THE BELTIRSKOE (ML=6.4) AND KURAISKOE (ML=5.7) EARTHQUAKES IN 2025 AS A RESULT OF THE INFLUENCE OF THE 2003 CHUI EARTHQUAKE ON THE CHAGAN-UZUN BLOCK (GORNY ALTAI)
Emanov A.F.¹, Emanov A.A.¹,², Gladyshev E.A.¹, Fateev A.V.¹,², Novikov I.S.³, Shevkunova E.V.¹, Polyansky P.O.¹, Arapov V.V.¹
1 - Altai-Sayan Branch, Federal Research Center "Unified Geophysical Service of the Russian Academy of Sciences", Novosibirsk,Russia;
2 - Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia;
3 - Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia.
Keywords: seismology, geophysics, earthquakes, seismic hazard, tectonic faults, Gorny Altai, Chagan-Uzun block
Abstract
This paper examines the geological setting of the two strongest earthquakes recorded in the Altai-Sayan mountainous region in 2025: the Beltirskoe earthquake (ML=6.4) and the Kuraiskoe earthquake (ML=5.7), which occurred on opposite margins of the Chagan-Uzun block. Data on the aftershock sequences of these earthquakes are presented. The analysis demonstrates that these earthquakes occurred in the vicinity of, yet outside, the source region of the 2003 Chuia earthquake. The 2025 events were studied with reference to available data on the aftershock activity of the Chuia earthquake. It is shown that the Chuia earthquake is associated with the shear zone of the eponymous fault and encompasses a linear area along one of the margins of the Chagan-Uzun block. During the main shock, the block itself was incorporated into the source region in the form of weak earthquakes occurring beneath it at depths of 10–20 km (a seismically active layer adjacent to the Chuia earthquake source zone). The focal mechanisms of the Beltirskoe and Kuraiskoe earthquakes are thrust-type, whereas the mechanisms of all strong aftershocks of the Chuia earthquake are strike-slip. Both 2025 earthquakes generated aftershock sequences of low intensity. The hypocenters of the main events and the majority of aftershocks are located at shallow depths, with a maximum concentration at approximately 3–5 km.
The 2025 earthquakes represent a continuation of seismic activity in the Altai region within the near-field zone of the Chuia earthquake, reflecting a delayed temporal response of crustal blocks that experienced alterations in their stress state following the impact of a major seismic event.
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