Abstract
The orientation of fractures with transpressional and transtensional wrenches in pre-existing faults has not been quantitatively determined. Based on Coulomb failure criterion and Byerlee’s frictional sliding criterion, this paper has indicated quantitative geometric relationships between the pre-existing fault and the local induced principal stress axes caused by the rejuvenation of the pre-existing fault. For a hidden pre-existing fault with some cohesion, the angles between the local induced principal stress axes and the pre-existing fault quantitatively vary with the applied stress and the cohesion coefficient, the ratio of the thickness of the cover layer to the thickness of the whole wrench body, whether transpressional or transtensional wrenches occur. For a surface pre-existing fault with zero cohesion, the angles between the pre-existing fault and the local induced principal stress axes are related to the rock inner frictional angle regardless of both the applied stress and the cohesion coefficient where transpressional wrenches occur, and the local induced maximum principal stress axis is identical with the applied maximum principal stress axis where transtensional wrenches occur. Therefore, the geometric relationships between the pre-existing faults and their related fractures are defined, because the local induced principal stress axes determine the directions of the related fractures. The results can be applied to pre-existing weak fabrics. They can help to understand and analyze wrench structures in outcrops or subsurface areas. They are of significance in petroleum exploration.
Highlights
Wrench zones and their related structures were common both in outcrops and in oil-bearing areas [1]-[11]
For a surface pre-existing fault with zero cohesion, the angles between the pre-existing fault and the local induced principal stress axes are related to the rock inner frictional angle regardless of both the applied stress and the cohesion coefficient where transpressional wrenches occur, and the local induced maximum principal stress axis is identical with the applied maximum principal stress axis where transtensional wrenches occur
In a transtensional wrench with some cohesion coefficient, the geometric relationships between the wrench related fractures and the pre-existing weak fabrics are determined by the applied stresses like the Equation (9), and they will not be discussed in detail in this paper
Summary
Wrench zones and their related structures were common both in outcrops and in oil-bearing areas [1]-[11]. They are of significance in exploration of oil and gas [12] [13] [14] [15]. There are certain geometric relationships between the fractures and the principal displacement zone in a pure strike-slip [21] [24], there is little analytical discussion on the geometric relationship between the fractures and the pre-existing faults with transtensional and transpressional wrenches [25]. The results will help to understand wrench related structures both in outcrops and in basins They can help to the exploration of mineral resources, such as iron, oil and gas. The results will help to analyze structures in a normal fault or a reverse fault
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