Abstract
The primary objective is the analysis of the elastic stress fields and prediction of incipient secondary faulting associated with the interaction of two overlapping, en echelon faults with a sense of stepover opposite to the sense of shear on the faults. Attention is focuses on the role of variable fault spacing and overlap for constant far-field compressive principal stresses. The linear elastic, isotropic, plane strain, finite element analyses are obtained. The basic modeling approach is validated by the excellent agreement between the numerical and analytical solutions for a single fault with a uniform coefficient of friction. The effect of fault overlap on the stress field is different from that of fault spacing. For fixed spacing, a decrease of fault overlap increases all stress components in the overlap region, but (Yxx and the maximum principal stress (cyl) exhibit the greatest absolute changes. The normal and shear stresses on the overlapping segments of the faults also are increased as overlap decreases. For a fixed overlap, a decrease in fault spacing primarily produces a significant increase of the (Yxx but small decreases for (Yyy and cyxy components within the overlap region. The enhancement of cyxx dominates the increase of cyl and the change of the principal stress direction in the overlap region. In the overlap region, CT] increases much more than (73, which reflects the dominance of the change of the cyxx. Incipient secondary faulting in the overlap region is analyzed by combining the elastic stress field with the Mohr-Coulomb failure criterion. Zones of potential faulting are identified by calculating a shear-failure parameter, F, which represents the effective cohesion that the rock needs in order to prevent shear failure for the specified far-field stress. Contrary to initial expectations, the overlap region on average is not a region of large F-value; hence, extensive incipient secondary faulting in the overlap region is not predicted, at least not for the far-field stresses used in these analyses. For small overlap and spacing, however, secondary faulting is predicted to be localized within the overlap region near the fault tips.
Leem, Junghun (1995). Finite element analysis of elastic interaction of two en echelon overlapping faults. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1995 -THESIS -L445.