The Egiin Davaa prehistoric rupture, central Mongolia: a large magnitude normal faulting earthquake on a reactivated fault with little cumulative slip located in a slowly deforming intraplate setting

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 semicontinuous 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.

Great earthquakes in low strain rate continental interiors: An example from SE Kazakhstan

“…The 1897 M w 8.1 Assam earthquake, India, is also thought to have involved slip of 11–25 m of slip on a fault 110 km in length [ Bilham and England , ]. Well‐constrained prehistoric examples also exist, for example, the ∼4 ka Egiin Davaa paleo‐earthquake rupture in Mongolia, which involved almost uniform slip of ∼8 m along an 80 km length [ Walker et al , ]. These examples are all from intraplate regions, where the seismogenic thickness may be larger than typical, and the large slip at Lepsy may be related to the structural immaturity of the fault, which appears to be a major factor in controlling the magnitude of slip in an earthquake, with “immature” faults tending to fail in shorter though more energetic ruptures [ Manighetti et al , ].…”

The earthquake deformation cycle

“…While further painstaking work scouring satellite imagery and checking sites in the field can and will improve our knowledge of active faults (e.g. Walker et al, 2015), many faults will only be discovered when they fail in earthquakes. For example, the faults that caused the M6.5…”

Controls on Early‐Rift Geometry: New Perspectives From the Bilila‐Mtakataka Fault, Malawi

“…In intact, isotropic rocks, normal border faults would strike perpendicular to the least principal stress and dip 60°. Frictionally weak and/or low cohesive strength caused by preexisting structures can, however, localize strain and provide surfaces for fault reactivation (e.g., Bellahsen et al, ; Walker et al, ; Worthington & Walsh, ), including structures that are not ideally oriented in the current stress field (e.g., Ebinger et al, ). Therefore, preexisting structures formed in both current and previous deformation phases can have a fundamental influence on rift geometry (e.g., Phillips et al, ; Whipp et al, ).…”