STRUCTURE OF THE EARTH'S CRUST IN THE LENA RIVER DELTA: NEW COMPREHENSIVE GEOLOGICAL AND GEOPHYSICAL DATA
E.V. Deev1,2, A.A. Duchkov1,2, L. Yu. Eponeshnikova1, P.A. Dergach1,2, A.A. Zaplavnova1, V.V. Potapov1,2, O.V. Safronov1,2, S.N. Ponasenko1,, R.M. Tuktarov3, S.V. Shibaev3
1 Trofimuk Institute of Petroleum Geology and Geophysics of SB RAS, Novosibirsk, Russia
2Novosibirsk State University, Novosibirsk, Russia
3Yakutsk branch of Federal Research Center Geophysical Survey of RAS,Yakutsk, Russia
Keywords: Earthquakes, active fault, local seismology, seismic tomography, magnetotelluric soundings, Earth's crust, Siberian craton, South Laptev rift, Verkhoyansk fold-and-thrust belt, Lena River delta
Abstract
The paper presents a comprehensive analysis of new geological and geophysical data for the Lena River Delta region in order to clarify the structure and interaction between the Siberian Craton, the Verkhoyansk fold-and-thrust belt, and the Laptev Sea rift system. New geophysical data include the local seismic monitoring (613 earthquakes for the period of 2018-2024) and the magnetotelluric sounding measurements (MTS, 21 points). Here we present the results of the joint interpretation of morphostructural data, seismic tomography, MTS, and gravity anomalies. Seismic activity is migrating is migrating from year to year but always confined within the crustal structures of the Verkhoyansk fold-and-thrust belt and the South Laptev rift. Seismic-tomography results reveal two-layer structure of the upper crust from the South-West side of the study area. The upper layer (high Vp/Vs ratio) is 15-20 km thick and it corresponds to the structures of the Verkhoyansk fold-and-thrust belt and the South Laptev rift overlaying the Northern edge of the Siberian craton. The lower layer (low Vp/Vs ratio) corresponds to the Precambrian crystalline basement of the Siberian craton. This two-layer crustal model is traced beneath the deltaic sediments of Lena River to the northeast for approximately 30 km, after which we see only one layer with high Vp/Vs values. MTS data provide us with more details on the structure of the upper part of the crust. This structure is consistent with the presence of the South Laptev rift between the Bulkur and Bykov faults, as well as with the presence of the Tumat horst to the northeast from the Bykov Fault. Modern fault activity is recorded by subvertical low-value anomalies of specific electrical resistance from MTS data (fluid-saturated zones) and zones of earthquake-hypocenter concentration, which is observed for the Bulkursky, Nizhnelensky, Bykovsky, and Sardakh faults.
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