The Australian Stress Map

Abstract

Knowledge of the in situ stress field of the Australian continent has increased greatly since compilation of the World Stress Map in 1992, principally by analysis of borehole breakouts and drilling-induced tensile fractures in petroleum wells. Stress orientations are variable across the Australian continent as a whole. However, within 15 of 16 individual stress provinces defined in the Australian continent (of one to a few hundred kilometres scale), mean stress orientations are statistically significant. The stress provinces, and stress trajectory mapping, reveal that there are systematic, continental-scale rotations of stress orientation within Australia. Unlike many other continental areas, stress orientations do not parallel the direction of absolute plate motion. Nonetheless, the regional pattern of stress orientation is consistent with control by plate boundary forces, if the complex nature of the convergent northeastern boundary of the Indo-Australian plate, and stress focusing by collisional segments of the boundary, is recognized.

Geomechanical Analysis of the Naylor Structure, Otway Basin, Australia. Pre-Injection.

“…The orientation of maximum horizontal stress was determined to be 142 ºN from breakouts in the CRC-1 borehole interpreted on a resistivity image log (FMI); (van Ruth, 2007b). This maximum horizontal stress orientation is broadly consistent with the regional orientation and verifies a NW-SE maximum horizontal stress orientation in the onshore Victorian Otway Basin (Hillis et al, 1998; www.asp.adelaide.edu.au/asm).…”

Present-day stress field of Southeast Asia

“…included in the description of regional stress fields (Müller et al, 1992;Zoback, 1992;Hillis and Reynolds, 2000).…”

“…defining 14 regional stress provinces using circular statistics in a method based on that applied in other studies of plate-scale stress fields ( Figure 7; Table 2; Coblentz and Richardson, 1995;Hillis and Reynolds, 2000;Hillis and Reynolds, 2003).…”

“…Individual stress orientation indicators were weighted according to quality for the circular statistical analysis, with D-quality data receiving a weighting of one, C-quality a weighting of two, up to A-quality receiving a weighting of four (Hillis and Reynolds, 2003). The Rayleigh Test was then applied to the individual stress orientation data within each stress province to investigate whether, and how strongly developed; any preferred stress orientation is within the province (Mardia, 1972;Hillis and Reynolds, 2000). The Rayleigh Test determines the confidence level at which we can reject the null hypothesis that stress orientations within a province are random (Mardia, 1972;Coblentz and Richardson, 1995).…”

“…Mapping of the plate-scale present-day stress field can reveal key insights into the forces controlling intraplate deformation (Müller et al, 1992;Richardson, 1992;Zoback, 1992;Hillis and Reynolds, 2000). Early phases of the World Stress Map (WSM) and Australian Stress Map projects demonstrated that the first-order intraplate stress field is primarily the result of forces generated at plate boundaries, most importantly mid-ocean ridge 'push', subducting slab 'pull', trench 'suction' and resistance due to continental collision (Forsyth and Uyeda, 1975;Zoback, 1992;Reynolds et al, 2002).…”