BHP Mount Arthur Coal

The unique seismotectonic properties of this site required these considerations to be applied:

• For a tailings dam, the construction is usually carried out in stages so that the height and elevation will build up and vary over the mine life. The shear wave velocity of embankment materials/tailings increases with depth due to increases in confining stresses and density, resulting in a non-linear depth profile. Furthermore, the shear wave velocity of the embankment materials/tailings may change during the course of an earthquake due to strain-softening of the materials as a result of repeated cyclic loading. Therefore, the tailings dam’s (storage facility) natural period/ frequency cannot be adequately represented by a constant value that could be used for derivation of the CMS conditioned on the occurrence of a target spectral acceleration.
• Three seismic source seismotectonic models were used (AUS6, DIM-AUS and NSHA13) to account for the epistemic uncertainties inherent in seismotectonic models with guidance on suitable weights as applied in the NSHA18 project.
• To consider both aleatory variability and epistemic uncertainty between the Ground-Motion models (GMM) several were used with different weights. The GMM were the same as those used in the 2018 National Seismic Hazard Assessment and are recommended by ANCOLD (2019). In this study, Ground Motion Models were selected based on applicability to the south-east Australian rock conditions and in line with NSHA18 Project’s approach.