Seismic measurements made for earthquake hazard
24 May 2012
Residents in the Sydney Basin will have a better understanding soon of the possible damage from earthquakes in the region.
Seismologists from Geoscience Australia and Monash University recently carried out a survey of seismic shear-wave velocities under the Sydney and Newcastle metropolitan areas. Shear waves are a form of seismic wave in which the particle motion is perpendicular to the direction of seismic wave travel and are particularly damaging to buildings and infrastructure.
The seismologist leading the project, Clive Collins said that shear-wave velocity profiles help scientists estimate the amount of ground shaking which occurs under buildings and other infrastructure during an earthquake.
“Local site conditions, such as the thickness and stiffness of the underlying sediments, are important factors to investigate because the degree of ground shaking can be amplified by deep, soft sediments which can result in greater damage to buildings,” he said.
Mr Collins said that the characteristics of specific sites can be measured using the Spatial Auto-Correlation (SPAC) method which makes use of existing seismic vibrations that are generated by traffic, wind, ocean waves and other sources.
“The seismic data was obtained on a 100 metre triangular array of recorders at sites in Newcastle and Sydney, as well as at four permanent seismograph stations of the Australian National Seismic Network,” Mr Collins said.
“A variety of sites were surveyed based on previous investigations and observations of building damage during the 1989 Newcastle earthquake to characterise the sediments and shallow rocks underlying the urban areas,” he said.
The data will be interpreted to produce shear-wave velocity profiles for each site which will then be used to estimate the characteristics of the underlying sediments and establish what are termed site classes based on the profiles in specific areas of the Sydney Basin. This information can also be used in other urban areas of Australia.
“The data obtained will help agencies and individuals responsible for urban planning and infrastructure management to mitigate the possible effects of seismic activity,” Mr Collins said.
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