Russian Journal of Earth Sciences

The paper presents analysis of intra-centennial (inter-decadal and multidecadal) variations of the length of day (LOD) and some oceanic parameters such as sea surface temperature (SST) and sea level (SL). Methods of multivariate regression analysis and correlation analysis are used. Results of the regression analysis show a spatially coherent response of SST to LOD variations on the multidecadal time scale. The earlier response is peculiar to the north and tropical Atlantic where the multidecadal SST variations are approximately opposite to the LOD variations. In the most remaining parts of the oceans, except especially in the Nino 3.4 region of the equatorial east Pacific, the multidecadal SST variations are generally lagged relative to the antiphase variations of the LOD. Smoothing of SST averaged over different areas and of the global mean SL shows that the intra-annual variations include inter-decadal, 20–30-year, multidecadal, 60–70-year, components that correspond to similar oscillation components in the LOD. The most striking correspondence of the two components is observed between the LOD and SST averaged over the Nino 3.4 region. Generally, there are significant correlations of the intra-centennial variations on the averaged and smoothed SST series and global mean SL with the LOD variations. We propose that angular momentum exchange processes involving oceanic circulation and interactions between the Earth’s core and the mantle play probably a part in the observed relationships of intra-centennial variations in oceanic parameters with variations in the LOD.

The Baikal Rift Zone is seismically active and each well recorded strong earthquake (for example, as the Kultukskoe earthquake (South of Baikal), on August 27, 2008, with Mw = 6.3) is the reason to refine existing models for seismic hazard estimates. There are several approaches to study strong ground motion, and one of them is to model synthetic accelerograms to reconstruct the rupture process. In this paper we are mostly interested in calculating accelerograms for the city of Irkutsk, considering source spectra with two corner frequencies, primarily, to reconstruct impact from the Kultukskoe earthquake.

In earth dams, a permanent filtration of water leads to washing out of sand-clay fraction and to a formation of soil decompression sites, which pose a danger to embankment integrity. Condition monitoring of earth hydraulic structures can be executed by geophysical methods. The article presents the results of geoelectric monitoring conducted on the dam of settling pond of mine water with high metal content. The investigations were carried out by vertical electrical soundings, including electrotomography, and by methods of induced polarization in time and frequency domains. According to the results of the electrical soundings, places of reduced soil resistivity in the dam were identified, associated with infiltration of precipitations and of water from the pond. Geoelectric monitoring showed changes of the soils resistivity in different years, depending on hydrological conditions. Induced polarization methods are sensitive to material composition of soils, such as clayiness and presence of electronically conductive minerals. It is determined that the highest content of clay is in the upper and middle parts of the embankment. In eastern part of the dam, intensive polarizability of the medium was detected. It can be caused by filtration of water, contaminated with metals, through the embankment and sedimentary rocks. Thus, by resistivity measurements, it is possible to identify areas of intensive filtration in the dam body, and induced polarization measurements make it possible to determine clay content in the soil and possible pathways of contamination through the dam, which is of great importance for studying the environmental situation of region.

The identification of faults is a common objective in geophysical potential field methods. Vertical discontinuities such as reverse faults, also known as tectonic faults, can easily be distinguished through their effect on gravity and magnetic fields, appearing as gradient zones or areas of change in the field. However, identifying strike-slip faults is one of the biggest challenges for potential field methods as they are characterized by a complex series of anomalies with varying signs in the fault zone, as well as displacement of anomaly axes between the strike-slipped blocks. The goal of this study is to suggest a transformation that would aid in the identification of shear zones through the calculation of the displacement along the discontinuity. The proposed approach involves calculating the correlation coefficient between parallel profiles using moving windows. The position of the window with the highest calculated correlation coefficient allows estimating of the discontinuity displacement magnitude. The method was tested using a synthetic field and data from the magnetic field of the Kolbeinsi Ridge.