Earthquake Induced Landslides in Russian Altai: Absolute Dating Applying Tree-Ring and Radiocarbon Analysis

In order to properly understand the seismic potential of a region, and to assess the associated seismic hazard, extensive studies are necessary to take full advantage from the geological evidence of past earthquakes including seismically triggered landslides. As a period of instrumental observations is insignificant in comparison with the recurrence interval of strong earthquakes the historical data are being involved as well as paleoseismogeological investigations, which are focused on studying ground effects from past earthquakes preserved in the geologic and geomorphic environment. In this context absolute age determination of such ground effects, including seismically triggered landslides, is one of the key problems. By now radiocarbon method is the most exploitable and widely applicable dating technique in numerical age estimations of seismically induced landslides. In case of spreading the forest vegetation in seismically active areas tree-ring analysis can be used as an additional or alternative approach. It has a great potential due to utmost precision of dating. In this study we report new radiocarbon dates of previously unknown evidences of strong prehistoric earthquakes within the highest and most seismically active southeastern part of Russian Altai (SE Altai) during the last 4 ka. In addition to estimating the germination ages of trees growing on the bare surfaces of seismically-triggered landslides, utilizing dendrochronological analysis of wood penetrating injuries of trees (both dead and living ones) caused by seismically induced rock-falls allowed establishing the date of strong medieval earthquake—AD 1532. Obtained results argue for the high regional seismicity in the second half of the Holocene and clarify the chronology of seismic events within the SE Altai. The specified recurrence interval of strong earthquakes is about 400 years during the last 4000 years.