Geophysical research: article

Аnnotation: The behavior critically stressed fractures existing in rock masses of the upper layers of the Earth’s crust is studied. Spatial orientations of these fractures are the main focus of the study, with azimuthal and dip angles providing a critical stress state of natural shear fractures at varying depth being particularly analyzed. Depths up to 3 km are analyzed. An analytical solution for the limits on azimuthal and dip angles of critically stressed fractures obtained for given depth and ratio between principal stresses is given in the paper. Usage of stereogram as a tool for studying the spatial orientations of critically stressed fractures is described. A series of stereograms providing an opportunity to analyze the main patterns in changes of fractured zones’ properties with depth are constructed. A relationship between azimuthal and dip angles of critically stressed fractures existing at different depths and effective internal friction coefficient of rock masses is established. The depths acting as boundary for domains of critically stressed fractures are found for different stress regimes. The maximum depth providing a possibility for any fracture to be critically stressed is determined for Reverse Fault stress regime. At the same time, the minimum depth for critically stressed fracture to emerge is determined for Normal Fault stress regime. It is shown that the domain of critically stressed fractures may be constructed on a stereogram characterizing a certain volume of fractured rock mass for the given components of stress tensor acting in this volume. If the hypothesis of one principal stress being directed in vertical direction is true, then it is enough to know depth of the studied object and ratio between horizontal stresses in the region in order to construct a stereogram. The obtained results may be used for preliminary analysis of fractured zones existing in rock masses.