Geological and historically based numerical assessment of seismic hazard in an evolving block cave mine

Authors: Orrego, C; Viegas, G; Tennant, D; Stonestreet, P

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DOI https://doi.org/10.36487/ACG_repo/2465_77

Cite As:
Orrego, C, Viegas, G, Tennant, D & Stonestreet, P 2024, 'Geological and historically based numerical assessment of seismic hazard in an evolving block cave mine', in P Andrieux & D Cumming-Potvin (eds), Deep Mining 2024: Proceedings of the 10th International Conference on Deep and High Stress Mining, Australian Centre for Geomechanics, Perth, pp. 1179-1192, https://doi.org/10.36487/ACG_repo/2465_77

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Abstract:
We developed a workflow to calibrate and forecast seismic hazard and its evolution, generated by seismic activity in known geological structures located next to an evolving block cave mine and corresponding mineinduced stresses. This approach is particularly relevant in caving mines with several mining sectors, where learnings from rock mass behaviour and the associated seismic response of the earlier blocks are used to characterise, back-analyse and forecast future blocks’ seismic hazard, and can also be applicable to other types of underground mines. The methodology considers the geological/geotechnical characterisation of the geological structures such as continuity, planarity, roughness and other associated properties as observed in drillcore and mapping data. Together with observed seismicity, it allows for the ranking of structures by their potential to generate large seismic events. The methodology relies heavily on numerical modelling to track the changes of the stress field due to the cave evolution and its effects on the identified geological structures. The structures are modelled explicitly using interfaces to assess the slip potential and estimate the associated seismic source parameters. The geomechanical model is calibrated using the observed seismicity during previous cave development and then used to forecast (forward analysis) the maximum slip potential of currently seismically inactive structures due to stress evolution (and resulting unclamping) once future block caves are developed. Based on the estimated time-evolving maximum slip potential and associated seismic source parameters, site-specific ground motion prediction equations are used to forecast peak ground motion for critical infrastructure and other sites of interest, allowing an early assessment of seismic hazard based on the geological/geotechnical characteristics of the existing geological structures. The seismic hazard assessment is developed during the study/design stages, allowing for testing multiple scenarios and aiding in minimising the seismic hazard in areas of interest.

Keywords: seismic hazard, numerical modelling, ranking of seismic structures, block caving

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