GEOELECTRIC PATTERNS OF ACTIVE FAULTS IN PERMAFROST REGIONS (ON THE EXAMPLE OF HIGH-MOUNTAIN AND ARCTIC RUSSIAN REGIONS)
E.V. Deev1,2, V.V. Olenchenko1,2, A.A. Duchkov1,2, A.A. Zaplavnova1, O. V. Safronov1,2
1Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences,Novosibirsk, Russia
2Novosibirsk State University, Novosibirsk, Russia
Keywords: electrical resistivity tomography, active faults, permafrost, Gorny Altai, Lena River delta
Abstract
Using the example of active faults in the high mountainous part of the Gorny Altai (South Chuya and Kubadu fault zones) and the Lena River delta (Primorsky Fault Zone), active fault zones in the conditions of permafrost development were studied using the electrotomography technique. The method was shown to be effective in identifying active fault zones to depths up to the first hundred metres in permafrost conditions. However, the presence of icy rock with a resistivity greater than 100 kOhm·m limits its application due to the shielding effect of the insulating layer. The main criterion for identifying active faults in geoelectrical sections are subvertical zones of reduced resistivity against a background of high resistivity permafrost layers. This concerns both relatively young seismic ruptures formed during the Chuya earthquake (Ms=7.3) 27.09.2003 in the South Chuya Fault Zone and more aged Holocene fault scarps in the zones of the Kubadru and Primorskiy faults. At the same time, resistivity values in the zones of active faults and seismic ruptures are too high to assume their saturation with free water. The decrease in resistivity in such zones relative to the host permafrost frame may be due to: 1) increased rocks and sediments fracturing; 2) occurrence of thinly fractured material in the core fault zones, including in cracks, where physically bound non-freezing water is concentrated; 3) residual thermal anomalies in the case of modern activations, so that negative temperatures have already been restored, but the process of frozen strata degradation is not fully completed yet; 4) saturation of the geological section with sandy-silty material as a result of the development of liquefaction and fluidization processes during earthquakes. The revealed regularities can be used not only to confirm the zones of morphologically distinctive segments of active faults, but also to search for their buried segments in the areas of permafrost development typical for seismically active high mountain and Arctic regions of Russia and worldwide.
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