Active intraplate deformation as a far-field effect of the India-Eurasia convergence has led to four Mw∼8 earthquakes in western and southern Mongolia in the past century. Palaeoseismological and morphotectonic studies have shown that these earthquakes are characteristic events along transpressive fault systems with cumulative offsets. The tectonically active Gobi Altai and Hangay mountains are separated by the seismically quiescent Valley of Gobi Lakes, which consists of major perennial rivers draining into endorheic lakes. Despite the scarcity of recorded earthquakes, Quaternary deposits in the Valley of Gobi Lakes are crosscut by multiple fault scarps with significant, landscape-altering displacements. To assess past earthquakes and the potential seismic hazard of this area, we apply remote sensing, tectono-morphometric techniques and cosmogenic nuclide dating to estimate the amount of deformation the faults in the Valley of Gobi Lakes are accommodating, and to determine the effect of these faults on local landscape evolution. The Tuyn Gol (gol = Mongolian for river) is crosscut by four E-W to NE-SW trending fault scarps that display variable fault kinematics due to scarp orientation differences relative to a stable NE-SW principle stress direction. Mapping of the >40–90 km long Valley of Gobi Lake faults shows that they can accommodate M ∼ 7 earthquakes. Offset measurements of the Tuyn Gol deposits allow Middle Pleistocene to modern vertical slip rate estimates and M ∼ 7 earthquake recurrence intervals of 0.012 ± 0.007–0.13 ± 0.07 mm/yr and 5.24 ± 2.61–81.57 ± 46.05 kyr, respectively. Cumulative vertical displacement amounts to 0.27 ± 0.08 mm/yr, which is similar to that of major tectonic structures such as the Bogd fault in the Gobi Altai. This implies that the total active deformation accommodated by southern Mongolian faults may be larger than previously expected and distributed across more faults between the Hangay and the (Gobi) Altai mountain ranges. Geomorphological observations and surface exposure dating indicate that the Tuyn Gol drainage system developed over four to five 100 kyr climate cycles, during which active deformation played an important role in drainage reorganization. Our results demonstrate the dominant role of tectonics on local landscape dynamics, indicating the importance of studying regional geomorphology to adequately estimate the earthquake potential of faults that were considered inactive.

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This study investigates the late Quaternary development of the sedimentary system of Orog Nuur Basin in southern Mongolia. Geomorphological archives (lacustrine sediments and beach ridges, alluvial fans, aeolian deposits, peat) recorded palaeoenvironmental change from marine isotope stage (MIS) 7 to the late Holocene. Synthesizing the variety of archives allows a better understanding of geomorphological interactions in arid regions and palaeoenvironmental implications for the area. By performing palaeoshoreline mapping and dating, we identified eight palaeolake levels resulting in a refined lake level history of Orog Nuur. The highest reliably dated shoreline is about 56 m higher than today's lake level and provides evidence for a late MIS 5 lake level between 100 and 75 thousand years (ka). Reconstructions yield a minimum volume estimate of 24.5 km3, delineating a lake that is 153 times larger than that of today (0.16 km3). Massive lake extensions occurred also during MIS 3 and the Holocene. The geomorphological investigation reveals late MIS 5 and MIS 3 lake expansions were of similar magnitude. The palaeoenvironmental reconstruction from early Holocene archives indicates that lake expansion was caused by an increase in precipitation and meltwater inflow from the surrounding mountain systems. Afterwards, lake levels declined with some intermittent highstands during the mid‐Holocene (7–5 ka), indicating a general trend towards a lower water inflow throughout the Holocene. Palynological reconstructions of the alpine vegetation development reveal that mid‐Holocene highstands (c. 6.5 ka and 5.5 ka) were fed by higher precipitation in the nearby Gurvan Bogd range. Mountain silts, basin silty sands, and Holocene dune deposits provide further evidence for paleoenvironmental change. As controlling factors of the sedimentary system, we identified changes in effective moisture, higher precipitation values and the contribution of meltwater. Orog Nuur Basin archives are valuable for landscape and palaeoenvironmental reconstructions and for comparisons in supraregional reconstruction approaches.

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<p>The tectonically active northern margin of the Gobi Altai in southern Mongolia is best known for the 1957 Mw 8.1 Bogd earthquake. Cumulative offsets along the Bogd fault indicate that the area was subject to repeated earthquakes in the past. North of the Bogd fault, the Valley of Lakes characterises a seismically quiescent zone between the Gobi Altai and the central Mongolian Hangay dome, with little to no instrumentally recorded earthquakes. However, Quaternary alluvial fans of rivers that drain toward the endorheic lakes in this basin are crosscut by multiple fault scarps with displacements up to 15 m. Additionally, river channel morphology is significantly altered by tectonic lineaments indicating that, despite the lack of recorded seismicity, this area may indeed have been seismically active in the recent past. By applying remote sensing techniques, UAV photogrammetry, and morphometric studies, we aim to understand i) the effect these faults had on the landscape evolution of the Valley of Lakes, ii) their relationship to deformation along the Bogd fault and iii) whether these faults accommodate a significant amount of strain related to the India-Eurasia collision.</p><p>The lack of available material for dating requires palaeoseismological studies to make use of morphotectonic observations as an alternative, relative dating method. At the Bogd fault, such studies were combined with sparsely available cosmogenic nuclide age data to determine that vertical slip rates vary between 0.1 and 1 mm/yr on individual faults and at the scale of the entire mountain front, respectively. In the Valley of Lakes, a total lack of age data complicates the extrapolation of slip rates, however scarp degradation indicates that slip rates are likely lower than at the Bogd fault. Fluvial terraces of the Tuyn Gol river are crosscut by at least three major fault scarps, which contribute to valley width variations of the river from ±3500 m to ±20 m at the current fan apex, and which are reflected in steepness index variations along minor drainages. Additionally, a large paleochannel suggests that major drainage reorganisation events took place in Quaternary times, either reflecting periods of high tectonic activity or as a result of significant climate variations. The transtensional nature of some faults in the Valley of Lakes is unique; however fault mechanisms in the area are generally in line with the active deformation in the Gobi Altai. Our results stress the earthquake potential of regions with low instrumental seismicity and demonstrate that deformation in the Gobi Altai may reach further north than previously expected.</p>