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Abstract
The majority of published in-situ stress information in the Australian continent is confined to petroleum provinces where industry technologies facilitate the capture of contemporary crustal stress information. In contrast, the stress pattern of non-petroleum regions such as the Flinders and Mount Lofty Ranges in South Australia, where intraplate deformation is localised, has not been investigated comprehensively so far. The ongoing activities of the mining industry in South Australia has enabled us to access recently drilled boreholes for image logging techniques that have typically been under-utilised by the mineral sector. Herein, we conduct stress analysis by analysing borehole image logs from 16 boreholes in the basement rocks of South Australia as well as two geothermal wells and one coal seam gas well in South Australia’s northern Flinders Ranges, the Gawler Craton and the Eyre Peninsula. The resulting dataset of stress orientations is further accomplished by including recent seismological observations, which provide crustal stress information derived from focal mechanism solutions. The results of this study suggest a regional E–W orientation of the maximum horizontal compressive stress that is consistent with numerous observed neotectonic structures in this region. The focal mechanism solutions in this study suggest that the majority of events occur in a thrust faulting stress regime, which is consistent with the observed Quaternary fault scarps. However, our data compilation also indicates the presence of strike-slip and normal faulting stress regimes in the region, which has not been suggested extensively before this study.
The results of this study suggest a regional E–W orientation of the maximum horizontal stress in the Flinders and Mount Lofty Ranges. Focal mechanism solutions of earthquakes suggest that the majority of events occur in a thrust faulting stress regime. However, our data also indicate the presence of strike-slip and normal faulting stress regimes in the region, which has not been suggested extensively before this study.
Acknowledgements
Contributions by the first and second authors form part of ARC Discovery Project DP120103849, and ASEG Research Foundation Project RF13P02. The authors would like to thank the funding by AuScope’s AGOS Subsurface Observation program for running borehole image logs in mineral wells. DET CRC is thanked for providing the raw data of Brukunga-1. Caleb Ames is thanked for his cooperation and running the image tools in mineral wells. Phil Cummin is thanked for his cooperation on the temporary network deployment in south-central Australia. Department of State Development (DSD) - South Australia is acknowledged for providing the borehole image logs of the Blanche-1 and Paralana-2 geothermal wells. We would like to thank the Ikon Science in Adelaide (formerly JRS Petroleum Research) for the use of their JRS suite. We also specially thank John Reinecker and an anonymous reviewer of this article for their constructive comments.