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
R. T. Walker, K. W. Wegmann, A. Bayasgalan, R. J. Carson, J. Elliott, M. Fox, E. Nissen, R. A. Sloan, J. M. Williams, E. Wright, 2017. "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", Seismicity, Fault Rupture and Earthquake Hazards in Slowly Deforming Regions, A. Landgraf, S. Kübler, E. Hintersberger, S. Stein
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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
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Palaeoseismic records and seismological data from continental interiors increasingly show that these areas of slow strain accumulation are more subject to seismic and associated natural hazards than previously thought. Moreover, some of our instincts developed for assessing hazards at plate boundaries might not apply here. Hence assessing hazards and drawing implications for the future is challenging, and how well it can be done heavily depends on the ability to assess the spatiotemporal distribution of past large earthquakes. This book explores some key issues in understanding hazards in slowly deforming areas. Examples include classic intraplate regions, such as Central and Northern Europe, Mongolia, Inner Mongolia, Australia, and North and South America, and regions of widely distributed strain, such as the Tien Shan Mountains in Central Asia. The papers in this volume are grouped into two sections. The first section deals with instrumental and historical earthquake data and associated hazard assessments. The second section covers methods from structural geology, palaeoseismology and tectonic geomorphology, and incorporates field evidence.