Dive deep into earthquake prediction

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Scientists who study the world’s most dangerous earthquakes are racing against time to get up close and personal with their sources.

The need is urgent: These super-hazardous fault lines are in subduction zones such as the ones that caused the devastating tsunami in Indonesia in 2004 and Japan in 2011. They threaten coastal communities around the world with earthquakes of up to 9.5 magnitude.

“It’s really the biggest risk in terms of loss of life,” says Laura Wallace, a research scientist at the University of Texas Geophysics Institute (UTIG) in the US.

“It really is the biggest risk in terms of loss of life.”

Laura Wallace, University of Texas

There is only one problem. These fault lines tend to occur at the bottom of sea trenches, thousands of meters below the ocean surface, where plates collide and the relatively light rocks of the continents slide slowly across the denser seafloor rock, forcing them down into the Earth’s mantle.

For generations, this process and the resulting earthquakes have been studied by means of land-based seismic networks or, more recently, high-resolution GPS stations that can monitor crustal movements with millimeter-level precision.

But you can’t tell the nuances of how these processes work from a distance, because seismic details are muffled by 100 kilometers or more of interfering rock.

The street was damaged by a 6.6-magnitude earthquake in Hokkaido, Japan, in 2018. Credit: Jiji Press / AFP via Getty Images.

If a fault causes a real earthquake, the wild tools won’t miss it. But much of the work takes the form of gradual motions, called slow slip events, in which the fault moves steadily over days, weeks, or months, rather than the kind of short churches that generate earthquakes.

Slow slip events do not pose any immediate threat, which is really a good thing because they indicate that the bug has not been locked. Instead, the strain is released gradually before it builds up to dangerous levels.

But, Wallace says, reducing stress in an area may simply transfer it to a nearby area. “It’s a double-edged sword,” she says. “A lower risk in one area may increase the risk in another.”

You cannot tell the nuances of how these processes work from a distance.

She says that to really follow this process, it is necessary to go overboard. Unfortunately, this is not cheap.

The tools themselves aren’t very expensive: a few hundred thousand dollars per site, says UTIG Director, Damien Saver. But it cannot be placed on the sea floor and left there. They must be installed in wells that penetrate hundreds of meters into the rocks below.

Going to this depth is important for two reasons, he says: “First, it keeps us away from surface noise from ocean currents. It is more attached to the rock itself, so it is more sensitive.”

Map of the well and ocean floor sensors along the Nankai Trench off the coast of Japan. Credit: JAMSTEC.

It does not mean that the tools themselves are at the bottom of the well. Instead, it is positioned at the top, where it can be maintained, when necessary, by remotely operated submarines. From there, they measured minute pressure changes made from the base of the well—changes that show how fluids are affected in the pore space between the grains of the bedrock as the rocks are slowly compressed, tense, or deformed by tectonic forces.

“It’s extraordinary, the sensitivity we can achieve,” he says. “This allows us to monitor tectonic movements in a really important place with a really unprecedented accuracy.”

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“It’s an extraordinary, delicacy that we can achieve.”

Damien Sapphire, University of Texas

The real cost is drilling wells.

This requires about $16 million to $20 million per hole, plus two months out at sea. “Eight weeks on a boat without vegetables,” Sapphire joked — although it’s clear to an oceanographer, that’s not really a problem.

“It’s really fun,” Wallace says.

So far, drilling networks have been installed in two subduction zones, one near Japan and one in New Zealand – two countries that are earthquake-aware and have the financial capacity to support such research.

Map showing the location of the Hikurangi subduction zone off Aotearoa, New Zealand. Credit: University of Texas Jackson School of Earth Sciences/Google.

The network is located in Japan south of its main island, monitoring a subduction zone directly threatening Tokyo, among other places.

One is located in New Zealand near the Hikurangi Trench along the east coast of the North Island. Widely regarded as the most dangerous seismic and tsunami hazard in New Zealand, this trench was the site of a 7.1-magnitude earthquake in 1947 that caused an 8- to 10-meter tsunami.

Japanese drilling tools are connected to the shore via fiber-optic cables that allow for real-time data monitoring. New Zealand has not yet prepared its seafloor to this level, and its data must be obtained by autonomous submarine vehicles that periodically visit wells, anchor with their seabed instruments, and download the data to return to land.

For now, the difference in data return speed doesn’t really matter, as scientists are still studying it for correlations – something that requires a lot of patience.

But already, interesting insights are emerging. Saver says that in 2015 the Japanese study site was able to observe a slow-slip event that lasted for three months — and was followed shortly after by a 7.0-magnitude earthquake offshore from the Ryukyu Islands, hundreds of kilometers away.

The Japanese study site was able to observe a slow slip event that lasted for three months – and was followed shortly after by a 7.0-magnitude earthquake.

New Zealand tools haven’t been in operation for long – only since 2018 – so they haven’t yet had a chance to link slow slip events at their well sites to larger earthquakes elsewhere. But this does not mean that they do not display important data. “There are things we haven’t seen before,” Wallace says — noting how the 2019 slow-slip event, which occurs in three phases along different parts of the fault, could have been monitored over the course of about two months.

“We see squeaks and groans very close to these events,” she says.

A highway in Aotearoa, New Zealand damaged by a major earthquake in 2016. Credit: Marty Melville / AFP via Getty Images

Ultimately, Wallace and Saver says, the goal is to learn how slow-slip events relate to changes in large earthquake hazards. “I don’t think we’ll ever be able to predict earthquakes, but doing a better job of forecasting is definitely, I think, on the horizon,” Wallace says. The distinction, she adds, is the difference between making a definitive forecast (an earthquake with a magnitude “x” at this point will happen at such and such time, for example) and assessing probability — similar to a weather report that suggests a 30% chance of rain.

However, such predictions are only possible for subduction zones where the instruments are installed – and only then if they are connected to fiber-optic cables that can return data in real time.

Savir says proposals are already under consideration for the Pacific Northwest of the United States, and another for southern Japan. But the goal is clear. “Every subduction zone in the world should have these kinds of tools,” he says.

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