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Big jolt an earthquake

Wednesday, 13th July, 2011

EPICENTRE: The large dots on the map show where Monday night’s earthquakes struck. EPICENTRE: The large dots on the map show where Monday night’s earthquakes struck.

There was not one, but two, earthquakes on Monday night, although the city would have only felt one tremor, according to Geoscience Australia.

It said the first earthquake happened half way between Broken Hill and Mildura and had a 2.9 magnitude. It hit around 9.50pm. 

Geoscience Australia’s Duty Seismologist, Hugh Glanville, said that this would not have been felt here.

“It was too small to be felt in Broken Hill. It is unlikely that is was felt that far north,” he said.

But the second quake of a 2.6 magnitude that struck around 11pm was the one that everyone felt.

It was located southeast of Broken Hill, and Mr Glanville said both quakes had a depth of zero kilometres, meaning they were close to the surface.

He said earthquakes of such a small magnitude don’t normally cause much damage.

“A magnitude of 4.5 is when there is minor damage,” he said.

Mr Glanville said most people would have felt the shock.

Broken Hill is in the middle of the Australia tectonic plate, and Mr Glanville said stresses on the plate and on the continent can cause minor earthquakes which relieve the stress.

There have been eight earthquakes in the local region over the last 10 years, he said.

“It is quite possible there will be a similar sized earthquake. There is a possibility of a bigger one. But there is no evidence to suggest this would happen,” Mr Glanville said.

The General Manager of the Perilya mines, Andrew Lord, said the earthquake prompted the company to evacuate the mines.

“We have a set of protocols in the event of a seismic event. We withdrew our workforce to safe areas and accounted for them,” Mr Lord said.

He said Perilya had its own seismic systems to monitor aftershocks.

There were 90-odd aftershocks but “no one would have felt them,” he said.

Mr Lord said after an inspection of the mine site, some sections were reopened but others stayed closed until 10am yesterday.

(For more information or to lodge a report about the earthquake visit www.ga.gov.au).

 

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