Aftershocks are likely following today’s 5.6 magnitude earthquake which struck 58kms from Kojonup, an earthquake expert has warned.
Geoscience Australia senior seismologist Phil Cummins said aftershocks could occur for the next few weeks, with the biggest predicted to be a unit of magnitude below the main earthquake that shook homes from Albany to Perth just before 1pm.
“So that would be 4.6 and that is still a fairly large earthquake, a moderate-sized earthquake and could be felt over a reasonable area,” he said.
“It’s always possible these could be leading up to something bigger, but I think it’s more likely we’ll see a decrease in size and frequency.”
Professor Cummins said it was unlikely Sunday’s earthquake was linked to a magnitude 3.5 quake that shook the ocean floor off Albany on Wednesday night.
He said while there may be multiple aftershocks, only the biggest would be felt due to the location.
“If you were right there in the epicentral area then you could feel quite small earthquakes, you might find that the aftershocks go on for a week or a few weeks,” he said.
“But, because in this case most people live pretty far away from the earthquake, they will only feel the large ones and they will probably die off relatively quickly, within a few days or a week would be my rough guess.
“Aftershock sequences can be different, some of them are very energetic and some aren’t.”
The Great Southern region is not known as an area of high seismicity, according to Professor Cummins.
“You get more earthquakes typically along the coast adjacent to the North West shelf or in the Wheatbelt where you had the big Meckering earthquake – those are generally thought to be the high seismicity areas in Western Australia.
“But there have been pretty large earthquakes here in the past. Over the past couple of decades there have been earthquakes in towns near Norseman, there was one off shore just a week or so ago.”
He said the earthquake would have been the result of forces exerted 1000s of kilometres away at the boundaries of the Australian tectonic plate in Indonesia and New Zealand.
“They will slowly build up to the point where they exceed the frictional strength of faults in the crust and that’s what’s happened here,” he said.
“I haven’t heard of any reports of damage, the earthquake is big enough to cause damage but it is unlikely to have done so because it occurred in such a remote area.”
The last magnitude 5.6 earthquake occurred in 2016 near Norseman.