Reinterpretation of the active faulting in central Mongolia

Abstract

We present remote-sensing and fi eld observations of an ~350-km-long east-west left-lateral strike-slip fault (the South Hangay fault) in the Hangay Mountains of central Mongolia, an area previously believed to be deforming solely by slip on scattered, and randomly oriented, normal faults. The known dip-slip faults are shown to be short segments introduced at bends in the much longer strike-slip fault. Our observations show that the active faulting in the Hangay Mountains is consistent with the regional strain fi eld of Mongolia and does not require, as suggested in other studies, that the faults result from stresses introduced by the locally elevated topography. Our observations help to defi ne the active tectonics of this important part of the India-Eurasia collision. The South Hangay strike-slip fault is a potential source of large-magnitude earthquakes and constitutes a previously unrecognized hazard in this part of Mongolia.

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

“…Many of the active faults have slip vectors consistent with the regional east-west left-lateral shearing measured by GPS (Calais et al 2003). Walker et al (2007Walker et al ( , 2008 identified a number of east-west left-lateral fault systems, all showing evidence of activity in the late Quaternary, within the western and southern parts of the Hangay Mountains (Fig. 1).…”

“…However, there is uncertainty as to whether the slip vectors on the normal faults are consistent with the regional strain field or whether they respond purely to the local extensional stresses associated with doming (e.g. Baljinnyam et al 1993;Cunningham 2001;Walker et al 2007Walker et al , 2008. Determining the slip vectors of the normal faults, and hence determining whether they are compatible with the regional strain field, will help to distinguish between the differing scenarios.…”

“…The Egiin Davaa fault is one of several normal faults within the Hangay Mountains (e.g. Baljinnyam et al 1993;Cunningham 2001;Walker et al 2007Walker et al , 2008. It is expressed as a scarp in late Quaternary surfaces with a typical height of 4.5 m. The sharp geomorphology and continuity of displacement across and along the fault has led some researchers to the interpretion that it formed in a single earthquake rupture potentially related to an historical event recorded in the sixteenth century (e.g.…”

Nd isotopic compositions of the Tethyan Himalayan Sequence in southeastern Tibet

“…The similarity in the Nd isotope values between the Triassic strata in the THS on the northern Indian margin and the Tibetan terranes, along with early work indicating that the Triassic sediments in southeast Tibet were transported from a northern source, supports the early proposal that the Lhasa terrane and the Indian craton were both parts of the Gondwana; they were separated in the early Jurassic during the opening of the Neo-Tethys [3,15,16] . This geologic link suggests that Nd isotopic composition alone cannot be used as the sole criterion to differentiate Tibetan terranes from the Indian lithologic units [33,34] .…”

Investigation of Lithospheric Structure in Mongolia: Insights From Insar Observations and Modelling

“…They are mainly concentrated on four major fault systems, which extend for several hundred kilometers. These strike-slip faults are potential fragile zones to come about large-magnitude earthquakes (Walker et al, 2007). The Mw 8.1 December 4th 1957 Gobi-Altai earthquake happened on the Bogd fault, it is an east-west trending leftlateral strike-slip fault (Kurushin et al, 1997).…”