Earthquake swarm in Gnowangerup as tremors expected for months
earthquake activity in the Great Southern town of Gnowangerup has exceeded 100 events since the start of the year, and seismologists say residents should brace for the sequence to continue for several months.
Earthquake swarm: Where things stand
Geoscience Australia’s senior seismologist Dr Jonathan Bathgate describes the episode in Gnowangerup as an earthquake swarm rather than a classical foreshock–mainshock–aftershock sequence. Public records show more than 100 low-level earthquakes since January, with one 3. 8-magnitude event identified as the largest so far. That 3. 8 event generated large numbers of felt reports in one set of submissions, with some reports coming from more than 50km away in Katanning; other local counts recorded smaller numbers of felt reports. Independent monitoring shows dozens of events in short order: one record lists 31 earthquakes within a single week and notes more than 70 since February.
What is driving the swarm and likely paths?
Dr Bathgate links the activity to regional crustal stress redistributed by broad tectonic motion. The Australian continent’s northward movement redirects stress within crustal rocks, which then concentrates and releases along pre-existing lines of weakness. Clustered swarms have occurred previously in the South West seismic zone, with examples in Burakin, Beacon and Arthur River. Past behaviour in the region includes a magnitude 4. 5–5 event in 2023, and swarms elsewhere have lasted from months up to a couple of years before fading.
On present behaviour, the sequence is dominated by magnitude-two and -three events clustered within roughly a 10km radius, and Dr Bathgate notes that the release of energy through many small events tends to reduce stored stress. While he describes it as unlikely the swarm will produce a damaging earthquake, he emphasizes that the possibility cannot be ruled out.
What residents should expect and how this could play out
Local perspectives mirror the scientific description. Ron Bett, owner of a Gnowangerup fuel business, says small swarms are not unusual for the region and that recent tremors have not been linked to damage, though he recalls a stronger event in the past that forced a household to relocate. For planning and preparedness, the immediate guidance is pragmatic: expect ongoing shaking for months, acknowledge uncertainty about exact duration — swarms have been observed to fade slowly over periods of months to a couple of years — and recognise that most events so far have been small.
Three plausible paths forward, constrained to observations and expert signals, are:
- Best case: The swarm continues with predominantly magnitude-two and -three events and gradually peters out over months, releasing stress through many small quakes.
- Most likely: Continued clusters of small earthquakes for several months, consistent with recent weekly counts and expert expectation that residents should brace for ongoing activity.
- Most challenging: A larger event occurs within the region’s known potential, mirroring the magnitude 4. 5–5 activity documented previously, a possibility experts say cannot be excluded.
Given those paths, winners in the near term are communities with recent preparedness measures and resilient structures; those at greater risk are older buildings already showing damage from past events. Emergency services and local businesses will face demand for advice and practical support if shaking continues or intensifies.
Readers in Gnowangerup and surrounding towns should follow local official guidance, take straightforward preparedness steps for small tremors, and remain aware that the swarm is likely to continue for months as the region experiences this earthquake
