In Search of the Next Big One

Subduction zones are the source of the world’s most dangerous earthquakes and tsunamis. UTIG’s researchers are on a mission to understand them.

By Constantino Panagopulos

On Jan. 26, 1700, a barrage of tsunamis ripped across the Pacific Ocean at the speed of a jet liner. The 100-foot waves slammed into the northwest coast of America and carved a path of destruction 3 miles inland. Hours later, towering waves destroyed coastal villages in Japan, searing the catastrophic event into the cultural memory of people on both sides of the ocean.

The disaster was the result of a magnitude 9 earthquake at the Cascadia fault in the Pacific Northwest, which struck with such violence that the coastline dropped by at least 3 feet.

Cascadia is one of several subduction zones on the Pacific Ring of Fire, an area responsible for many of the world’s largest earthquakes and tsunamis. That’s why it’s a hotspot for Jackson School of Geosciences researchers with the University of Texas Institute for Geophysics (UTIG), one of the foremost investigators of subduction zone earthquake hazards worldwide.

Subduction zone earthquakes are a worldwide problem, but scientists have yet to find a reliable way of forecasting when the next big one will hit.

“They are the only large-scale natural hazard for which we are truly at the mercy of the planet,” said UTIG Director Demian Saffer.

UTIG researchers are investigating subduction zones around the globe in search of insights into how they work.

In Japan, they took the deepest- ever measurement of the country’s Nankai fault and installed a network of subseafloor sensors. In New Zealand, they are wiring up the Hikurangi fault to assess the risk it poses to the country’s east coast. And in the Pacific Northwest, UTIG researchers co-led the first-ever complete subsurface imaging of the Cascadia fault. Other ongoing field investigations include subduction zones off the shores of Chile, Costa Rica, Mexico and Alaska.

Back in Austin, UTIG lab researchers have constructed a scaled-down fault zone for studying earthquakes up close. And now a UTIG-led initiative is working to create the first physics-based earthquake forecasts, a feat that would put scientists’ understanding of earthquakes on the same track as weather and climate predictions.

“We’re bringing every method at our disposal to the table as part of a concerted effort to better understand subduction zone earthquakes and the hazards they pose,” Saffer said.

Wiring Up Faults

Subduction zones are found in the deepest parts of the ocean and stretch for miles under the seafloor. To study them up close, UTIG researchers are using sensor- packed observatories drilled over a thousand feet into the seafloor.

Installing subsurface instruments in the deep ocean is no mean feat, but UTIG researchers have been doing it successfully for over a decade.

In Japan, where the Nankai fault has been eerily quiet for decades, Saffer co-led a series of International Ocean Drilling Program (IODP) expeditions, the last one in 2018, to place a new network of observatories on the seafloor where the fault faces Tokyo.

“The observatories let us hear every tiny creak, even those far out at the trench,” Saffer said. “It puts our finger right on the fault’s pulse.”

Among other details, the observatories revealed previously unknown movement that researchers think lets the fault periodically release some tension and could be important in understanding how it causes tsunamis.

With Japan’s Nankai wired up, Research Scientist Laura Wallace and other UTIG researchers are now leading efforts to do the same at New Zealand’s Hikurangi fault.

Two observatories were installed in 2018 by an IODP expedition led by Wallace. Since then, Wallace returned to the observatories in 2021 and 2023, sending remotely operated vehicles 2 miles down to the seafloor to dock with the observatories and download their data.

The results so far are encouraging and are already factoring into New Zealand’s latest earthquake hazard assessment models.

“We’re seeing where and when strain builds in the Earth’s crust in far greater detail than I ever would have imagined,” Wallace said.

A Geologic Ultrasound

When an undersea earthquake hits in a particular way, it creates a whiplash in the ocean floor that triggers a tsunami. While subduction zone earthquakes are destructive enough on their own, it’s the tsunamis that make them exceptionally dangerous.

To find out which faults have the most potential to cause a tsunami, UTIG scientists are using seismic imaging to peer inside subduction zones and see what makes them tick. They’re finding that what plates are made of plays a big role in the threat they pose.

In 2017, Andrew Gase, a UTIG graduate student researcher, joined an international team of scientists aboard the R/V Marcus Langseth on the longest continuous seismic survey of the Hikurangi fault. For 35 days, the ship sailed along the 300-mile margin, performing an ultrasound of the fault using seismic pulses and a 7-mile-long microphone.

What he found was a fault divided. In the north, where the fault is known to cycle harmlessly through regular slow-motion earthquakes, called slow slip events, he found a motley mixture of rocks of all sizes and origins, including ancient volcanoes and sea sediments.

In the south, however, where measurements show that the fault is stuck, he found a mile-thick homogenous wedge of sand jammed in the fault right where the largest earthquakes are thought to happen.

Now a postdoctoral researcher at Western Washington University, Gase thinks that the motley rocks in the northern section mean the fault breaks more easily, releasing the locked plates before tectonic forces can build. Remnant volcanoes that are being sucked into the fault further roughen the fault and halt the occurrence of large earthquakes. In the south, however, the sandy wedge has made the fault rigid and smooth, which might create resistance with the tectonic plates until they slip all at once and smash together in a large earthquake.

