THE STYLE OF RECENT FAULTING IN THE VICINITY OF ULAANBAATAR (MONGOLIA)
K. ZH. SEMINSKY1, S. DEMBEREL2, A. A. BOBROV3, D. MUNGUNSUREN2, S. A. BORNYAKOV1, E. H. TURUTANOV1
1Irkutsk Scientific Center SB RAS, 664033, Irkutsk, Lermontova str., 134, Russia
seminsky@crust.irk.ru
2Institute of Astronomy and Geophysics MAS, 210351, Ulaanbaatar, Bayanzurh duureg, Maahuur tolgoi, 5-r horoo, SHUA-iyin 7-r bair, Mongolia
demberel@iag.ac.mn
3Institute of the Earth’s Crust SB RAS, 664033, Irkutsk, Lermontova str., 128, Russia
alexbob@crust.irk.ru
Keywords: разлом, сейсмическая зона, поле напряжений, землетрясение, радон, fault, seismic zone, stress field, earthquake, radon
Abstract
The faulted structure of the crust, one of the components of the Earth’s geographical environment, has been studied in the vicinity of Ulaanbaatar, Mongolia. The study resulted in defining the positions of fault zones and nature of their activity at the recent stage of tectogenesis. The field of epicenters of earthquake events occurred in the area in the period from 2000 to 2014 was analyzed, along with the soil radon activity field forming near the faults distinctly featured in the relief. It is established that seismic activity and radon activity are closely related. Based on this conclusion, a network of 13 active fault zones was discriminated in the vicinity of Ulaanbaatar. They are divided into four systems that have generally inherited the neotectonic faults network, however, they differ in details of the inheritance. The NW and SE-trending fault zones develop along to the youngest faults, while the latitudinal and meridional zones are generally located across such faults. The fault zones of the orthogonal network are markedly distinguished by chains of maximums in the field of earthquake epicenters. This suggest strike-slip faulting in the conjugated planes of shear stresses. Reconstructions for the study area show the recent field of shear stresses with the SW-NE oriented compression axis and the SE-NW-oriented extension axis. This field is a remote result of the Indo-Asian collision and typical of the regions located southwest of Ulaanbaatar. In this paper, the faulting style is characterized as a principal factor that must be taken into account in the assessment of seismic hazard facing the capital of Mongolia which population is over a third of the country’s total population.
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