An investigation of local site effects in Adelaide, south Australia: learning from the past

Three major seismic events have damaged the Old Exchange Building, Adelaide, southern Australia. The building was graced by the Britannia statue on the parapet of the building. The statue lost its arm during the 1897 Beachport earthquake and bowed its helmeted head during the 1902 Warooka seismic event. It was removed after the 1954 Adelaide earthquake. Local site effects contributed significantly to the destruction of the Britannia statue. This paper investigates and presents the historical local site effects with respect to the Old Exchange Building. Synthetic ground motion time histories of the past three seismic events are generated and confirm the suitability of the method. Representative 1D soil profiles are developed and validated. Site response analysis was then carried out at the Old Exchange Building site to obtain the seismic parameters at the investigated site. The results are compared against historical intensity maps of the events, which are assumed as the actual spectral accelerations during the events. Hazard spectra and amplification triggered by the seismic events are deduced. This study reveals the significance of local site effects by an amplification factor of up to 3.4 that led to the destruction of the Britannia statue.