by COPALIS BEACH, WASH. — When Japan issued its first ever “megaquake” warning last week, Harold Tobin, a seismologist in Washington state, was watching carefully.
The advisory came after a magnitude 7.1 earthquake hit the southern island of Kyushu. Although the quake did little major damage – the largest tsunami wave it produced rose up to your knees – that was not the biggest concern.
Rather, the seismologists worried that the quake would create the stress that could trigger a bomb ticking off the coast: Japan’s Nankai Trough, arguably the country’s most dangerous fault. The subduction zone has the potential to generate tsunami waves 100 feet high and kill nearly a third of a million people, according to Japanese government estimates.
Did the smaller tremor mean the “big one” was on the doorstep? No one could say for sure, but the odds were suddenly higher – if only by a few percentage points.
“Exactly what could keep me up at night,” Tobin said, if it was happening on the West Coast of the US.
In Japan, the council encouraged officials to close beaches, cancel fireworks celebrations and slow trains. People rushed to stock up on emergency supplies.
In the United States, Tobin said, “we don’t have such a protocol.”
However, we have an equally dangerous fault: the Cascadia subduction zone.
A magnitude-9.0 earthquake on the Cascadia fault and resulting tsunami would kill about 14,000 people in Oregon and Washington, according to the Federal Emergency Management Agency.
But if a smaller earthquake like the one Japan saw happened right next to Cascadia, seismologists would have to decide on the fly whether and how to notify the public.
That’s the scenario Tobin has been thinking about for years: If he gets hints that a devastating earthquake is more likely, even just a little bit, what’s the point of sounding the alarm? If the odds say you’d cry wolf — should you?
“You don’t want mass evacuations that aren’t warranted, but you do want people to not go their leisurely ways,” Tobin said.
His quandary is, in part, the result of these strange times in Tobin’s field: Researchers think they’re coming up on triggers or precursors to earthquakes in the world’s most dangerous seismic regions, but the science is far from complete. fixed. And even when the probability of an earthquake may be higher, the chances are still small. This raises big questions about when to issue a warning.
On a cold summer day in Washington state, Tobin and a dozen other scientists hiked up the Copalis River to a cemetery of cedar trees that had been killed 324 years ago.
A kingfisher trembled and the wind shivered through tall, golden grass. It is a peaceful place about a mile from the shore of the Pacific Ocean that tells the story of a violent day.
On January 26, 1700, due to an earthquake on the Cascadia fault the forest went to lurch down more than 3 feet. Soon after, a tsunami perhaps 100 feet high barreled through at 20 or 30 mph.
The scientists were visiting the forest to see the geological evidence of the Cascadia quake first hand. From time to time, they would jump out of their canoes, dig through the mud and pull out a 300-year-old pine cone as evidence.
Experts know that the earthquake was at least magnitude-8.7, so how powerful it was to send the wave around the world that was documented in Japan.
“Some of the best written records of our tsunami in 1700 are from Nankai,” said Brian Atwater, USGS geologist emeritus who led the canoe flotilla. Atwater used those Japanese records, as well as plants buried in tsunami deposited sand and dates from cedar tree rings in Washington, to piece together the story of that tsunami.
Research by USGS geophysicist Danny Brothers shows that at least 30 major earthquakes have likely occurred in the past 14,200 years in parts of the Cascadia subduction zone, which stretches along the US West Coast from Northern California to northern Vancouver Island. A major earthquake can be expected at least once every 450-500 years, on average.
But for years, Cascadia has remained quiet; some scientists say that’s because a lot of it is “locked up” and building stress. When it cuts, a chunk of the sea floor will go forward – perhaps several feet or more. The vertical displacement of the seabed will cause a tsunami to move towards the shore.
“It will be the worst natural disaster in our country’s history,” said Robert Ezelle, director of Washington state’s emergency management division.
