Using in situ-produced ¹⁰Be to quantify active tectonics in the Gurvan Bogd mountain range (Gobi-Altay, Mongolia)

This paper presents an updated synthesis of morphotectonic studies that quantify active tectonics along the Gurvan Bogd mountain range in the Mongolian Gobi-Altay, the site of one of the strongest historic intracontinental earthquakes (Mw 8.1) in 1957. Our goal was to determine the slip rate along the constituent fault segments and to estimate the return period of such large events. Along each segment, cumulative offsets were estimated from topographic surveys, and the ages of the offset markers were determined using cosmic-ray exposure dating. In this review, we reevaluate ¹⁰Be data reported in previous publications using a chi-square inversion analysis of depth profiles and an updated scaling model for spatial production rate variations. We also discuss sampling strategies for dating alluvial fans in arid settings. This study confirms the low horizontal and vertical slip rates within the massifs of the Gurvan Bogd mountain range for the Late Pleistocene-Holocene period, suggests that episodes of aggradation occurred near the times of major glacial-interglacial terminations (at ca. 15-20 ka and ca. 100-130 ka), and provides evidence for another much earlier aggradational episode, occurring before 400 ka. The Bogd fault has a maximum horizontal left-lateral slip rate of ̃1.5 mm/yr, while reverse fault segments along the Gurvan Bogd fault system have vertical slip rates between 0.1 and 0.2 mm/yr. Characteristic dislocations observed along the Bogd fault suggest return periods of earthquakes similar to 1957 between 3000 and 4000 yr.