Fundamental additions and modifications to the classical stress/strain ellipsoid

Abstract

Application of the stress/strain ellipsoid as defined by Harding (1974) to fractures observed in the Australian continent proved to be unsatisfactory. In a new modified ellipsoid, thrust faults are postulated to be bounded by both the synthetic fault, and an additional sub-parallel 'K'-lineament which has an opposite sense of displacement to the synthetic. Thrusting occurs when these bounding faults are convergent, and where they are divergent there is extensional faulting. With this modification, a single E-W right-lateral stress/strain ellipsoid can account for the orientation of more than 90 per cent of the main fault systems in the Australian continent. Many other faults can also be accounted for when Tertiary E-W compression is superimposed on older fractures. Detailed fault analysis using the classical ellipsoid in producing Cooper/Eromanga Basin fields reveals en echelon sub-fractures as predicted by theory. However, some have opposite strike movements which are explained by the 'K'-lineament.