SYDNEY, 20 July 2004 — Australia is shaken by about 200 tremors each year, but most register only about 3 on the Richter scale and usually occur in the outback, scaring a few birds and kangaroos.
But scientists say a major earthquake could strike Australia’s largest city Sydney, population 4.5 million, and even a moderate quake could cause devastation and death.
The strongest quake on record in Australia registered about 6.9 on the Richter scale, matching the strength of Japan’s Kobe earthquake in January 1995 that killed more than 6,400 people.
“Large earthquakes have occurred in sparsely populated areas. You can’t discount that possibility, that a large earthquake might occur in the Sydney area,” said Phil Cummins, head of the earthquake hazard team at government agency Geoscience Australia.
In fact, every five years or so a potentially disastrous earthquake of 6.0 or more on the Richter scale rocks Australia and a quake as high as 7 is expected to occur every 100 years.
And scientists say the larger quakes are more likely to hit the edges of the Australian continent where the vast majority of the population lives.
Australia’s most damaging earthquake, a moderate 5.6 on the Richter scale, occurred in December 1989. The quake struck the coastal coal-mining city of Newcastle, killing 13 people, injuring 130 and causing insured losses of nearly A$1 billion.
Total estimated losses were $4 billion, including uninsured losses, damage to infrastructure and community disruption, according to Emergency Management Australia, a government disaster management body.
Newcastle, with a population of more than 300,000, is about 140 km north of Sydney.
Earthquakes, bushfires, cyclones and floods have the potential to cause havoc in Australia and the largest exposure to most of these risks is Sydney, given its status as the country’s center of commerce and large population.
In the world of earthquakes, risk analysts play what they call “the catastrophe game” to figure out the odds of a quake hitting a city like Sydney.
There is only a small chance of a major earthquake striking Australia’s eastern seaboard. But, as the Newcastle quake showed, they can happen and can cause extensive damage.
Regulators, particularly after the massive losses caused by the Sept. 11 attacks on the United States, require Australia’s insurers to buy a high level of cover.
“(Germany’s) Munich Re insurance were here almost a year ago. They cover the major disasters in the region. That was one of their major scenarios, a large earthquake in Sydney. That was one of their major concerns,” Cummins said.
Insurance Australia Group Ltd, the country’s largest insurer, has cover for earthquake losses of up to A$3 billion ($2 billion) for 2004. That figure includes coverage for quakes in nearby New Zealand, where the much greater likelihood of earthquake damage is also covered by a state-funded disaster insurer.
“Insurers have to buy cover to a level that means there is no more than a 1-in-250 chance of it being insufficient. You can assume that the risk is believed to be no more than this (A$3 billion),” an IAG company spokesperson said.
The frequency of earthquakes is lower in Australia than in its Asia-Pacific neighbors because the continent sits on the Indo-Australian tectonic plate, rather than on a volatile edge.
Earthquakes are most common where different tectonic plates meet, for example in earthquake-prone New Zealand to the southeast, which straddles the Indo-Australian and Pacific Plates.
Intraplate earthquakes, like those in Australia and continental North America, are less common and do not follow a pattern. They can also feel more violent, because intraplate earthquakes generally occur closer to the earth’s surface.
When a large earthquake occurs within 10 km of the Earth’s surface, the fault may rupture through the rocks that make up the Earth’s surface and open up a long jagged rent.
Australia has had five such fault breakages in the past 30 years, more than any other country. All five are in remote areas away from major population centers.
Hidden thrust faults pose hazards to buildings, roads, railways and pipelines which no one can truly calculate. And just like Kobe, an Australian earthquake is likely to have a shallow epicenter, ensuring maximum damage.
In August 1994, an earthquake of about 5.6 on the Richter scale rattled Sydney and the east coast but it lasted for only about 10 seconds. Still, the tremor was felt over a 300 kilometers stretch from Wollongong to the south to Sydney and Newcastle in the north.
