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A low-intensity hum near Vancouver Island may help predict the next killer earthquake

There has not been a major earthquake in the Cascadia subduction zone since 1700. But every year or so, there is a month-long ‘slow slip’ of tectonic plates.

It is well known that, off the coast of Vancouver Island, the massive undersea Juan de Fuca tectonic plate is slowly sliding under the larger North American plate, putting the west coast of Canada at grave risk of a megathrust earthquake and resulting tsunami.

What is lesser known about this process is the massive amount of energy that is unaccounted for, and might be building silently toward catastrophe. Newly published research based on artificial intelligence claims to have found it in a constant, low, background tremor, and, with it, a new way of predicting when the next big one might hit.

There has not been a major earthquake in what is known as the Cascadia subduction zone since about 9 p.m. on Jan. 26, 1700, long before Europeans first landed on Vancouver Island. The event is moderately well known to historians, however, for two reasons.

One is the oral histories and archeological remains of the various First Nations whose villages were swamped by a tsunami. Storytellers began to speak of dwarfs in the mountains who danced around a drum, causing the earth to shake and waters to rise. Others described a sea battle between a thunderbird and a whale that caused “a shaking, jumping up and trembling of the earth beneath, and a rolling up of the great waters,” according to research by Alan McMillan, who studies the archeology and ethnography of Vancouver Island First Nations at Simon Fraser University.

The other reason is that the tsunami also went the other way, westward to Japan, making landfall the next day, killing hundreds and sinking boats.

Ever since, Cascadia has been relatively quiet. But every year or so, there is a roughly month-long “slow slip,” when the North American plate lurches southwesterly over the Juan de Fuca plate.

This slip can account for as much as half of the total relative motion of the tectonic plates, as measured by displacement on the surface. It is usually accompanied by bursts of tremors, but the physics of “slow slip” is not well understood. It only occurs in some regions of the fault line between the plates, for example, while others appear to be “locked,” and only move in megathrust events.

This slip has been observed in advance of major earthquakes, which suggests it might be part of the process that causes them, according to a new paper by Bertrand Rouet-Leduc and Claudia Hulbert of the Los Alamos National Laboratory in New Mexico.

There is also a strange discrepancy between the amount of surface movement as measured by global positioning systems and the amount of energy measured by seismographs in tremors.

Somewhere in this process, a vast amount of energy has gone missing.

The key to finding it was to apply the tools of supervised machine learning, a kind of artificial intelligence that can separate a real signal from background noise. In a newly published paper, the researchers claim to have found that the Cascadia subduction zone is “continuously broadcasting a low-amplitude, tremor-like signal,” and that this low amplitude hum from the depths of the Earth “may account for most of this missing energy.”

Recognizing what this hum reveals about fault line physics might lead to something like an early warning system that “may prove useful in determining if and how a slow slip may couple to or evolve into a major earthquake,” the authors write in the journal Nature Geoscience.

They used seismic data from the Canadian National Seismograph Network and global positioning data from stations in the Western Canada Deformation Array, processed by the United States Geological Survey.

They found the Juan de Fuca plate is moving under the North American plate at around four centimetres a year as the North American plate slips over it. The highest slip speed for the North America plate, moving in the other direction, was also around four centimetres a year, which means that the transition zone between the plates — coastal British Columbia, basically — was slipping at around eight centimetres a year.

“The continuous tremor-like signal we identify tracks the slow slip rate, apparently at all times, and so provides real-time access to the physical state of the slowly slipping portion of the megathrust,” the authors write. “As the slow earthquakes transfer stress to the adjacent locked region where megaquakes originate, careful monitoring of this tremor-like signal may provide new information on the locked zone, with the potential to improve earthquake hazard assessment in Cascadia.”

Source: https://nationalpost.com/news/canada/a-strange-low-intensity-hum-near-vancouver-island-may-help-predict-when-the-next-killer-earthquake-will-strike

Ontario town rattled by ‘mining-related’ earthquake

It wasn’t a particularly strong quake, but it didn’t need to be for Kirkland Lake residents to feel the tremor on Wednesday night [December 12th, 2018] — it happened right underneath their feet.

According to Earthquakes Canada, the magnitude 3.2 earthquake was centred almost directly under the city, 2 km west-southwest of town, at a depth of 1.5 km. More than 100 people reported to Natural Resources Canada that they felt the quake, which struck at 11:16 EST Wednesday night. Weather Network viewers reported hearing a “loud blast that shook a lot of homes” at the time the quake was recorded.

Earthquakes Canada lists the tremor as ‘mining-related’, although no confirmation has been released. Local resident Jeff Wilkinson told CTV News he was concerned it might have been a fracture related to mining. “As you may know,” Wilkinson told CTV, “we have had some fatal rockbursts in this area, so we’re all sort of wondering whether it has happened again.” A rock burst is a sudden, sometimes explosive, fracture that can happen in deep mines. The rock surrounding a mine shaft is under tremendous pressure from the rock surrounding it; sometimes this pressure can cause the rock surrounding the shaft to give way.

