Detail that prevented earthquake disaster
Victoria’s historic earthquake triggered sweeping evacuations of office buildings in Melbourne, but one detail proved crucial in the city avoiding a catastrophe.
Waves of aftershocks could rattle Victoria for the coming weeks and months after the biggest earthquake in recorded history shook the state on Wednesday.
The 5.9 magnitude tremor rocked buildings about 9.15am, with the epicentre recorded near Mansfield about 115km northeast of Melbourne.
Workers were huddled in groups on the streets of Melbourne CBD as office buildings were evacuated, while vibrations were felt as far as Adelaide, Canberra and even Launceston.
The worst damage was recorded at the Betty’s Burgers building in Chapel St, Windsor, where bricks and debris spilt on to the footpath and road below, but emergency management authorities warned it would have been a “disaster” had the quake struck closer to the city.
Victorian SES chief officer Tim Wiebusch said more than 108 calls for help were made to the service, mostly for help with building damage – No one had been reported as injured.
“If the earthquake occurred in a densely populated urban area, it would have been a different result,” Mr Wiebusch said.
University of Melbourne associate professor of earthquake science Mark Quigley also said Melbourne was lucky to escape major damage and catastrophe.
“You are seeing damage in Melbourne 150 kilometres away from the earthquake. If we were to get one of this magnitude beneath an urban centre, the damage would be catastrophic,” he said.
Most damage to the city was minor, with cases of crumbling brick chimneys, cracked walls and internal breakages recorded in homes across the city. Residents also reported birds falling silent as the tremor rumbled through the suburbs.
State Emergency Management Commissioner Andrew Crisp warned that aftershocks were likely but unlikely to be as severe as the initial jolt.
University of the Sunshine Coast geotechnical engineering senior lecturer Dr Adrian McCullum warned geological maps of the area where the epicentre was recorded showed a “large number of faults”.
“Thus it appears like an area where the release of compressive stress via an earthquake might be probable,” he said.
“These earthquakes occur because the continental plate on which Australia sits is moving north at about 7cm per year.
“This builds up compressive stress within the Australian Plate – This stress is occasionally released along preferred areas, typically, pre-existing fault lines, where the earth has sheared because of these stresses.”
A total of 185 people died in 2011 when a 6.3 magnitude earthquake struck Christchurch in New Zealand.
While just slightly stronger than Wednesday’s quake, the Christchurch vibrations reverberated at 5km beneath the ground in the major city compared to 10km in Victoria’s regions.
Australia’s most deadly quake, on December 28, 1989, in Newcastle had a magnitude of 5.4. Because its epicentre was close to urban areas, the disaster killed 13 people, injured more than 160 and left a $4 billion damage bill.
Power was lost to more than 35,000 Victorian homes in metropolitan Melbourne and the northeast of the state on Wednesday morning. Most were back online by midafternoon.
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