Comparative Assessment of the Manifestation of Seismicity within the Southwestern Part of the Baikal–Mongolian Region for Various Seismic and Ground Conditions of Construction

Abstract

The intensively developed densely populated parts of the Baikal–Mongolian region (BMR) within the Selenga River basin and the southwestern part of the Baikal seismic zone have been selected for research. Geomorphologically, the territory is located within the Selenga Dauria, which merges with the mountain ranges of Mongolia. Earthquakes constantly occur here, and their strength varies widely, sometimes reaching catastrophic values. The high seismic potential of the region is due to the presence at a relatively short distance of seismically active zones in the north (Lake Baikal) and in the south (Mongolia) and the presence of earthquake epicenters with an energy class reaching 15. The main tectonic elements of the area are the faults that control the Meso-Cenozoic depressions. Fragments of these faults correspond to the zones of occurrence of earthquakes with a magnitude of 5.5–6.0. Therefore, the study of the seismic process, the features of the manifestation of seismicity, and the assessment of the seismic hazard of this territory are currently given special importance. The research results are aimed at developing methods for studying and predicting the seismic effects of large earthquakes in the BMR. As a result, the most probable seismic-soil models are formed for various thicknesses of loose deposits, differing in their composition and state, taking into account the depth of bedrock occurrence. The available seismogeological and geophysical information and the data obtained by us on the study of engineering and seismological conditions for the construction of a number of industrial and civil facilities are used. According to the records of the last large earthquakes by permanent seismic stations, a single initial signal was formed for the accepted level of initial seismicity. When using it for the constructed models and implementing theoretical calculations, a comparative analysis of the effect of near-surface inhomogeneities on the initial seismic signal was carried out using a set of main indicators of seismicity manifestation: seismic characteristics (accelerograms, spectra, and frequency characteristics) and their parameters (maximum accelerations and prevailing and resonant frequencies). The data presented for the prevailing varieties of soils of various conditions lead to the possibility for their use in zoning the seismic hazard of the study area.