Geophysical research: article

Analysis of hodographs for the southern part of the Altay-Sayan foldеd area based on records of industrial explosions
T.A. Tushko1
V.I. German2,3
1 Siberian Federal University SFU, Institute of Space and Information Technology, Krasnoyarsk, Russia 2 Krasnoyarsk Research Institute of Geology and Minerals, Krasnoyarsk, Russia 3 Institute of the Earth’s crust SB RAS, Irkutsk, Russia
Journal: Geophysical research
Tome: 23
Number: 1
Year: 2022
Pages: 62-76
UDK: 550.34
DOI: 10.21455/gr2022.1-5
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Keywords: velocity model of the medium, hodograph, seismic station, seismic ray, time residual, refracted wave, head wave, hypocenter
Аnnotation: Currently, a local seismic network has been deployed on the territory of Tyva, Khakassia and the south of the Krasnoyarsky krai, which allows to record weak seismic events that were previously inaccessible for research. During observations many artificial seismic sources with known coordinates – industrial explosions – were recorded. Using the highest quality records, the task was set to compare and analyze the hodographs that define the velocity structure of the environment in the region. This article discusses the hodograph that is currently used for the location of seismic events and the new regional hodograph proposed by the authors. This hodograph was calculated on the basis of the previously constructed block-layered velocity model of the medium using an algorithm based on analytical solutions of the direct kinematic seismic problem in the medium with linear dependence of velocity on depth. Calculations were made with a step of 5 km in depth and epicentral distance; the introduction of station corrections to the hodograph for low velocity zones under seismic stations and their excess above sea level was planned. A preliminary comparison of the hodographs indicates a deeper position of the Moho boundary in the accepted model of the medium and an increase in velocity with depth within the Earth's crust at a lower initial value. For the analysis of hodographs, 37 explosions with the highest magnitudes recorded by seven seismic stations were selected. A total of 119 seismic rays were considered. For all rays, the time residuals between the experimental moments of wave arrival at the seismic station and the predicted ones, taken from the travel time curves under consideration, are calculated. The comparison results are summarized in two tables. The first table shows the residuals obtained from the data of one randomly selected source. The second includes all experimental material, statistically processed to eliminate the effect of random errors. The comparison shows that the level of time residuals between the experimental times and those took from the new hodograph is less than those for the current hodograph for almost all seismic stations. In addition, there is no increase in the level of residuals with an increase in epicentral distance, which is typical for the current hodo-graph. This confirms the authors’ assumption that the model for the new hodograph better reflects the velocity structure of the medium of the area controlled by the seismic network. Thus, based on a comparative analysis of residuals characterizing the degree of correspondence of hodographs to the real environment, one can conclude that new regional hodograph is promising for data processing tasks from local and nearby seismic events and earthquakes in the seismically active region, including the south of the Krasnoyarsky krai, Khakassia and Tyva.