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The relationship between radon and the tectonic activity of faults for two geodynamically active regions of Central Mongolia is shown with account for the influence of individual characteristics of the radon field. As a whole, the radon activity of the faults increases with an increasing contribution of extension to the dynamic environment of their formation, with increasing seismic activity, and near concentrated faults of the late stages of evolution in comparison with the wide zones of fractures at the early stages of the formation of the internal structure. The studied patterns should provide an increase in the efficiency of application of radon surveys in investigation of the seismic hazard of faults in the Earth's crust. [ABSTRACT FROM AUTHOR]

Examples of two geodynamically active regions in Central Mongolia are used to demonstrate the radon and tectonic activities of faults and find out how their individual parameters affect the radon field. In general, the radon activity of faults increases with the higher contribution of extension in dynamic faulting conditions, with stronger seismic activity, and also in concentrated disjunctive structures at their late evolution stages compared to wide rupture zones at the initial formation stages of their internal structure. Nonuniform structure is an intrinsic property of near-fault radon anomalies, which is defined primarily by nonuniform disruptions of the substrate in the fault zone by ruptures and by spatial variations in the displacement amplitude. Taking the established regularities into account will facilitate a higher efficiency of emanation surveys in studies of seismic hazard associated with crustal faults. [ABSTRACT FROM AUTHOR]

The data of the profile gas emanation survey conducted on three spatial scales in separate regions of the Mongolia-Baikal seismic belt are generalized to establish the regularities of the spatially heterogeneous distribution of soil radon activity above the active faults in the Earth's crust. It is shown that the shapes, sizes, and contrast of the near-fault radon anomalies are complicated by erosion and weathering; however, the critical role in their formation is played by the structural-geological controls, which determine the internal structure and recent activity of the fault zones. As a consequence, the cross-fault shape of the studied radon anomalies is vitally controlled by four structural situations, which correspond to the combinations of the structural type of the fault (localized/distributed) and the presence/absence of the fine filler material in the zone controlled by the fault. The cross-fault dimension of the emanation anomaly is commensurate or slightly larger than the width of the fault zone comprising all the fractures and joints associated with the formation of the main fault, which, due to the low permeability of the tectonites, is in most cases marked by the lowest concentration of soil radon. The contrast of the emanation anomalies, which we suggest to estimate in terms of a relative parameter K, gravitates to certain levels of this parameter. This provides the basis for distinguishing five groups of the fault zones with low ( K ≤ 2), moderate (2 < K ≤ 3), increased (3 < K ≤ 5), high (5 < K ≤ 10), and ultrahigh ( K > 10) radon activity. The previous studies show that for increasing the efficiency of the emanation survey in the fault zones, it is advisable to set up long profiles, reduce the measurement step in the vicinities of the main faults, specify the threshold of identifying the anomalies at the arithmetic mean level over the profile, and use the relative parameter K for comparing and estimating the faults in terms of the intensity of their radon activity. [ABSTRACT FROM AUTHOR]