For seismologists, the main question now is how to predict this violence in the future. Fast-developing research suggests that faults like Cascadia and Nankai may send out warning signals: a smaller tremor as a premonition, or a subtle rumble that can only be detected by sensors, what scientists call a slip event slow.
In Tobin’s nightmare, the Cascadia fault suddenly emits that kind of groan. Then – what to do?
If a major quake struck off Cascadia, more than 100,000 people would be injured, according to projections – assuming an earthquake strikes when there aren’t many people on the beach. The shaking would last five minutes. The waves of the Tsunami would affect the coast for 10 hours.
Inland hills would liquefy, taking out roads and bridges. About 620,000 buildings would be critically damaged or reduced, including about 100 hospitals and 2,000 schools.
“We’re unprepared,” Ezelle said bluntly.
Washington state advises residents that they will likely have to brace themselves and the elements for the next two weeks.
“It’s going to be neighbors taking care of neighbors,” Ezelle said.
A map of the Pacific Ring of Fire – where tectonic plates meet to create subduction zones and volcanoes – makes Ezelle very uncomfortable.
“In the last 50 to 60 years, and you’ll see that every fault in the subduction zone has ruptured – with the exception of Cascadia,” he said.
Japan lifted its “megaquake” advisory on Thursday, after no unusual activity was detected in the Nankai trough.
In a similar situation in New Zealand in 2016, things played out a little differently.
That November, a magnitude-7.8 Kaikoura earthquake struck the eastern side of New Zealand’s South Island, killing two people and causing more than a billion dollars in damage.
The next day, scientists noticed a few centimeters of movement near the shore of the North Island through satellite monitoring. Subtle vibrations were emanating from the Hikurangi Rim, a subduction zone and the country’s largest fault, which is just below the capital city of Wellington.
It was a slow-slip earthquake, the slowness of the seismic world, that shook Kaikoura. Such quakes release their energy slowly over weeks or months and do not cause any perceptible shaking. Scientists first recognized their existence about two decades ago, thanks to advances in GPS technology.
Some scientists, like Tobin and geophysicist Laura Wallace, think that these slow slip events may precede large earthquakes in subduction zones. Scientists recorded a slow slip event in 2011 before the magnitude-9 Tohoku earthquake and tsunami in Japan, which killed more than 18,000 people and triggered the Fukushima nuclear disaster. A similar pattern played out in 2014, before the magnitude-8.1 earthquake in Chile.
Wallace, who was working for the New Zealand research institute GNS Science at the time of the 2016 quake, spent her waking hours scrambling to track every move, model risk and questions from the government.
“I don’t think I’ve ever felt such a huge burden of responsibility,” Wallace said. “I was taking my dog with me to the office because if we had a big earthquake, I didn’t want to be separated from my dog.”
Wallace and her colleagues found that the probability of a major earthquake had increased by as much as 18 times, and that the risk within a year was between 0.6% and 7%. But the big one did not materialize.
“Which one of these slow slip events will essentially trigger the next one?” Wallace said. “It’s one of the most important problems we’re trying to understand.”
For the Cascadia subduction zone, better understanding of the warning signs requires more data on slow slip events, improved mapping of the fault zone and improved ability to monitor seafloor faults.
Tobin was part of a team that recently mapped the Cascadia subduction zone in even greater detail. They discovered that the fault is separated into four parts, which could all rupture at the same time or individually. The individual parts are capable of producing a magnitude-8 earthquake or higher.
Meanwhile, researchers are trying to strengthen the offshore monitoring network for Cascadia.
Japan has a sophisticated array of seafloor sensors, but is “one of the few places that has those instruments,” said David Schmidt, a geophysicist at the University of Washington.
The United States lags behind in seabed monitoring, but Schmidt and Tobin are part of a group that received $10.6 million in federal funding to add seismic sensors and seabed pressure gauges to a fiber-optic cable off the Oregon coast.
The devices will help keep tabs on Cascadia. If the data can help researchers learn about what’s normal for the defect, they may also be able to determine when it’s time to worry.
This article was originally published on NBCNews.com
