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Palaeoseismological studies were performed within the Yaloman graben (Gorny Altai). Five Quaternary sections with coseismic deformation structures (seismites) have been recognized in the lower course of the Malyi Yaloman River. Traces of ancient earthquakes are localized at two levels (Late Pleistocene–Holocene). The most likely mechanisms of the seismite formation are brittle failure, liquefaction, and fluidization. The types of coseismic deformations and their sizes suggest that the Yaloman graben was the locus of prehistoric earthquakes with M ≥ 5–7, although modern-day seismic activity consists of smaller-magnitude earthquakes. This should be taken into account in assessing the seismic hazards during construction of gas pipeline to China and tourism infrastructure facilities.

We study earthquake-induced soft-sediment deformation (seismites) in reference Quaternary sections of southeastern Altai. Sediments in the sections bear signature of liquefaction and fluidization and deformation is localized in thin (few centimeters to 0.5–1.0 m) continuously striking and frequently repeated layers sandwiched between undeformed sediments. The soft-sediment deformation records coseismic motion of different slip geometries. Seismic origin is also inferred for layers and lenses of coarse colluvium slid into the lake bottom from the slopes, which intrude plane-bedded silt and sand and vary in thickness from a few centimeters to one meter. The occurrence of seismic soft-sediment deformation at different stratigraphic levels of the Quaternary and in the Upper Pliocene Beken Formation confirms the high seismicity of southeastern Altai in Quaternary time.