A recent earthquake in the Sydney area has belied the popular misconception that Australia and its building stock are safe from seismic risk.
The 3.5 magnitude earthquake struck the Campbelltown area in southwestern Sydney at around 7:15 am on Tuesday, October 8. Campebelltown is located only 50 kilometres from Sydney’s bustling central business district, while the epicentre of the earthquake itself was only 30 kilometres away from the Lucas heights nuclear reactor.
Although Australia’s geographic location at the centre of a tectonic plate means it is at a greatly reduced risk of earthquakes, seismological experts say this does not mean that the country is entirely impervious to such natural disasters.
According to professor Mike Griffith, a structural engineer from the University of Adelaide, the risk of minor earthquakes in Australia is far greater than most of its urban denizens realize.
“There are probably faults close to every city that we don’t know anything about,” said Griffith, who led an investigation into the types of buildings which best weathered the Christchurch earthquakes in 2010 and 2011.
Adjunct professor Kevin McCue from the Australian Seismological Centre told The Fifth Estate that Australia’s remoteness from tectonic boundaries in no way spares it from seismic risks.
“While 90 per cent of earthquakes occur on plate boundaries, 10 per cent occur within the plate, and these earthquakes can cause major damage,” he said.
According to McCue, the 6.3 magnitude earthquake which devastated Christchurch in 2011 is an example of the type of intraplate earthquake which could potentially strike an Australian city. Closer to home the 1989 Newcastle earthquake – which measured 5.6 on the Richter scale and is one of Australia’s worst natural disasters – is a further example of an intraplate earthquake which can strike the country, although popular perception generally deems it to have been a freak incident.
While the general public may be largely oblivious to the threat posed by earthquakes to Australia’s urban centres, the insurance industry remains acutely aware of the risks they bring. Global insurer GBE recently announced that it considers an earthquake in Sydney to pose the single greatest risk to its operations in Australia, potentially incurring insured losses of around $20 billion.
A study led by Michael Griffith in conjunction with the University of Auckland and Italy’s University of Pavia found that a key measure for reducing the damage caused by earthquakes in urban areas is the retrofitting of older buildings.
Australia and New Zealand both built unreinforced masonry buildings until as recently as the 1930s, meaning their walls weren’t braced by reinforcing beams.
Many Australians continue to live in such buildings, which are especially dangerous in the event of an earthquake due to both their innate structural vulnerabilities as well as their age.
According to Griffith, simple measures such as steel braces and straps can be used to secure chimneys and parapets to roofs, although the reinforcement of walls requires greater effort and cost. The study found that old buildings in Christchurch needed to have their walls strengthened to two thirds of standards in order to be safer and more resilient in the event of an earthquake.
Broader efforts to ensure that new buildings in Australia are earthquake proof remain fraught with difficulty, however, due to complacency and lack of awareness.
McCue pointed to ignorance amongst building owners about the need to meet the 2007 Australian Earthquake Loading Standard despite the additional expense incurred in meeting the standard estimated to be just 0.05 per cent of the cost of “total building task.”
A further problem is a lack of qualified earthquake engineers in Australia, given the general perception that such natural disasters aren’t a problem for the country, meaning there is a lack of informed regulators capable of determining whether or not buildings are in compliance with standards.