Abstract
Abstract The prehistoric Egiin Davaa earthquake rupture is well-preserved in late Quaternary deposits within the Hangay Mountains of central Mongolia. The rupture is expressed by a semi-continuous 80 km-long topographic scarp. Geomorphological reconstructions reveal a relatively constant scarp height of 4–4.5 m and a NW-directed slip vector. Previous researchers have suggested that the scarp's exceptional geomorphological preservation indicates that it may correspond to an earthquake that occurred in the region c. 500 years ago. However, we constrain the last rupture to have been at least 4 ka ago from morphological dating and <7.4 ka ago based on radiocarbon dating from one of two palaeoseismic trenches. Our study shows that discrete earthquake ruptures, along with details such as the locations of partially infilled fissures, can be preserved for periods well in excess of 1000 years in the interior of Asia, providing an archive of fault movements that can be directly read from the Earth's surface over a timescale appropriate for the study of slowly deforming continental interiors. The Egiin Davaa rupture involved c. 8 m of slip which, along with the observations that it is largely unsegmented along its length and that the ratio of cumulative slip ( c. 250 m) to fault length ( c. 80 km) is small, suggests relatively recent reactivation of a pre-existing geological structure. Supplementary material: All scarp profiles are available at http://www.geolsoc.org.uk/SUP18871
Highlights
Along an ancient fault with,300 m of cumulative throw
We focus on the Egiin Davaa prehistoric normal faulting earthquake from central Mongolia (e.g. Khil’ko et al 1985; Baljinnyam et al 1993), which formed a semi-continuous rupture 80 km in length and for which we estimate a magnitude of 7.3–7.7
This study presents the results of 80 km of fault mapping, topographic profiling and the interpretations of two palaeoseismic sites along the Egiin Davaa normal fault within the Hangay Mountains of central Mongolia (Fig. 1)
Summary
Along an ancient fault with ,300 m of cumulative throw. A study of the Egiin Davaa rupture is important for understanding the potential for large destructive earthquakes on faults with little or no expression and for investigating the processes of fault initiation and reactivation. We focus on the Egiin Davaa prehistoric normal faulting earthquake from central Mongolia (e.g. Khil’ko et al 1985; Baljinnyam et al 1993), which formed a semi-continuous rupture 80 km in length and for which we estimate a magnitude of 7.3–7.7. We assess whether the Egiin Davaa fault scarp was likely to have been caused by a single earthquake and we provide estimates of its likely magnitude, age and slip direction.
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