Flat plates – great for eating your dinner off, less good if you want to lessen the risk of a mega earthquake. Yes, we’re being frivolous with our definition of plates here but a new study has discovered a link between the curvature of a tectonic plate and the likelihood of causing an earthquake with a magnitude of 8.5 and above, known as a mega earthquake.
Earthquakes happen when the top layers of the Earth’s crust, known as tectonic plates, press against each other or collide, causing the ground to shake and occasionally shear or part, causing huge waves of energy to flow across the Earth. This can be devastating for built-up areas nearby and can cause tsunamis when it happens at sea.
It was previously believed that mega earthquakes could only occur between the boundaries of young, fast moving plates, until the Indonesian quake of 2004 and the quake in Japan 2011 disproved this theory, recording quakes of 9.4 and 9.0 respectively. The new study by researchers at the University of Oregon, published in Science, suggests that instead, it is the curvature of the tectonic plate that limits the maximum strength of an earthquake.
Geologists currently believe that the reason certain fault lines create such large scale quakes is because they are better at resisting failure, so when they do eventually crack under the pressure the effect is significantly larger.
“The reason they resist failure longer is often debated,” says lead author Quentin Bletery. “I thought variations in fault geometry could be responsible, so I looked for changes in the slope of the major subduction faults of the world.”
Studying the curvature of the plate along the main faults and comparing it with historical data, Bletery was surprised to find that mega earthquakes occurred when the slope was at its flattest, the opposite of what he had previously expected.
The team also found that when the plate has non-heterogeneous sections, so flat areas broken up by, lets say, lumpy bits, the potential size of the quake lessens. Unfortunately, that means huge, flat fault lines, such as the 1,000km-long Cascadia fault across the western coastline of North America, could cause a huge quake if they ruptures completely. This is what happened in Sumatra 2004, when the quake caused a 1,600km rupture.
So if you’re sitting on bumpy plate are you free from the worry of a mega quake? Probably so – the researchers discovered a 99 per cent link between the curvature of the plate and chance of a mega earthquake eruption. Although don’t relax just yet, much weaker quakes can still cause huge amounts of damage.
“The next step in the research is asking why having a flat plate is more amenable to a large earthquake than a curvy plate,” says co-author Amanda Thomas. “The information eventually could lead to improved hazard maps for earthquake-prone areas around the world.”