Preprints
https://doi.org/10.5194/se-2021-91
https://doi.org/10.5194/se-2021-91

  30 Aug 2021

30 Aug 2021

Review status: this preprint is currently under review for the journal SE.

Tectonic Geomorphology and Paleoseismology of the Sharkhai fault: a new source of seismic hazard for Ulaanbaatar (Mongolia)

Abeer Al-Ashkar1, Antoine Schlupp1, Matthieu Ferry2, and Ulziibat Munkhuu3 Abeer Al-Ashkar et al.
  • 1Institut Terre et Environnement de Strasbourg, UMR 7063, Université de Strasbourg/EOST, CNRS ; 5 rue René Descartes, Strasbourg, 67084, France
  • 2Géosciences Montpellier, Université de Montpellier - CNRS, Montpellier, France
  • 3Institute of Astronomy and Geophysics, Mongolian Academy of Sciences, Ulaanbaatar, Mongolia

Abstract. We present new constraints from tectonic geomorphology and paleoseismology along the newly discovered Sharkhai fault near the capital city of Mongolia. Detailed observations from high resolution Pleiades satellite images and field investigations allowed us to map the fault in detail, describe its geometry and segmentation, characterize its kinematics, and document its recent activity and seismic behavior (cumulative displacements and paleoseismicity). The Sharkhai fault displays a surface length of ~40 km with a slightly arcuate geometry, and a strike ranging from N42° E to N72° E. It affects numerous drainages that show left-lateral cumulative displacements reaching 57 m. Paleoseismic investigations document the faulting and deposition record for the last ~3000 yr and reveal that the penultimate earthquake (PE) occurred between 1515 ± 90 BC and 945 ± 110 BC and the most recent event (MRE) occurred after 860 ± 85 AD. The resulting time interval of 2080 ± 470 years is the first constraint on the Sharkhai fault for large earthquakes. On the basis of our mapping of the surface rupture and the resulting segmentation analysis, we propose two possible scenarios for large earthquakes with likely magnitudes between 6.4 ± 0.2 and 7.1 ± 0.2. Furthermore, we apply scaling laws to infer coseismic slip values and derive preliminary estimates of long-term slip rates between 0.2 ± 0.2 and 1.0 ± 0.5 mm/y. Finally, we propose that these original observations and results from a newly discovered fault should be taken into account for the seismic hazard assessment for the city of Ulaanbaatar and help build a comprehensive model of active faults in that region.

Abeer Al-Ashkar et al.

Status: open (until 29 Oct 2021)

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Abeer Al-Ashkar et al.

Abeer Al-Ashkar et al.

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Short summary
We present tectonic geomorphology and paleoseismology along the newly discovered Sharkhai fault near the capital city of Mongolia. The fault length is of ~40 km, the last earthquake occurred between 1515 ± 90 BC and 945 ± 110 BC and the previous occurred after 860 ± 85 AD. Associated magnitudes are between 6.4 ± 0.2 and 7.1 ± 0.2 and long-term slip rates between 0.2 ± 0.2 and 1.0 ± 0.5 mm/y. The Sharkhai fault should be taken into account for the seismic hazard assessment for Ulaanbaatar.