PROBABLE EARTHQUAKE FOCAL ZONES SOUTHEAST OF KRASNOYARSK

This study investigates seismicity and seismically active structures of the northwestern Eastern Sayan. The relevance of the study stems from the need to reassess seismic potential of these structures after their associated M W=5.5 earthquake of 2000 and the subsequent discovery of a paleoseismic dislocation in the region which is still poorly known. New data were obtained through field surveys, electrical resistivity surveys, and analysis of previously unused materials from regional deep seismic profiles. These data were used to analyze tectonics, geological structure and morphostructural features of the area in relation to seismicity. The results indicate that the areas with the highest seismic potential are the Kingash and Kiyai-Okler faults branching off from the Iya-Kan fault, whose northwestern termination extends into the suburbs of Krasnoyarsk. The Kingash and Kiyai­Okler faults are well­defined and control the northeastern margin of the Meso­Cenozoic Sayan­Partizansk basin. The study in linear dislocation zones of these faults focused on seismogeological field reconnaissance and geophysical survey. Analysis of the obtained results and geological­geophysical data from published literature suggests that the Mana trough serves as a natural northwest-trending boundary for the seismogenic structures on the northeastern slope of the Eastern Sayan. The study demonstrates that the Main Sayan and Eastern Sayan faults do not pose a significant seismic hazard to Krasnoyarsk. The practical significance of the research results lies in refining the structure of earthquake source zones southeast of Krasnoyarsk and resolving contradictions in regional seismicity assessments on General Seismic Zoning (GSZ) maps for recent decades. The GSZ maps may show the Kingash and Kiyai­Okler faults as a single earthquake source zone confined to the Iya­Kan fault system. The potential maximum magnitude of this source zone is estimated at Mₘₐₓ=7.5 along extension. The source­related maximum possible intensity in Krasnoyarsk may reach 7.3 points on the MSK-64 scale.

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