Prediction of the present-day stress field in the Australian continental crust using 3D geomechanical-numerical models

摘要

The Australian continent has an enigmatic present-day stress pattern with considerable regional variability in maximum horizontal stress (S-Hmax) orientations. Previous attempts to estimate the Australian S-Hmax orientation with geomechanical-numerical models indicate that plate boundary forces provide the major controls on the contemporary stress orientations. However, these models do not satisfactorily predict the observed stress orientation in major basins throughout eastern Australia, where the knowledge of the present-day crustal stresses is of vital importance for development and management of different types of geo-reservoirs. In addition, a new comprehensive stress-data compilation in Australia, which contains 2150 data records and is the key dataset for model calibration, provides motivation to construct a new geomechanical-numerical model for Australia. Herein, we present a 3D geomechanical-numerical model that predicts both the S-Hmax orientation and the relative stress magnitudes throughout the Australian continent. Our best-fit model, with mean absolute deviation of 15 degrees, is in good agreement with observed S-Hmax orientations and the stress regime in most areas, and shows a much better fit in areas where the stress pattern was unable to be predicted by previous published attempts. Interestingly, the best-fit model requires a significant push from the western boundary of Australian continental model, which is possible supporting evidence for the east-west-oriented mantle drag postulated by state-of-the-art global convection models, or may be generated by the excess of gravitational potential energy from Tibetan Plateau, transferred through the Indo-Australian Plate. Hence, our modelling results provide a good first-order prediction of the stress field for areas where no stress information is currently available and can be used to derive initial and boundary conditions for local and reservoir-scale 3D geomechanical models across Australia.