SHEAR ZONES AS A NEW-TYPE OF PALEOSTRESS INDICATOR

This paper proposes that shear zones act as palaeostress indicators in much the same way as brittle faults. Several hundred shear zones, fro m both the limbs of the Variscan Langland-Mumbles anticline (South Wal es), are treated using the graphical and numerical methods of fault sl ip analysis. Estimated palaeostress directions derived from shear zone s are characterized by greater scatter than where brittle faults are u sed as stress indicators. An important reason for this is the fact tha t on some shear zones the direction of maximum shear stress (slip line ation) is not perpendicular to the line of SIC intersection. As a cons equence, the use of slip lineations produces better solutions than cas es where the slip direction is inferred as a line perpendicular to the SIC intersection. The filtering of data to reduce the scatter in the results produces insignificant improvement and is considered unnecessa ry.