A Joint Analysis of Seismicity and the Results of Modeling of Geodynamics to Assess Seismic Hazard with Application to the Altai-Sayany-Baikal Region

RFBR project (20-05-00171) Project leader D.Sci. A.A. Soloviev

The urgency of the problem of reducing damage from earthquakes is constantly increasing due to the increase in population density, an increase in the technogenic load on the natural complex and the development of environmentally hazardous industries. One of the ways to solve this problem is to improve the existing and develop new methods for an adequate assessment of seismic hazard. Taking into account the multifactorial nature of the processes leading to earthquakes, such an estimate can be obtained only through the use of a complex of methods. Within the framework of the project, three approaches are applied: (1) recognition of strong earthquake-prone areas based on morphostructural zoning; (2) modeling the dynamics of block and fault structures and seismicity; (3) assessment of seismic hazard based on the use of both data (instrumental and historical) about real earthquakes and earthquakes obtained as a result of modeling. The final goal of the project is to obtain, based on these approaches, seismic hazard assessments for the Altai-Sayany-Baikal region. During the reporting year of the project, the focus was on the first approach. As a result, the map of morphostructural zoning (MSZ) of the Altai-Sayan-Baikal region was refined, the places of possible occurrence of strong (with a magnitude M >= 6.0) earthquakes in this region were identified, the reliability of the recognition results was checked using control experiments, and geological and geophysical features of places where strong earthquakes are possible were obtained. The MSZ map shows the hierarchical block structure of the region, the network of morphostructural lineaments that bound the blocks, and the positions of the nodes formed around the intersections of the lineaments. Based on the description of the nodes by a set of uniformly measured geological and geophysical characteristics using the pattern recognition algorithm, seismogenic nodes D, capable of generating earthquakes with M >= 6.0, were identified among all nodes. The result of recognition is a recognition rule that allows one to recognize nodes D among the entire set of nodes, and the actual division of nodes in accordance with this rule into two separate classes: seismogenic D-nodes and N-nodes, in which events with M> = 6.0 are unlikely. In the region under consideration, a total of 97 nodes have been identified, which are divided into 33 D-nodes and 64 N-nodes. So far, earthquakes with M>=6.0 have not been recorded at 17 D-nodes. These seismogenic nodes are located on high-rank lineaments separating the main morphostructures of the region. The high seismic potential of some of these nodes is confirmed by paleoseismic results obtained in the region by other researchers.

Morphostructural map of the Altai-Sayan-Baikal region and seismogenic nodes recognized in the region.

Continuous lines mark the longitudinal lineaments, dashed lines depict the transverse lineaments. Bold lines show the lineaments of the 1st rank, middle lines mark the lineaments of the 2nd rank, hairlines depict the lineaments of the 3rd rank. Red dots depict epicentres of earthquakes with M ≥ 6. Circles depict nodes capable of earthquakes with M ≥ 6.