Earthquake Ground Shaking Susceptibility of the Botany Area, New South Wales
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Dataset Identification:
Resource Abstract:
An earthquake of magnitude 6.0-6.5 in the Sydney region of Australia is viewed by the global insurance community as one of
the top 40 risks it faces worldwide from natural disasters . The high ranking of this perceived risk is due to the high population
density, standards of construction and the level of insurance exposure in Sydney. Consequently, earthquake hazard and risk
in Sydney is an important issue, and one that requires a focused and detailed study in order for the implications of such
an earthquake to be fully understood.The presence of regolith (soils, sediments and weathered rock) can dramatically affect
the level of ground shaking experienced during an earthquake. The relatively soft materials that constitute regolith tend
to have low seismic velocities that amplify ground shaking during an earthquake, increasing the potential for damage to buildings
and other infrastructure in the affected area. Therefore, models of the response of regolith to an earthquake (referred to
as site response) form an integral part of any earthquake risk assessment.This report documents a preliminary study of potential
ground motion amplification due to the regolith in the Botany area of Sydney, Australia. Botany was chosen due to the presence
of a significant thickness of regolith and a high value and concentration of critical infrastructure. This report is intended
to highlight the potential for significant levels of amplification within the study area, and draw attention to the need for
more work on assessing the actual earthquake risk faced by the Sydney region.In order to determine the amount of ground motion
amplification that could be seen in the Botany area, the regolith was classified into a series of four site classes. These
regolith site classes are differentiated in terms of geotechnical properties that control ground shaking potential. This classification
was based upon published and unpublished geotechnical data as well as seismic velocities obtained by Geoscience Australia.
Once geotechnical models were defined for each regolith site class, amplification factors were calculated using a vertically
propagating shear wave model. This model accounts for the softening and critical damping of the regolith column during large
earthquakes. The results demonstrate that there is significant potential for amplification of ground shaking within the study
area. For example, the site class that covers the vast majority of the study area has a maximum amplification factor greater
than 3.0 at a fundamental site period of approximately 0.5 s. This period of motion would be expected to strongly affect the
structures in the study area.The modelled amplification factors suggest that, should an earthquake impact the area, the potential
for high levels of ground shaking would be dramatically increased due to the properties of the local regolith. An earthquake
similar to the event experienced in Newcastle in 1989 was simulated, in order to demonstrate the potential amplification effect
of the regolith during an earthquake. Whilst this simulation is in no way a full probabilistic risk analysis of the area,
it does demonstrate that the amplification of ground shaking could cause response spectral accelerations in excess of 1.0
g, at periods of vibration that would be expected to cause damage to structures in the area.It is important to emphasise that
this work is intended to provide a point of focus to initiate discussion rather than be a definitive seismic hazard assessment
product. The results have been derived with limited geotechnical data, and without a detailed analysis of the uncertainties
present within either the data or the modelling process. Nevertheless, this work does provide a starting point for recognising
and addressing the potential risk that earthquakes pose to the study area.
Citation
Title Earthquake Ground Shaking Susceptibility of the Botany Area, New South Wales
Metadata hierarchy level name:
nonGeographicDataset - GA Publication - Record
Metadata language
eng
Metadata character set encoding:
utf8
Metadata standard for this record:
ANZLIC Metadata Profile: An Australian/New Zealand Profile of AS/NZS ISO 19115:2005, Geographic information - Metadata
standard version:
1.1
Metadata record identifier:
d4ed81b6-de0e-3105-e044-00144fdd4fa6
URI for dataset described:
> http://www.ga.gov.au/metadata-gateway/metadata/record/75265/
Metadata record format is ISO19139-2 XML (MI_Metadata)