Unpacking Victoria’s earthquake

Map detailing Victoria's earthquake cluster from 22 September 2021

Geoscience Australia have determined that the epicentre of yesterday’s earthquake was near Woods Point, east of Melbourne, at a depth of about 10km.

Early analysis suggests that, at magnitude 5.9, this earthquake is one of the biggest onshore earthquakes ever recorded in Victoria. However, by global standards, it was relatively small.

The ‘main event’ was followed by eight aftershocks. These smaller earthquakes are expected to continue for the coming weeks and months.

Geoscientists believe that that earthquake is probably the result of tectonic plate pressure transferred from New Zealand.

The built-up pressure apparently caused a small segment of an ancient geological fault to be reactivated. Geologists have previously mapped it and named it the Governor Fault.

The Governor Fault is a large, complex structure that extends from near Echuca and the Murray River in the north, to near the Gippsland Lakes in the south. It passes through the heart of the Victorian Alps.

This fault has been considered a prime candidate to be reactivated in the current Victorian stress-field, but it isn’t the only such fault – there are many.

Yesterday’s earthquake was just a continuation of a long, ongoing natural process.

The south-eastern highlands region of Australia regularly experiences small earthquakes, with approximately 60 earthquakes of magnitude 2 and greater over the last 20 years.

The Geological Survey of Victoria has long known about the earthquake potential of our state’s geology and have been undertaking research, together with other interstate and national research agencies to better understand what lies beneath our feet.

If you would like to know more about the Geological Survey of Victoria’s work, and about the effects of earthquakes on the landscape, please view a short film – Geoscience: Beneath the Australian Alps.

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