Abstract
—The MW = 6.7, ML = 6.9 Khuvsgul (Khubsugul, Khövsgöl) earthquake occurred on January 12, 2021 in the Northern Mongolia close to the border of Russia. The earthquake caused ground shaking which reached intensity IX at the epicenter and was perceptible in the cities and villages of the Eastern and Western Siberia. The earthquake occurred in the region of the same-name fault and caused intense aftershock process on a segment between two fault’s bends. The fault segment encompassed by the aftershocks goes from the lake to the northwest. Seismic activation has involved a segment of the boundary of the ancient Tuva–Mongolian microcontinent hosting the parallel Khuvsugul and Darkhat rift depressions and the Busingol rift depression consisting of three linearly elongated troughs. Until the present, the region of the Busingol depression was distinguished by high seismicity, whereas the regions of the Darkhat and Khuvsgul depressions were characterized by moderate and low seismicity, respectively. The earthquake of 2021 is the largest earthquake that occurred on the Khuvsgul fault over the entire history. In less than two months, the level of the frequency–magnitude graph for the aftershocks has exceeded the level of the annual frequency–magnitude graph of the earthquakes for the Altai–Sayan mountain region. The aftershock density is nonuniformly distributed along the fault; the structure of the distribution is correlated to the unilateral block structure of the Earth’s crust east of the activated fault segment. The seismic potential of the Khuvsgul fault was estimated at Mmax = 7–7.5, and this earthquake, as suggested by the geological data, is not the maximum possible event. Given that seismic activation after the 1991 Busingol earthquake has not yet ceased, we have two strong activations in the Tuva–Mongolian block which can significantly affect evolution of its seismicity.
Highlights
INTRODUCTIONThis earthquake was followed by the intense pulsing aftershock process that has been going on for almost three decades (Emanov et al, 2005; 2006)
The ML = 6.9 Khuvsgul earthquake of January 12, 2021 occurred on the eastern boundary of the Tuva– Mongolian block and caused an intense aftershock process
The minimum residual was obtained with a source depth of the main shock at 8 km
Summary
This earthquake was followed by the intense pulsing aftershock process that has been going on for almost three decades (Emanov et al, 2005; 2006). Within the Khuvsgul depression, rare earthquakes with magnitude 5 were observed in the northern and southern parts, whereas the central part of the depression and, the epicentral zone of the 2021 earthquake were seismically not active. In (Kochetkov et al, 1993) it was concluded that in the region of the Khuvsgul fault extended along the western wall of the depression of the same name, the process of energy accumulation takes place, and the occurrence of the large earthquakes along this fault is probable. The Khuvsgul earthquake was perceived over a very large area (Fig. 10) spanning the territory of North Mongolia and several objects of the Russian Federa-
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