Making Earthquakes

Research Scientist Associate David “Chas” Bolton is gluing dime-size sensors to a squat, car-size metal frame. He’s in a warehouse at The University of Texas at Austin’s J.J. Pickle Research Campus, dwarfed by vats, pipes and large equipment, but the instrument he’s working on is by far the most unusual.

It’s called the Earthquake Machine. The device was designed and constructed by Bolton and Srisharan Shreedharan, a former UTIG postdoctoral researcher, to work like a model subduction zone.

The machine pushes two synthetic tectonic plates together until the fault breaks with a loud snap while sensors record every detail. Although its fault is only a little over 3 feet long, that’s still much larger than most lab-scale faults, which are usually only a few inches in length.

“What’s unique with this machine is that because it’s so large, it’s going to allow the ruptures to nucleate and propagate in ways
that are more analogous to what actually happens along natural fault zones,” Bolton said.

This means that unlike typical lab-scale faults that break all at once, their Earthquake Machine is large enough that earthquakes should break along just parts of the fault.

It also means they can configure it to mimic a divided subduction zone like Hikurangi.

The researchers said it can replicate other kinds of faults such as San Andreas or the complex faults found in the Permian Basin.

It’s one of several large devices at the Jackson School’s GeoMechanics & GeoFluids lab that are designed to simulate faults under the kind of pressure found miles underground.

“Having these instruments under one roof allows us to explore how earthquakes nucleate and evolve in different types of fault rocks, as they might in the real world, and that’s a pretty unique combination,” Saffer said.

Cascadia

For the people living on Japan’s east coast, the tsunami of Jan. 26, 1700, came out of nowhere. The merchants who detailed the destruction wrote of an “orphan” tsunami that arrived with no accompanying earthquake.

The wave, of course, was no orphan. It was set off by a massive earthquake on the other side of the Pacific Ocean, at Cascadia.

For the Native American and First Nations communities who lived there, the event was catastrophic. More than 600 miles of the fault slipped, triggering waves that swept away forests and wiped out entire communities.

Since then, Cascadia’s subduction zone has remained mysteriously quiet. “The question is when the next big one will happen,” said Shuoshuo Han, a UTIG research associate who studies Cascadia.

According to Han, ancient lake deposits and petrified tsunami ripples show that Cascadia produces a near-magnitude-9 earthquake every 300 to 500 years. That means the next one could be on the horizon, yet until recently not much was known about the fault.

That all began to change in 2021 when Han co-led a research cruise aboard the R/V Marcus Langseth to image the entire subduction zone — from Vancouver Island to the northern tip of California — for the first time. The cruise produced spectacular images of the subduction zone, revealing previously unknown details about the geometry and physical properties of the part of the fault responsible for great earthquakes.

“This data set will provide critical information for future computer modeling work on earthquake rupture along the Cascadia subduction zone,” she said. “I think it will greatly advance our understanding of this margin in particular, but also earthquake and tsunami processes at subduction zones in general.”

Getting Serious About Forecasting

Whether it’s observations from state-of-the-art instruments or using big data to pluck clues from archives, UTIG has an impressive record of making break-through discoveries about the world’s major subduction zones. The goal, of course, is to know when the next big earthquake or tsunami is most likely to strike.

That’s where UTIG’s computational modelers come in.

The processes behind earthquakes are, at present, too complex to be useful for predictions. But scientists are hopeful that a new generation of computer models could help them better understand the timing and strength of future earthquakes and even forecast their potential damage.

Among those leading the way is UTIG’s Thorsten Becker, who in 2021 launched a National Science Foundation-funded project to figure out the physics needed to make earthquake forecasting a reality.

“We’ve brought together people with expertise in different parts of the problem to see if we can build a model that captures it all,” said Becker, who is also a professor at the Jackson School’s Department of Earth and Planetary Sciences.

Known as the Megathrust Modeling Framework, the goal is to develop models that glue everything together: earthquake nucleation, seismic cycles, tectonic strain, subducting materials, anything from the gaps between mud grains to the march of continents.

The models will merge and compare findings from three natural laboratories: Japan, New Zealand and Cascadia. The project is already developing computational tools to narrow in on uncertainties that are critical to understanding earthquakes. But Becker believes the surest way to achieve a quantum leap in earthquake science is to expand the community of people who are working on the problem.

In 2022, the project launched an annual summer school that gets graduate students from across the globe working on real-world earthquake hazard problems.

Becker and his collaborators don’t expect to be giving earthquake forecasts any time soon. But with an emerging generation of researchers who are fluent in geophysics and computational geosciences, he’s confident the science and tools to do so are within reach. Saffer agrees that with UTIG researchers continuing to push the frontiers of subduction zone research in everything from deep ocean measurements and large-scale field experiments to computer modeling, they could soon be on the cusp of a major leap forward.

“That’s a strength of UTIG,” Saffer said. “We have a critical mass of researchers with a diverse set of tools in their toolbelts, approaching the problem from a very interdisciplinary point of view. You would be hard-pressed to find that in many other programs.”