Timing of formation of forebergs in the northeastern Gobi Altai, Mongolia: implications for estimating mountain uplift rates and earthquake recurrence intervals

Abstract

Bedrock and Quaternary alluvial fans in the forelands of the northern Gobi Altai have been faulted and warped by foreland-propagating thrust faults to form elongate hills known as forebergs. Forebergs near Bogd town, north of Arsta Bogd, and at Ih Hetsüü, north of Baga Bogd were mapped and their formation constrained using luminescence dating of lacustrine and fanglomerates sediments to give localized uplift rates of c. 0.05 m ka − 1 , and between c. 1.6 and 4.1 m ka − 1 , respectively. Comparisons between vertical surface rupture during the 1957 Gobi Altai earthquake with the age and amount of uplift of lacustrine sediments provide a tentative estimate of between 1288 ± 382 to 497 ± 120 years for the average recurrence interval of great earthquakes in the Baga Bogd region. These localized uplifts rates support the view that the Gobi Altai Mountains probably took between 50 and 25 million years to form and were, therefore, coeval with the uplift of the Himalayas and the Tibetan Plateau.