Waiting for the big one in Australia

Victorian Earthquake small but a reminder

The next Earthquake might be the big one

We do not have much  experience of damaging earthquakes in Australia. This has meant that government and local authority planning  on earthquake risks, is very poor compared with neighbouring regions of ‘higher risk’ such as New Zealand.

A 5.4 magnitude earthquake rocked Victoria mid 2012. The quake did little damage to property and fortunately no injuries were reported. However it should remind us that the earth we live on is not as stable as we might have first thought.

The quake’s epicentre was located 10km southwest of Moe and occurred roughly 10km below the surface. It was the equal-largest earthquake to have occurred in Victoria since the magnitude-5.7 earthquake that occurred near Mount Hotham in 1966.

The public perception of earthquake hazards in Australia tends to be based largely on personal experience.

I remember waking up one morning in Adelaide in the 1970’s with the house shaking. Many of us will have experienced small earthquakes or tremors but for the most part these are located far from built up areas.

Many of you may remember the magnitude-5.6 Newcastle earthquake in 1989. It killed 13 people and left over 100 injured. It caused an estimated AU$1 billion worth of damage. However unless you were directly affected by that event you may think it unlikely to occur in Australia again. However following this event, many property insurers reviewed doing business in Adelaide, the most likely city to one day be hit by an Earthquake.

Our continent is more prone to earthquakes than we might expect. Australia is on a plate thatis drifting north at a rate of 7cm per year. If you drive along the coast, you will see evidence of large seismic events in our geological past. Even near the recent Moe earthquake, the tilting of beach deposits at Warratah Bay suggests multiple, large earthquake events have occurred in the region’s fairly recent past.

Further north, the development of a cliff-like embankment, on the Cadell Fault, has changed the course of the Murray River near Echuca a number of times in the past 100,000 years. These events must have been in the order of magnitude 7 or greater.

In 1897, a significant magnitude-6.5 earthquake occurred on an unnamed fault off the coast of South Australia near Beachport. That earthquake apparently rang church bells as far away as Bendigo.

Active plate boundary earthquakes, such as the Tōhoku-Oki earthquake of March 2011 (which led to the Fukushima nuclear disaster) and the April 2012 earthquake off the coast of the Indonesian province of Aceh are well known to be devastating.

However, the recent earthquake in Moe was what is known as an intra-plate earthquake. This means, it occurred away from an active tectonic plate boundary. Intra-plate earthquakes can be very damaging.

The magnitude-6.3 earthquake that hit Christchurch in February 2011 was about 150km east of the tectonic plate boundary, and was part of a sequence of shallow intra-plate earthquakes. And yet this earthquake killed around 180 people and caused tens of billions of dollars damage. The epicentre of the Christchurch earthquake was characterised by a pattern of high-amplitude, high-frequency and short-duration ‘strong motion’. Strong motion implies that monitoring seismometers were overwhelmed in the event.

This pattern of ‘strong motion’ is typical of that observed in relatively shallow intra-plate Australian earthquakes and hints at what we could expect, should a quake of similar size occur here. With a similar magnitude event occurring, on average, once every five to ten years across Australia, that is not unlikely.

Public and institutional perception of ‘low risk’ is one of the reasons researchers are seeking an improved understanding of Australia’s crustal stability. Our lack of damaging earthquakes in Australia has meant that government and local authority planning  on earthquake risks is very poor compared with neighbouring regions of greater risk, like New Zealand.

New hazard data and maps are currently being developed by a number of research groups to begin the establishment of new planning codes and disaster management strategies that specifically consider seismic hazard.

Emerging new energy technologies, such as geothermal energy, geological carbon storage and unconventional gas,  provide further research directions in terms of crustal stability. These developing technologies typically involve injecting or removing fluids from the earth’s crust. We have already mentioned previously that fracking has been linked to some earthquakes in Europe and America. So a detailed understanding of the risk potential of prospective regions is critical to mitigating against man made caused earthquakes. It also reduces the potential for naturally occurring events to negatively impact public opinion on these types of projects.

The Moe earthquake in Victoria, will remind some of us that Australia is still prone to devastating events.