M. S. Kruglyakov

Novel accurate and scalable 3-D MT forward solver based on a contracting integral equation method

We present a novel, open source 3-D MT forward solver based on a method of integral equations (IE) with contracting kernel. Special attention in the solver is paid to accurate calculations of Greens functions and their integrals which are cornerstones of any IE solution. The solver supports massive parallelization and is able to deal with highly detailed and contrasting models. We report results of a 3-D numerical experiment aimed at analyzing the accuracy and scalability of the code. HighlightsNew 3-D magnetotelluric forward open source code is presented.The code shows very good performance in terms of accuracy and run time.Code accuracy is attained by a new scheme for estimating Greens function integrals.The implemented scheme of parallelization provides strong scalability of the code.

Electromagnetic sounding of the Kola Peninsula with a powerful extremely low frequency source

Experiment on electromagnetic sounding of the Kola Peninsula using unique mobile measuring complex of the low-frequency sounding was conducted, allowing to investigate a geoelectric section with a depth of several kilometers on distances up to 100 km from the stationary transmitting aerial. Excess on the order of amplitudes of the vertical component above the horizontal at all frequencies of sounding was registered in a number of points of measurements. This feature managed to be explained quantitatively by circulation of current on regional faults with the closure of current through the sea—before unknown galvanic coastal effect. Interpretation of the results of modeling and neural network solving of inverse problem essentially specifies the fault tectonics of the central part of the Kola Peninsula. Anomaly remote from the observation profile was found out—local pinch of a crustal conductive layer consisting of graphitized rocks and associated with the zone of overthrust.

The results of marine electromagnetic sounding with a high-power remote source in the Kola Bay in the Barents Sea

The first Russian six-component seafloor electromagnetic (EM) receivers were tested in an experiment carried out in Kola Bay in the Barents Sea. The signals transmitted by a remote high-power ELF source at several frequencies in the decahertz range were recorded by six receivers deployed on the seafloor along the profile crossing the Kola Bay. Although not all the stations successfully recorded all the six components due to technical failures, the quality of the data overall is quite suitable for interpretation. The interpretation was carried out by the three-dimensional (3D) modeling of an electromagnetic field with neural network inversion. The a priori geoelectrical model of Kola Bay, which was reconstructed by generalizing the previous geological and geophysical data, including the data of the ground magnetotelluric sounding and magnetovariational profiling, provided the EM fields that are far from those measured in the experiment. However, by a step-by-step modification of the initial model, we achieved quite a satisfactory fit. The resulting model provides the basis for introducing the corrections into the previous notions concerning the regional geological and geophysical structure of the region and particularly the features associated with fault tectonics.

Preliminary Results of Marine Electromagnetic Sounding with a Powerful, Remote Source in Kola Bay off the Barents Sea

We present an experiment conducted in Kola Bay off the Barents Sea in which new, six-component electromagnetic seafloor receivers were tested. Signals from a powerful, remote super-long wave (SLW) transmitter at several frequencies on the order of tens Hz were recorded at the six sites along a profile across Kola Bay. In spite of the fact that, for technical reasons, not all the components were successfully recorded at every site, the quality of the experimental data was quite satisfactory. The experiment resulted in the successful simulation of an electromagnetic field by the integral equation method. An initial geoelectric model reflecting the main features of the regional geology produced field values that differed greatly from the experimental ones. However, step-by-step modification of the original model considerably improved the fit of the fields. Thereby specific features of the regional geology, in particular the fault tectonics, were able to be corrected. These preliminary results open the possibility of inverse problem solving with more reliable geological conclusions.

On the computational methods in axisymmetric electrodynamics problems

The integral currents method is actively used at present to solve problems of electrical sounding. Its application requires calculation of the integrals of the kernel of an integrated equation and the function of conversion. In this work, the computational aspects of calculating such integrals for an axisymmetric case are considered, and a method that allows such calculations to be performed up to the asymptotic zone is proposed. The asymptotics of the conversion function are also studied.

Study of the possibility of the use of the magnetotelluric sounding method in the Arctic ocean with quantitative modeling

The task of the magnetotelluric (MT) sounding of the heterogeneous deep section of the Arctic ocean floor on the idealized model of gorst and graben lying on the typical oceanic, or continental Earth’s, crust is solved with the use of 3D quantitative modeling. In both cases, the sequence is covered by a layer of seawater with a thickness of 4 km. In this work, the difference in the MT sounding with the use of ocean-floor and surface equipment is considered. As a result, the conclusion was made that the floor equipment has a higher resolution than the surface equipment, in spite of the fact that the observations from the ice cover’s surface can be done more easily.

Prospects of magnetotelluric sounding in some large structures in the Arctic ocean

In the work, the results of modeling of electric resistivity distribution at the Gakkel and Alpha-Mendeleev underwater ridges are given. Based on the seismostratigraphic models, the apparent resistivity curves at a few points of the profile at the crossing of the ridge were constructed. The advantages and disad-vantages of the MT sounding method are presented. The results obtained can be used for future experiments.