Geophysical survey as a part of a multi-tiered investigation in fault characterization and dam seismic hazard assessment – a case study from South Australia

Fault characterisation and definition of its activity is an important task in defining the seismic hazard for dams. This is especially the case when some evidence of fault activity exists. A multidisciplinary approach (i.e. geomorphology, structural mapping in the spillway, seismic reflection and refraction, paleoseismic trenching, downhole geophysics and geotechnical boreholes) including use of lidar and bathymetry investigation have been undertaken to inform the overall dam safety and seismic hazard assessment of a dam site in South Australia. This multi-disciplinary investigative approach has led to new active strands of an active fault being recognised, which pass near the main dam and close to a proposed saddle dam, presenting challenges to the dam upgrade design and ongoing dam safety. The geophysics segment of investigation (Seismic Reflection, Seismic Refraction, and Downhole geophysics) has improved understanding of seismic risk and assisted in developing the dam upgrade design.