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Long-period (10

We consider results of magnetotelluric and magnetovariational soundings in the period range 10<T much less than 20000 s in the North Vietnam area. The simple structure of magnetovariational responses is shown, which generally reflects the electrically conductive quasi-two-dimensional structure of the Earth's crust. Impedance responses form as a superposition of responses of local complex subsurface and quasi-two-dimensional regional deep-seated structures. Separation of local and regional effects made it possible to construct a geoelectrical depth model of the regional tectonosphere, whose main elements are electrically conductive subvertical trans-lithospheric faults and high-resistivity disturbances of the conductive asthenosphere. These elements, favoring the flow of telluric currents induced in deep-seated electrically conductive systems into the sedimentary cover, form zones of abnormal apparent-resistivity curves. The apparent resistivity monotonously increases with increasing the period up to 20,000 s. We called the combination of such elements of the geoelectrical model a ultradeep fluid-fault system (UDFFS). The modeling has established the location of three orthogonally intersecting UDFFS of NE and SE strikes in the North Vietnam area. It shows that conductive (fluid-saturated) translithospheric faults extending to the base of the sedimentary sequence control the location of petroleum fields and ore deposits. A method for separating local and regional magnetotelluric effects is proposed. It permits one to determine reliably the main strikes of a regional two-dimensional structure and the configuration of the apparent-resistivity curves along them.

ISSN: 1068-7971
Serial Title: Russian Geology and Geophysics
Serial Volume: 61
Serial Issue: 9
Title: Long-period (10<T<20,000 s) magnetotelluric studies in northern Vietnam
Affiliation: Russian Academy of Sciences, V. Il'ichev Pacific Oceanological Institute, Vladivostok, Russian Federation
Pages: 1036-1055
Published: 202009
Text Language: English
Publisher: Allerton Press, New York, NY, United States
References: 31
Accession Number: 2021-006938
Categories: Applied geophysicsSolid-earth geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, sketch maps
N19°00'00" - N22°00'00", E104°00'00" - E108°00'00"
Secondary Affiliation: Russian Academy of Sciences, Schmidt Institute of Physics of the Earth, RUS, Russian FederationRussian Academy of Sciences, Yu. Kosygin Institute of Tectonics and Geophysics, RUS, Russian FederationVietnam Academy of Science and Technology, VNM, Vietnam
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2021, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 202105
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