five intervals. A sharp decrease in thermal conductivity of rocks at the base of the sedimentary cover and at the basement top in the vicinity of the SG-6 well is associated with rock decompaction due to tectonic fracturing and hydrothermal erosion. The analysis suggests that the stationarity conditions of the process are not observed in optical scanning thermal conductivity measurements and, therefore, this method may overestimate the true thermal conductivity of rocks.