SEASONAL VARIATIONS OF SPECIFIC ELECTRIC RESISTIVITY
IN UPPER LAYERS OF THE EARTH CRUST
A.V. Desherevskii1, I.N. Modin2, A.Ya. Sidorin1
1 Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, Moscow, Russia
2 Lomonosov Moscow State University, Moscow, Russia
Corresponding author: A.Ya. Sidorin, e-mail: al_sidorin@hotmail.com
Abstract. For predicting the effects of strong earthquakes, it is important to know the ground characteristics. In the usual methods of such an assessment, the fact is ignored that the ground properties can vary greatly during the year. This is due to the lack of data required for such accounting. In this paper, using the example of the analysis of long-term VES monitoring data on a stationary line array with a large number of spacings, we study seasonal variations in electrical resistivity at different depths in the near-surface part of the section in the area of Peter the Great Range in Tajikistan. According to the data of long-term precise daily measurements, a 4-layer horizontal-layered model of the geoelectrical section was constructed. The amplitude of seasonal variations in specific resistivity in each layer was estimated as the ratio of the standard deviation of seasonal variation to the multiyear average of specific resistivity. In the upper part of the section (depth 0–1.5 m), the amplitude of the seasonal variation reaches up to 20%, and its shape agrees well with the seasonal variation of apparent resistivity at small spacings. In the second (depth 1.5–10 m) and third (depth 10–66 m) layers of the geoelectric section, the amplitude of the seasonal wave decreases rapidly, being less than 1% in the third layer. In the fourth layer of the geoelectric section (depth from 66 m and more), the amplitude of the seasonal changes increases again and reaches 2%. In this case, the difference between the maximum and minimum values of the seasonal wave (i.e., its range) reaches 7%. One of the possible explanations for such a high amplitude of seasonal variations in specific resistivity at depths of hundreds of meters is the presence of a deep aeration zone with annual regulation of the level and salinity of groundwater. The obtained results must be taken into account in exploration geophysics, in engineering surveys and taking into account the properties of soils when predicting the possible consequences of strong seismic effects.
Keywords: shallow structure, electrical resistivity, seasonal changes, ground properties, effect on seismic load estimates, precise geoelectric monitoring, vertical electrical sounding, inverse problem solution, horizontal-layered model, Garm research area
Cite this article as: Desherevskii A.V., Modin I.N., Sidorin A.Ya. Seasonal variations of specific electric resistivity in upper layers of the earth crust, Voprosy Inzhenernoi Seismologii (Problems of Engineering Seismology), 2018, Vol. 45, No. 3, pp. 68–83. [in Russian]. DOI: 10.21455/VIS2018.3-6
English translation of the article will be published in Seismic Instruments, ISSN: 0747-9239 (Print) 1934-7871 (Online), https://link.springer.com/journal/11990), 2019, Volume 55, Issue 3.
About the authors
DESHCHEREVSKII Alexey V. – Cand. Sci. (Phys. and Math.), leading researcher, Schmidt Institute of Physics of the Earth, Russian Academy of Sciences. Moscow, Russia. Tel.: +7 (499) 254-90-35. E-mail: adeshere@ifz.ru
MODIN Igor N. – Dr. Sci. (Tech.), professor, Lomonosov Moscow State University. Moscow, Russia. E-mail: imodin@yandex.ru
SIDORIN Alexander Ya. – Cand. Sci. (Phys. and Math.), head of laboratory, Schmidt Institute of Physics of the Earth, Russian Academy of Sciences. Moscow, Russia. Tel.: +7 (499) 254-42-68. E-mail: al_sidorin@hotmail.com