New aspects of tectonic stress inversion with reference to the TENSOR program

Abstract: Analysis of tectonic stress from the inversion of fault kinematic and earthquake focal mechanism data is routinely done using a wide variety of direct inversion, iterative and grid search methods. This paper discusses important aspects and new developments of the stress inversion methodology asthe critical evaluation and interpretation of the results. The problems of data selection and separation into subsets, choice of optimization function, and the use of non-fault structural elements in stress inversion (tension, shear and compression fractures) are examined. The classical Right Dihedron method is developed in order to estimate he stress ratio R, widen its applicability o compression and tension fractures, and provide a compatibility test for data selection and separation. A new Rotational Optimization procedure for interactive kinematic data separation of fault-slip and focal mechanism data and progressive stress tensor optimization is presented. The quality assessment procedure defined for the World Stress Map project is extended in order to take into account he diversity of orientations of structural data used in the inversion. The range of stress regimes is expressed by a stress regime index R', useful for regional comparisons and mapping. All these aspects have been implemented in a computer program TENSOR, which is introduced briefly. The procedures for determination