Earthquakes pose a major risk, with their immense power taking lives, destroying buildings and disrupting societal functioning. This case study outlines a methodology for building realistic earthquake disaster scenarios for major cities, using Adelaide as an example. We analyse an earthquake of magnitude 6.0 occurring on the Para fault at a depth of seven kilometres and with its epicentre seven kilometres from Adelaide’s CBD.
This study is part of a broader research program from Risk Frontiers for the Bushfire and Natural Hazard CRC. It seeks to deliver a suite of scenario simulations that investigate realistic disaster scenarios, scenarios that lie well beyond emergency managers’ recent experience. These scenarios will help emergency manager’s stress test their operations by revealing blind spots and vulnerabilities in their strategic planning.
Historical experience
Despite its low seismic activity, Australia is more vulnerable to earthquakes than one would expect by virtue of its concentration of population and the value of its building stock, much of which is structurally unable to withstand even moderate seismic shaking. The 1989 magnitude 5.6 Newcastle earthquake rates as one of the costliest natural disasters in Australia, despite its low magnitude, with its epicentre occurring close to the city’s CBD.
But what would happen now if one of Australia’s more populous cities were struck by an earthquake of a similar magnitude?
The 1954 magnitude 5.6 Adelaide earthquake affords an example of a close call. Until the Newcastle quake, this was the most destructive earthquake to have hit Australia. Its epicentre lay far from developed areas at the time, but today would now lie within densely developed areas.
No lives were lost in the 1954 quake and there were only three recorded injuries. Many houses were cracked and heavy pieces of masonry fell from parapets and tall buildings in the city. One of Adelaide’s earliest buildings, the Victoria Hotel, partially collapsed. Other major buildings that were severely damaged included St Francis Xavier Cathedral, the Adelaide Post Office clock tower and a newly completed hospital in Blackwood, which sustained major damage to its wards and offices. The Britannia statue in Pirie Street was badly damaged, and since it had also been similarly damaged in the 1897 Beachport and 1902 Warooka earthquakes, the clock in the statue was permanently removed. The Troubridge Island Lighthouse off the south east corner of the Yorke Peninsula shut down after the quake damaged its generator, while the Cape St Auburns Lighthouse on Kangaroo Island began flashing irregularly.
Figure 1 Residential damage: destruction as a percentage of replacement value of the local building stock
Methodology
In order to develop a scenario we employed a suite of models that consider risk a function of:
Hazard: in the case of earthquake, this describes how seismic waves cause ground motions in locations away from the fault as a function of its magnitude and distance from the epicentre
Vulnerability: how buildings are impacted by seismic ground motions
Exposure: where buildings are located and whether or not they are occupied at the time of the event.
What is special about this exercise?
Hazard modelling
Most earthquake loss models tend to use a single-variable such as peak ground acceleration to estimate damage. Peak ground acceleration corresponds to the lateral impulsive force exerted by ground motions on a building; however, damage is also a function of how quickly or slowly that force is applied, which is in turn related to the distance from the source and local soil conditions, as well as a building’s construction details and height. For example, low frequency ground motions of a one second period will affect a 10 storey building more than shorter buildings, which will respond more to high frequency ground motions. This modelling exercise takes all of this into consideration by using a multi-parameter vulnerability model, which corresponds to the full response spectrum of the ground motion – this is the only earthquake loss model of its kind.
Exposure modelling
Another important feature of our modelling is high-resolution exposure information using the Geocoded National Address File. For construction categories we used the National Exposure Information System from Geoscience Australia. This exercise also requires information on soil types, location of essential facilities and population from a number of sources (Australian Bureau of Statistics, Roadnet and Risk Frontiers’ in-house information)
Results
Buildings
A large number of buildings are expected to sustain severe damage, with Figure 1 showing the extent of the damage to residential addresses. It is predicted that an earthquake like this would result in a large number of homes being destroyed or unsuitable for occupation.It is assumed that a building is located at each address.
People
An earthquake can occur at any time and this is important when estimating casualties. For this exercise we have modelled an event that occurred at 2am, when most people are at home, and another at 2pm on a weekday, as these times were expected to result in the highest casualties. For both time periods, casualties could be in excess of 300, with over 100 life-threatening injuries expected. Basic medical aid that could not be self-treated is estimated to be required for approximately 5,000 people.
We have also modelled damage and disruption to infrastructure and essential facilities – hospitals, schools and emergency services facilities.
The analysis portrays a potentially devastating scenario for the population and the economy of Adelaide. Worst-case scenario planning such as this will help emergency services plan and prepare for natural disasters beyond our current experience.