Southern WA Farmers Rattle by Unprecedented Earthquake Swarm
Farming communities in the southern reaches of Western Australia are experiencing an unusual and persistent phenomenon: an ongoing swarm of earthquakes. Since the beginning of February, more than 70 tremors have shaken the region, leaving residents bewildered and seismologists intrigued.
The epicentre of much of this seismic activity appears to be concentrated in an area near Gnowangerup, a town situated approximately 345 kilometres south-east of Perth. This farming hub alone registered a dozen earthquakes on a single Monday, followed by a magnitude-3.1 event the very next day. For locals like Timm House, a farmer whose property lies close to the affected zone, the initial tremors were easily mistaken for everyday occurrences.
“I reckon there was a fair few early on that we didn’t realise that’s what they were, just thought it might have been the house creaking,” Mr House recounted. “Then you do get the heavier ones which make a good bang and [Monday] night all cutlery rattled in the sink, that was as heavy as we’ve had.”
The quakes have been occurring at all hours, disrupting the daily lives of residents. Mr House described experiencing a magnitude-three quake around 10 o’clock on a Monday morning, which was distinctly felt. Later that night, at 1:30 AM on Tuesday, a tremor measuring 2.9 or 3 magnitude woke him and his family. This was followed by a flurry of another 10 to 11 smaller quakes in the subsequent few hours. Fortunately, these tremors have largely ranged between magnitude 2 and 3, and no damage has been reported. The vibrations have been felt as far afield as Katanning, a town located about 60 kilometres from Gnowangerup.
The Mystery Behind the Tremors
Geoscience Australia’s senior seismologist, Phil Cummins, has indicated that the current seismic activity is most likely an earthquake swarm. This differs from a foreshock sequence, which could precede a much larger earthquake. An earthquake swarm is characterised by a series of small to moderate magnitude earthquakes, with the frequency eventually tapering off.
“The frequency has ramped up in this last month, but I don’t really see the sharp increase that one might expect from a foreshock sequence,” Dr Cummins explained. “We always have to be cautious about this, but I don’t see any reason to expect a really large earthquake to occur anytime soon. But I would expect this [earthquake swarm] to go on for at least a little while longer.”
This is not the first time the region has experienced such seismic activity. A similar earthquake swarm occurred in 2022 in the nearby West Arthur area. However, the duration of the current swarm and its precise triggers remain unclear.
“Swarms are a bit mysterious, we don’t really know what causes them,” Dr Cummins admitted. “My preferred explanation is that it probably has to do with some kind of production of fluids in the crust, but no-one really knows.”
Enhanced Monitoring for Deeper Understanding
Western Australia is generally more susceptible to earthquakes than other Australian states. However, the current swarm has placed the Great Southern region under a particular spotlight. In response to the ongoing activity, the Geological Survey of Western Australia (GSWA) is deploying additional monitoring equipment to Gnowangerup. The aim is to gain a more comprehensive understanding of the underlying geological processes at play.
Dr John Paul O’Donnell from the GSWA described the swarm as “puzzling.” He noted that while earthquakes do occur within continental plates, making them not entirely unusual in Australia, experiencing them in the middle of the Yilgarn Craton is unexpected. The Yilgarn Craton is recognised as one of Australia’s oldest and most stable geological units, essentially the “engine block” of the continent.
“The stress is being released within the craton, rather than some other geological unit at its margins or boundaries, a younger, weaker unit, and that is something we don’t fully understand,” Dr O’Donnell stated.
He further explained that when “significant” events like this occur, the installation of extra monitoring stations becomes crucial. The data collected from these sensitive instruments will enable the team to pinpoint earthquake epicentres with much greater accuracy, potentially down to a few hundred metres.
“Anecdotally, people are feeling multiple earthquakes a day here, but our devices are ultra-sensitive, so they’ll pick up many, many more, hundreds if not thousands of smaller quakes,” he added.
Despite the increased monitoring, Dr O’Donnell cautioned that it remains impossible to predict whether any larger seismic events might occur. The ongoing swarm continues to be a subject of scientific investigation, with local communities hoping for a return to seismic calm.
