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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]

Abstract: The structure of the Earth’s crust at the junction of the Siberian craton and Sayan–Baikal Fold Belt was studied along the Bayandai Village–Cape Krestovskii profile (85 km long) by a set of geological and geophysical methods: structural survey, interpretation of long-distance photographs, emanation survey, electrical prospecting with self-potential (SP) and direct-current (DC) resistivity profiling, magnetotelluric sounding, magnetic survey, and hydrogeochemical sampling of water objects. Interpretation of the data refined the main features of the tectonic structure of western Cisbaikalia and revealed the disruption pattern and hierarchic zone–block structure of the Earth’s crust. The Obruchev fault system (≈50 km wide), which is the northwestern shoulder of the Baikal Rift, is the main interblock zone of the studied region. It consists of the Morskoi, Primorskii, and Prikhrebtovyi interblock zones, traced from depths of tens of kilometers and widening near the surface owing to superior structures. The studies gave an insight into the regularities in the occurrence of interblock zones and the criteria for their identification in different geologic-geophysical fields. An efficient complex of methods for mapping the Earth’s crust zone–block structure is proposed. [Copyright &y& Elsevier]

Abstract: We report results of transect radon surveys on twenty six large and small faults of different geometries in the western Baikal and southern Angara (southern Siberian craton) areas. The studied faults show up in the radon field as broad zones of high radon activity concentration, with their widths 1.4 times the widths of faulting-related deformation zones. Other things being equal, radon emanation depends on the size and slip geometry of faults and on their activity in the Cenozoic. Relative radon activity is higher in rift faults than in cratonic ones, in normal relative to strike-slip faults, and in larger and more active faults, the latter factor being the basic geodynamic control of radon emanation. [Copyright &y& Elsevier]