Site Classification and VS30 Determination for Seismic Hazard Evaluation in the SWAN Seismic Network, Western Australia

 Seismic site classification is essential for seismic hazard analysis as it helps constrain the impact of local geological conditions on the near-surface seismic-wave propagation and observed ground motion. The Southwest Australia Seismic Network (SWAN) temporary array was established to record local earthquakes for seismic hazard applications and to improve rendering of the 3D seismic structure of the crust and mantle lithosphere in southwestern Australia. Notably, the SWAN project has recorded significant seismic events, including the 2022 Arthur River earthquake sequence and the 2023 MW 5.0 Gnowangerup earthquake. These earthquakes, together with other well-recorded events across the SWAN network, offer a rare opportunity to assess the utility of published ground-motion models (GMMs) for large-magnitude earthquakes, thereby significantly improving seismic hazard assessment in the region. Moreover, the importance of site classification is underscored as it is a critical component of GMMs, and can substantially enhance the accuracy and reliability of these models. This study uses microtremor survey methods to estimate the shallow shear-wave velocity profiles and VS30 values, which are the primary factors for site classification at seismic stations. Microtremor array measurements, such as high-resolution frequency-wavenumber and modified spatial autocorrelation methods, were utilized to analyse ambient vibrations, producing detailed dispersion curves for each station. To enhance the depth accuracy of velocity profiles, ellipticity curves were extracted using the RayDec method and jointly inverted with the dispersion curves. Additionally, OpenHVSR software was employed for the inversion of single-station ellipticity curves.

Citation: Ebrahimi, R and Allen, TI 2024, Site classification and VS30 determination for seismic hazard evaluation in the SWAN seismic network, Western Australia, in South West Australia Network (SWAN): passive seismic imaging and hazard analysis compiled by RE Murdie and MS Miller: Geological Survey of Western Australia, Report 255, p. 58–67