Abstract
We have compiled and analyzed earthquake focal solutions for the territory of Mongolia and its surroundings in order to reveal a spatial variability of stress orientation and stress regimes of the crust. According to the stress inversion results, the SHmax is turning from W-E in the eastern Mongolia to SW-NE in the Gobi Altay and the central Mongolia, and then to S-N in the western part of the region. Comparison with data derived from GPS measurements shows that directions of the strain axes revealed by the geodetic and seismological observations are generally consistent. A contradiction is found for the Bolnai zone where results of GPS estimation indicate the predominance of extension (in the SE-NW direction), whereas earthquake data for the longer period of seismic observations reveal compression. Compression in this zone is mainly due to the Tsetserleg-Bolnai earthquakes contribution; however, a part of the recent data on focal mechanisms fits an extensional stress field with the NNW orientated extension axis. These data are in accordance with some published works which suggest a transtensive field from some structural geology studies in the eastern part of the Bolnai zone. The paper is supplemented with a list of M≥4.5 earthquake fault plane solutions and unpublished focal mechanisms for some M≤4.5 earthquakes of the northern Mongolia and the southern Baikal region.
Highlights
Data on stress regimes and strain rates for intracontinental domains are of particular interest for understanding intraplate seismicity
The first conclusion inferred from the map is that the focal solutions of earthquakes in the southern Mongolia are rather homogeneous, whereas in the northern part they are widely variable
The results show that SHmax is turning from the W-E direction in the eastern Mongolia to NE-SW in the Gobi Altay and the central Mongolia, and to S-N in the western part of the region (Fig. 5)
Summary
Data on stress regimes and strain rates for intracontinental domains are of particular interest for understanding intraplate seismicity. The eastern part of Mongolia, which is characterized by the moderate level of seismic activity and diffusive seismicity type, might be influenced by the Pacific subduction process [Barth, Wenzel, 2010; and others]. This part is assumed to belong to the Amurian block or plate, the existence of this plate is doubted by some researchers [De Mets et al, 1990; Calais et al, 2003; and others]. Local mantle anomalies, such as one under the Khangay dome, whose uplift is thought to be resulting from hot mantle upwelling [Windley, Allen, 1993; Priestley et al, 2006; and others] should not be excluded from consideration
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