100 earthquakes in a month

Cut and Paste from the msnnine web site.


There's been a whole lot of shaking going on, of the earthquake variety, in a small West Australian wheatbelt town.

Beacon, 320km north-west of Perth, has had roughly 100 earthquakes in the last month, Geoscience Australia seismologist Phil Cummins said on Sunday.

Between three and six earthquakes registering three and above on the Richter Scale had been detected in the area in the last month.

"A few of those have been in the mid to high fours," Mr Cummins said.

The largest, which registered nearly five on the Richter Scale came within 24 hours of earthquakes in Melbourne and off the coast near Broome on Friday.

"That could be felt over a wide area, it could even cause damage if you were right on top of it, minor damage," Mr Cummins said.

"Certainly these were as big as the ones that shook all of Melbourne.

"I think for the people in the wheatbelt who are used to earthquakes, they probably don't get too upset about it but you take the same earthquake and put it in Melbourne where people haven't experienced it and people can be very upset."

The earthquake clusters, known as swarms, were not unusual for the wheatbelt area but what was unusual was the migration of the swarms around the wheatbelt.

Similar patterns were noted in Koorda in 2003 to 2005 and Burrakin between 2000 and 2002.

"These ones like the Beacon case where you seem to get several moderate earthquakes and then lots and lots of smaller quakes, it is a bit unusual," Mr Cummins said.

"It's called a swarm because it doesn't follow the typical foreshock, minishock, aftershock pattern or at least it doesn't seem to," he said.

"That's this migrating swarm, I'm not sure I've ever heard of that before.

"For that area it would seem that this behaviour is not atypical."

Seismologists were uncertain if the swarms were related to larger earthquake events such as the wheatbelt's Meckering earthquake in 1968, which registered 6.8 on the Richter scale.

The seismic activity could be relieving stresses and avoiding larger earthquakes or it could result in a big rupture.

"We just don't know ..." Mr Cummins said.

"The big question really is whether it has any relationship to larger earthquakes which occur."

How long the seismic activity lasts for the residents of rural Beacon is anyone's guess, Mr Cummins said.

"They seem to die out gradually, we don't really know that much of what to expect, I mean Burrakin went on for a couple of years, Koorda sort of gradually started up and faded out," he said.

"It could continue for a while."






AAP 2009