DETERMINING THE STRESS FIELD IN EARTH'S CRUST FROM SOURCE MECHANISMS OF LOCAL EARTHQUAKES IN THE TRANSCARPATIANS

The article summarizes the results of research aimed at study the possible reactivation of the fault system in the Earth's crust of the South China Sea with likely dangerous consequences for the coastal area of Vietnam. The research was carried out over several years with the publication of interim results. The solution to this problem required the determination of the regional stress field in the Earth's crust. Analysis of the focal mechanisms of local earthquakes, as well as the structural characteristics of faults, obtained by gravity and seismic data, was used for this. The possibility of renewal of fault activity was determined by the inversed-stress method in the calculated regional stress field. The parameters of the present-day stress field were used to estimate the required slip force along the pre-existing faults. To assess the probability of reactivation of the entire system of faults, the possibility of horizontal and vertical structural (block) displacements in the Earth's crust of the study area was calculated. Based on a comprehensive analysis of the data obtained, a forecast was made of the probability of reactivation of the fault system in the South China Sea region. This can be the cause of earthquakes, underwater landslides and other geological hazards in the coastal area of Vietnam.

Download Full-text

Determination of energy parameters of seismic events of the Transcarpathian trough taking into account the quality factor of the Earth’s crust

Geofizicheskiy Zhurnal ◽

10.24028/gzh.v43i2.230201 ◽

2021 ◽

Vol 43 (2) ◽

pp. 218-226

Author(s):

Yu.A. Andrushchenko ◽

V.I. Osadchy ◽

O.I. Lyashchuk ◽

I.V. Kornienko ◽

M.I. Halabuda

Keyword(s):

Quality Factor ◽

Active Regions ◽

Seismic Wave Propagation ◽

Earth’S Crust ◽

Calibration Function ◽

Energy Parameters ◽

Local Earthquakes ◽

Earth's Crust ◽

Quantitative Indicators

Transcarpathia is characterized by significant differences in the structure and geodynamics of the lithosphere in comparison with other seismically active regions of Ukraine, which causes a number of features of the seismotectonic process of this region. The spatial distribution of the seismicity of the Transcarpathian Depression is closely related to the fault-block structure of the foundation. Important characteristics of the seismic process in Transcarpathia are the energy parameters of local earthquakes — magnitude, intensity, energy class. It is these values that form the basis of seismic zoning. The methods used to determine the energy parameters of local earthquakes do not fully take into account the effects of hypocenter depths and regional features of seismic wave propagation paths. Thus, the issue of determining the quantitative indicators of the quality factor of the Earth’s crust of the studied region and the development of approaches to determining the calibration function for estimating local magnitudes is relevant. The article presents the results of the study, which are aimed at determining the calibration function for calculating the energy characteristics of earthquakes in the Transcarpathian Depression, taking into account the parameters of attenuation of the Earth’s crust. Using digital records of seismic signals from the Transcarpathian Depression, obtained on the elements of the Ukrainian seismic group, as well as seismic stations «Stone Bridge», «Pidluby», «Zelenytsia» and «Lyubar» were determined quantitative indicators of the quality of the Earth’s crust and developed approaches to determination of the calibration function for estimation of local magnitude and its check on real signals.

Download Full-text