Gravity Anomalies, Fault Tectonics and Seismicity of the Terek-Caspian Trough

Abstract

Relevance. When studying the geological structure of deeply submerged oil and gas promising horizons and studying the modern geodynamics of the Terek-Caspian trough (TCT), it is very important to clarify the spatial position of the existing fault structures and identify new ones. To determine the spatial position of the faults, a set of geological and geophysical criteria is established, with geophysical features prevailing. Aim. Based on the gravity anomaly map of scale 1: 200,000 and magnetic field maps of scales 1: 200,000 and 1: 500,000, digital models of gravitational and magnetic fields were created and a diagram of the anomalous gravitational field (Δga) of the western part of the TCT was drawn. The electronic database of seismological information was compiled on the basis of information about historical and instrumental earthquakes (1950–2020), as well as macroseismic data. Methods. The transformation of the initial anomalous gravitational field is performed by calculating the horizontal gradient vector Wsz and the third vertical derivative Wzzz of the gravity potential using a computer program that implements the F-approximation method based on the representation of the potential of the anomalous gravitational and magnetic fields by the Fourier integral. To analyze the seismicity, the seismic activity А10 was calculated according to the formula of Yu.V. Riznichenko using a computer program that implements the summation method with constant detail, based on the summation of the number of earthquakes of all energy classes greater than the minimum representative in a fixed averaging zone. Results and discussion. Based on the results of processing and interpretation of geophysical data, a set of thematic maps was built for the TCT territory. This set includes maps of the horizontal gradient vector Wsz and the third vertical derivative Wzzz of the gravity potential; seismic activity map А10. Based on the analysis of the data obtained with the involvement of existing geological information, the position of the known faults was clarified and new ones were identified, based on the results of the research, a map of the faults for the western part of the TCT was compiled.