DOES MINING CAUSE EARTHQUAKES, OR IS IT THE OTHER WAY AROUND? 

There has definitely been a lot of coverage of fracking-related earthquakes in recent years, as geologists point to the oil-extraction process for the rising number of quakes in places like Ohio and Oklahoma. Earthquakes related to mineral mining are a slightly different animal, however.

As happens with rock bursts, since mining leaves empty spaces that change the balance of pressure on the surrounding rocks, it’s not unusually to get minor earthquakes related to the collapse of excavated regions. The excavation process itself can also result in events that register on the seismometer. According to a report from the Canadian Hazards Information Service, “Literally hundreds of [mining-induced activity] blasts are recorded and identified by the project on a yearly basis.”

Sometimes it’s a case of ‘the chicken and the egg’, however.

A lot of the minerals that people mine for are actually largely found along fault lines — gold being among them. As Daniel Jaska, of the Geoscience Australia Earthquake Alert Centre, put it talking to ABC, “we have mining because of earthquakes.”

“[Minerals like gold] are [along faults] because when and earthquake occurs, there is generally a flow of water or liquid that interacts with the rocks,” said Jaska, “and over many millions of years forms minerals.”

While seismic activity in central Canada tends to be fairly low, thanks to a lake of tectonic plate interactions in the area, there are ‘weak zones’ within plates that are subject to shifting when stress builds up in the interior of a plate, thanks to constant pushing at its edges.

Source: https://www.theweathernetwork.com/news/articles/earthquake-felt-in-kirkland-lake-officials-believe-mining-related-gold-mine-mining-seismicity-rockburst/119806

Powerful quakes buckle Alaska roads, briefly trigger tsunami warning

Back-to-back earthquakes measuring 7.0 and 5.8 rocked buildings and shattered roads Friday morning, November 30, 2018 in Anchorage, Alaska, sending people running into the streets and briefly triggering a warning to residents in Kodiak to flee to higher ground for fear of a tsunami.

The warning was lifted a short time later. There were no immediate reports of any deaths or serious injuries.

The U.S. Geological Survey said the first and more powerful quake was centred about 12 kilometres north of Anchorage, Alaska’s largest city, with a population of about 300,000. People ran from their offices or took cover under desks.

Cracks could be seen in a two-story downtown Anchorage building, and photographs posted to social media showed fractured roads and collapsed ceiling tiles at an Anchorage high school. One image showed a car stranded on an island of pavement, surrounded by cavernous cracks where the earthquake split the road.

Cereal boxes and packages of batteries littered the floor of a grocery store, and picture frames and mirrors were knocked from living room walls.

People went back inside after the first earthquake struck, but the 5.8 aftershock about five minutes later sent them running back into the streets.

A tsunami warning was issued for the southern Alaska coastal areas of Cook’s Inlet and part of the Kenai peninsula. Kodiak police on Kodiak Island warned people in the city of 6,100 to “evacuate to higher ground immediately.”

The National Weather Service Seattle tweeted a tsunami warning is in effect for Cook Inlet, but it is not expected to affect Washington or B.C.

Anchorage lawyer Hank Graper was driving when the quake struck. He first thought his vehicle had a flat tire, then thought it was exploding. He realized it was an earthquake after he saw traffic poles swaying.

Graper called it the most violent earthquake he’s experience in his 20 years in Anchorage.

David Harper was getting some coffee at a store when the low rumble began and intensified into something that sounded “like the building was just going to fall apart.” Harper ran to the exit with other patrons.

“The main thought that was going through my head as I was trying to get out the door was, ‘I want this to stop,”‘ he said.

Harper said the quake was “significant enough that the people who were outside were actively hugging each other. You could tell that it was a bad one.”

Thrown from bathtub

In Kenai, north of Anchorage, Brandon Slaton was alone at home and soaking in the bathtub when the earthquake struck. Slaton, who weighs 209 pounds, said it created a powerful back-and-forth sloshing in the bath, and before he knew it, he was thrown out of the tub by the waves.

His 55-kilogram mastiff panicked and tried to run down the stairs, but the house was swaying back and forth so much that she was thrown off her feet and into a wall and tumbled to the base of the stairs.

“It was anarchy. There’s no pictures left on the walls, there’s no power, there’s no fish tank left. Everything that’s not tied down is broke,” Slaton said.

Slaton ran into his son’s room after the shaking stopped and found his fish tank shattered and the fish on the closet floor, gasping for breath.

He grabbed the Betta fish and put it in another bowl. He says the area was eerily quiet. His children’s school was evacuated.

Alaska averages 40,000 earthquakes per year, with more large quakes than the other 49 states combined. Southern Alaska has a high risk of earthquakes due to tectonic plates sliding past each other under the region.

According to the U.S. Geological Survey, the Pacific plate is sliding northwestward and plunges beneath the North American plate in southern Alaska, the Alaska Peninsula and the Aleutian Islands.

On March 27, 1964, Alaska was hit by a magnitude 9.2 earthquake, the strongest recorded in U.S. history, centred about 120 kilometres east of Anchorage. The quake and the tsunami it triggered claimed about 130 lives.

