A small area in Western Australia's south has recorded more than 40 earthquakes, including a 4.7 magnitude this morning, in what experts have called a rare earthquake swarm.
Geoscience Australia recorded a 4.7m earthquake north-west of Wagin just before 5.30am on Tuesday, which was felt as far away as Perth and Albany.
Gaye Martens-Bowley felt the earthquake from her home in Busselton.
"Roof shook, lounge chair moved and my coffee had waves in it," she posted on social media.
Since January 5, the area around Arthur River, Darkan and Wagin - about 200 kilometres south-east of Perth, has been shaken regularly.
Three larger tremors, the strongest of which was a magnitude 3.5, hit on Sunday.
Farmer Laura Abbott said she felt the earthquakes, which were felt as far south as Albany — 200km away — on Saturday.
"The windows were rattling and our cupboards were rattling — you could kind of hear it coming too," she said.
"The earth shook for a while then calmed down.
Ms Abbott said the quakes were unnerving and caused minor damage.
"My parents had just recently renovated their house and the concrete that they've just got done has cracked a little bit," she said.
What is an earthquake swarm?
Geoscience Australia senior seismologist Hugh Glanville said a swarm was a sequence of earthquakes in a localised area.
"In the past week they've had 26 in that area," he said.
"It's what's known as an earthquake swarm, where we have a lot of medium-sized earthquakes.
"Swarms aren't a common type of activity across the world.
Mr Glanville said the northern drift of the Australian plate caused stress across the continent that could spark earthquakes away from plate boundaries.
"The Australian plate is moving northwards at about 7 centimetres per year," he said.
"A lot of that [energy] is released along the boundary, but some transfers into the continent and is released — most commonly through these small to medium-sized earthquakes."
Australia averages 700 earthquakes each year, but most are felt only within a 10- to 20-kilometre radius of the epicentre.
Mystery surrounds quake hotspot
The south-west corner of WA is a particularly active earthquake zone, but researchers are still unsure why.
A series of earthquakes near Lake Muir in 2018 — the largest a magnitude 5.4 that was felt as far away as Perth and Albany — prompted the installation of seismic monitoring devices across the region.
"It's one of the hotspots of earthquake activity in Australia," Mr Glanville said.
"It is a hotspot of activity … high rates of seismic activity and known to host larger earthquakes such as [the town of Meckering's in 1968].
