Método β-stress para corregir la orientación de los ejes principales del esfuerzo determinados a partir del análisis poblacional de sistemas incompletos de fallas con simetría ortorrómbica.

Abstract

The techniques of fault-slip stress inversion can be used on faults that follow the slip model (with four fault sets arranged in a system with orthorhombic symmetry) to determine the position and magnitude of the principal stress axes. In incomplete fault systems (less than four sets) the calculated stress axes are commonly inclined. It is shown here that, in complete fault systems, variations in fault dip and striae pitch do not modify the trend or the plunge of the here-called invariant stress axis (σ1 for reverse faults and σ3 for normal faults). This feature allowed us to propose a new empirical technique, the β-stress method, to correct the position of the invariant stress axes in incomplete fault systems. One of the assumptions of the method is that one of the principal stress axis is vertical. The β-stress method yields the horizontal deviation angle, β, between the trend of an inclined invariant axis determined from an incomplete fault system, and the theoretical, correct attitude of this axis, which would have been measured if the four sets of the complete system were available at the studied outcrop. The method has been successfully applied to correct the orientation of the principal stress axes obtained after stress inversion of Miocene and Pliocene-Quaternary faults located in the Gulf of Cádiz.