UW professor part of team researching earthquakes in Japan

OLYMPIA, Wash. – To understand why University of Washington professor Harold Tobin went to Japan, all you need to do is look at a map.

“Japan is the most seismically active country in the world. Japan and Indonesia,” he said.

Tobin just came back from a two-month research trip primarily on board a boat off the coast of southern Japan. The team consisted of 170 members, and 25 members of the team are scientists, said Tobin.

The goal, according to Tobin, is to better understand Japan’s earthquake subduction zones.

“The Japan trench in the north is where that 2011 earthquake took place, and then in the south, there’s a second one that we think as the sister subduction zone to Cascadia actually. It’s very similar in many of its plate tectonic characteristics,” said Tobin.

According to Tobin, it’s called the Nankai Trough, which is where he and his team spent most of the time. The project is ambitious.

“Really ambitious. To drill a five-kilometer deep hole, a three-mile deep hole, off shore into the fault,” Tobin said.

The goal is to eventually place seismometers, temperature and pressure sensors and other instruments that detect tilts and strains in the earth's crust, said Tobin.
The crew is about halfway down digging the hole.

"We think that if we get inside the fault zone, or very near to it, we can learn more fundamental things about how these faults actually build up stress and then suddenly break or rupture,” said Tobin.

And that information can hopefully understand the 'Cascadia Subduction Zone' off of Washington's coastline.

“They both generate earthquakes of magnitudes of 8 and 9 or higher and large tsunami’s on a several hundred year interval,” said Tobin.

Both the Nankai and Cascadia have similar geometries and temperature profiles, said Tobin. But if you look at the frequency or how many earthquakes happen between both, that is the eye-opener.

"The ones that we think are sort of locked-and-loaded that aren't showing us a lot of smaller earthquakes, meaning they're just maybe storing up energy toward the bigger ones. Nankai is quiet that way. The quietest one on the planet is actually Cascadia. And we worry about that because it's locked and storing up all of its plate tectonic strain,” Tobin said.

The last earthquake on the Cascadia happened sometime in 1700. Based on geological evidence, it generated between an 8 to 9 magnitude quake.

“When the plate is trying to go down, they get stuck together, and they lock. And it gets pulled down, kind of like an archer pulling a bow string back. It creates this tension and then boom it boosts forward and the subduction slips maybe as much as 100 feet, 200 feet, that's what pushes the water and creates the tsunami,” said Tobin.

And there are shallower faults that run underneath Seattle and Tacoma.

“Those faults seem to have a record of occurring every few thousand years, but could be really damaging because they’re near the surface, the shaking would be more intense proportionately,” he said.

Professor Tobin said it’s very hard to predict when the next quake will hit, which is why there is so much push for technology like eventually building an offshore fiber optic network like in Japan, here in Washington.

That would provide real time earthquake data, but also education and preparedness like shake alerts. The recent Cascadia Rising preparedness drill will help too.

“It could be literally tomorrow, but it could just as easily and just as likely 200 years from now. But understand that on a day-to-day basis the hazard is not that high,” he said.

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