The earthquake that rattled Melbourne was among Australia's biggest in half a century, but rock records reveal far mightier onesĮarthquakes are more intense and frequent in plate boundary regions. For instance, there is geological evidence for a possible magnitude 7 earthquake occurring sometime between 70,000 and 25,000 years ago, on the Cadell Fault near the Victorian town of Echuca. Other recent earthquakes include two magnitude 5 quakes: one in 1996 near Mt Baw Baw, and one in 2012 near Moe.īut just because we haven’t seen such a high-magnitude earthquake in our time doesn’t mean they don’t happen. This morning’s earthquake was the largest onshore quake ever recorded in Victoria. And while Australia is not a tectonic plate boundary, it is still quite seismically active. The 2016 Petermann Ranges earthquake in the Northern Territory was a magnitude 6.1 quake. That’s based on an instrumental record going back about 150 years. Australia has an earthquake of magnitude 6 or higher every six to ten years, on average. While some early reports suggested today’s earthquake was the “largest on-land earthquake in Australia since 1997”, this isn’t the case. The Conversation Is this an unusual event? The Conversation’s readers sent in their accounts of the earthquake, which was felt across Melbourne’s suburbs. At a magnitude of 5.8 and a depth of 12km, we don’t expect today’s event to have an associated surface rupture, although it is remotely possible. If it’s deep enough, it’s entirely possible for a quake to happen at a fault that never ruptures the surface - so we can’t see evidence for it. Such displacement is only caused by moderate to large earthquakes relatively close to the surface. What we look for here is displacement at Earth’s surface, formed by movement during previous quakes. Most of the neotectonic faults near today’s earthquake were identified from remote elevation data - and this alone doesn’t reveal information such as when, how big and how often previous earthquakes on these faults occurred. Geoscience Australia hosts a database of what we think might be active faults across Australia, but few of these faults have been studied on the ground. And most of this energy release occurs due to the rupture of weak zones in the crust, called faults. However, earthquakes basically happen for the same reason in Australia as they do in New Zealand: there is a buildup of elastic strain energy in the crust, which eventually needs to be released. Many of Australia’s suspected neotectonic faults (faults which have hosted earthquakes in recent geological times) have not been thoroughly investigated, commonly due to lack of funding and resources for earthquake research. Screenshot/Geoscience AustraliaĪustralia experiences fewer earthquakes than plate boundary regions, such as New Zealand. Geoscience Australia had received 32,409 felt reports as of when this article was published. The earthquake was felt across the region at around 9.15am today.
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