Statistical characteristics calculation of seismic intensity increments for the purpose of seismic microzoning in mountain territories
Authors:   Vladikavkaz Scientific Center of the Russian Academy of Sciences, Zaalishvili Vladislav , Kambolov Dzambolat ,   North Caucasian Institute of Mining and Metallurgy (State Technological University), Melkov Dmitry ,   Vladikavkaz Scientific Center of the Russian Academy of Sciences, Fidarova Madina ,   Vladikavkaz Scientific Center of the Russian Academy of Sciences
Published: May 2024

Introduction. During seismic micro-zoning of a territory, one of the main instrumental methods for calculating intensity increments is the registration of earthquakes in areas with different soil conditions. In this case, the calculation of increments is based on the amplitudes of oscillations simultaneously in the given and reference sections. The purpose of the work is to compare the increments in various expressions obtained for powerful vibration and pulse sources, as well as for an instrumental measure of seismic intensity. Materials and methods. Processing of instrumental data, their systematization and description using basic statistical indicators. The analysis was carried out using data from the Vladikavkaz network - records of earthquakes obtained simultaneously at four seismic stations located in areas with different ground conditions. Results. To check the formulas for calculating seismic intensity increments and comparing them with the obtained data, distribution histograms and the corresponding probability density functions were constructed, under the assumption that the distribution is normal. All methods for calculating vibration amplitudes gave identical results in ranking areas according to the degree of seismic hazard, however, taking into account rounding, an increase in intensity by 1 point is not always achieved in an area where, due to the worst soil conditions. The best results for calculating intensity increments were obtained for the area values of the velocity and acceleration spectra. At the same time, the areas of the acceleration spectra provide better differentiation of soil conditions according to the degree of danger (with the same coefficient in front of the logarithm). Discussion. The task of developing an instrumental method of seismic micro-zoning is to clarify the coefficients in front of the logarithmic scale of the quantities under consideration, the reduction of which, in turn, determines the clarification of the level of impacts for given intensities. On the other hand, smaller coefficients lead to worse differentiation of soil conditions of areas when calculating increments of seismic intensity. The solution to the problem may lie somewhere at the junction of both approaches. Conclusion. Analysis of the results shows a connection between the magnitude of the distribution dispersion and the complexity of the engineering-geological conditions of the site. The more factors influence the wave processes in the soils, the greater the scatter of values around the average. Main factor is a multi-layered environment, i.e. the presence of reflective boundaries, and the other one is the very properties of the medium, i.e. its dispersion. Resume. Results are useful in differentiating soil conditions by an additional parameter that affects the probability of failure to exceed the calculated values of seismic impacts - the same average values of seismic intensity can be characterized by different confidence intervals; from a practical point of view, one should set the same probability of not exceeding the design impact values. Suggestions for practical applications and directions for future research. For practical applications it is necessary to distinguish the influence of the layering of the medium and the direct dispersion of the soils composing the stratum, which represents the next research task.