The most damaging
earthquake in Australia's history was caused by humans, new research
says. The magnitude 5.6 quake that struck Newcastle, in New South
Wales, on December 28, 1989, killed 13 people, injured 160, and
caused 3.5 billion U.S. dollars worth of damage.
That quake was triggered by changes in tectonic forces caused
by 200 years of underground coal mining, according to a study by
Christian D. Klose of Columbia University's Lamont-Doherty Earth
Observatory in Palisades, New York.
The quake wasn't enormous, but Australia isn't generally considered
to be seismically active and the city's buildings weren't designed
to withstand a temblor of that magnitude, Klose said. All told, he
added, the monetary damage done by the earthquake exceeded the total
value of the coal extracted in the area. Klose presented his
findings at a meeting of the American Geophysical Union in San
Francisco, California last month.
"The removal of millions of tons of coal
from the area caused much of the stress that triggered the Newcastle
quake," Klose said.
He said his modelling
and simulations showed mining "was likely to trigger the . . .
Newcastle earthquake at a depth of 11.5 kilometres after 188 years
of black coal mining" - the same depth that Geoscience Australia
gives for the epicentre.
But even more
significant was groundwater pumping needed to keep the mines from
flooding. "For each ton of coal produced, 4.3 times more water was
extracted," Klose said.
Dr Klose said "dewatering" mines removed
millions of tonnes of groundwater from Newcastle over the years,
adding to "destabilisation in the Newcastle fault."
Other mining operations, he added, sometimes require as much as 150
tons of water to be removed for each ton of coal produced. "So this
is on the low end," he said.