Why does Australia have earthquakes? The whole continent is under stress from distant forces
Last Saturday at 9:49am local time, a magnitude 5.6 earthquake occurred about 50km west of Gympie in Queensland. The earthquake was experienced as strong shaking locally, but did not produce any significant damage, likely ...
However, the quake was felt far and wide and small aftershocks continue. More than 24,000 people across eastern Australia reported it, not only in the nearest big city (Brisbane) but as far away as Cairns and Sydney. This was the largest earthquake in onshore southeast Queensland since 1935, when an earthquake of magnitude 5.5 occurred near Gayndah.
Most of the world's earthquake hotspots are near the boundaries between tectonic plates—places such as New Zealand, Japan and Indonesia. Here, earthquakes are frequent because of the immense forces where two plates collide or slide past one another.
But Australia sits in the middle of the Australian tectonic plate, far from any plate edges. So why do earthquakes still happen here?
Tectonically 'quiet'—but not silent
Australia is often seen as tectonically "quiet" and stable.
On average, Australia has an earthquake larger than magnitude 6.0 about once every seven years, and one greater than magnitude 5.0 roughly once a year. Geological studies of recent faults tell us that Australia could host an earthquake up to around magnitude 7.5.