A stress inversion procedure for polyphase calcite twin and fault slip data sets

In rocks that are polydeformed an approach which separates faults prior to stress inversion is more appropriate. The traditional stress inversion appr oach involving the concept of the best-Jit stress tensor, e.g. a tensor whi ch minimises the misfit between calculated and measured fault-striae data, often risks computing artificial stress tensors that are some form of avera ge of mixed sets of real stress tensors. A new approach is proposed in whic h fault data are pre-processed to group the faults on the basis of their re sponse to all possible orientations and magnitudes of applied stress. A com puter method is described which utilises cluster analysis based on the righ t-dihedra method to divide dynamically-mixed fault populations to monophase subsets. This division is based on the ranked similarity coefficients of e ach fault pair from the raw data set. The data clusters form dynamically-ho mogeneous subsets, which are used for the composite right-dihedra solution. This solution is re-computed for the reduced stress tensor defined by the orientation of principal stress axes and the ratio of their magnitudes. (C) 1999 Elsevier Science Ltd. All rights reserved.