Source: https://www.cbc.ca/news/canada/north/earthquake-anchorage-1.4927624

Earthquake near Fort St. John ‘very likely’ caused by fracking

An earthquake that struck northeastern B.C. on Thursday evening was “very likely” caused by fracking, a preliminary investigation has found.

Earthquakes Canada said the quake had a preliminary magnitude of 4.5, with the epicentre about 16 kilometres southwest of Fort St. John.

It hit around 5 p.m. PT, followed by another tremor of similar magnitude, classified as an aftershock, less than an hour later.

The Geological Survey of Canada and the B.C. Oil and Gas Commission launched an investigation to figure out what caused the tremor.

On Friday, a statement said they had confirmed there was active fracking happening near the epicentre when the quake struck.

“The likelihood this was induced … there’s a very high correlation,” said Honn Kao, seismology research scientist with the Geological Survey of Canada.

Kao stressed the link was a preliminary finding and more investigation is required before the agency confirms the quake was “100 per cent” a result of fracking — but said it’s “very likely” that’s the case.

Hydraulic fracturing — or fracking — is the process of injecting water, sand and other chemicals underground at a very high pressure to fracture shale rock, in order to extract natural gas.

Western Alberta and northeast B.C. have a high rate of fracking-induced earthquakes, according to a study from the University of Alberta.

Tremor ‘lightly felt’

People in Fort St. John, as well as Taylor, Chetwynd and Dawson Creek, reported feeling the earthquake on social media, but there are currently no reports of damage.

Kao said early data suggests the quake had a relatively shallow depth, which is likely why the quake was widely felt.

“This is certainly an event that has been felt quite a bit by the local residents,” Kao said. “Although this is a significant event for the region, I don’t think it’s going to cause significant damage.”

According to the U.S. Geological Survey, the quake had a preliminary magnitude of 4.2.

Source: https://www.cbc.ca/news/canada/british-columbia/earthquake-fort-st-john-fracking-1.4927898

4.2-magnitude earthquake strikes near Fort St. John

An earthquake struck an area in northeastern B.C. close to Fort St. John on Thursday, November 29, 2018 after 5 p.m. PT.

According to the U.S. Geological Survey, the quake had a preliminary magnitude of 4.2 and the epicentre was 22.4 kilometres southeast of Fort St. John.

People in Fort St. John, as well as Taylor, Chetwynd and Dawson Creek reported feeling the earthquake on social media, but there are currently no reports of damage.

Honn Kao, a research scientist with the Geological Survey of Canada, said early data suggests the quake had a relatively shallow depth which is likely why the quake was widely felt.

“This is certainly an event that has been felt quite a bit by the local residents,” Kao said. “Although this is a significant event for the region I don’t think it’s going to cause significant damage.”

Hydraulic fracturing in the area

Although it is unconfirmed what caused this earthquake, Kao said the B.C. Oil and Gas Commission is investigating if the quake is related to hydraulic fracturing operations in the area.

Hydraulic fracturing — or fracking — is when water, sand and other chemicals are injected underground at a very high pressure to fracture shale rock deep underground in order to extract natural gas.

“They will have to link the location and time of this event to the injection operations nearby,” Kao said.

This area of the country — western Alberta and northeast B.C. — has a high rate of fracking-induced earthquakes, according to a study from the University of Alberta.

Source: https://www.cbc.ca/news/canada/british-columbia/4-2-magnitude-earthquake-strikes-near-fort-st-john-1.4926772

Another earthquake in B.C., breaking down this latest rumble

Another earthquake was measured west of Vancouver Island on October 31st, just shy of a magnitude 5.0 on the Richter scale. Is it another earthquake related to the more powerful episodes back in October?

How many earthquakes do you think have occurred in British Columbia over the past month? 10? 20? 50? We’ve entered quite a tectonically active period.

When reviewing the data, over 80 earthquakes have been measured by sensitive seismometers, but only a couple have been felt. That’s the reality of the plate tectonics around British Columbia, with major plate boundaries being offshore.

The earthquake on the evening of October 31st is a distant cousin of the recent uptick in earthquake activity along a specific fault line, not associated with the Cascadia subduction zone. This was likely an aftershock on the series of greater than magnitude 6.0 earthquakes located on the Sovanco fault. This specific transform fault boundary moves by plates sliding in opposite directions. In this case, the motion is related to the movement of the Explorer and Pacific plates.

DO WE WORRY?

No. But, The ‘big one’ may happen 5 minutes from now, 5 years, or it could be well over 100 years away. From a preparedness standpoint, expecting the earthquake sooner, rather than later will ensure we’re ready to act when the inevitable big shake occurs. A mega-thrust earthquake is one that features a disastrous magnitude 9.0 or greater energy release, but another likely scenario is a weaker, more shallow earthquake under Vancouver Island, or even the Lower Mainland.

For more please refer to the following link (which includes excellent video breakdowns of the tectonic plates movement):

Source: https://www.theweathernetwork.com/news/articles/earthquake-british-columbia-aftershock-vancouver-island-powerful-earthquake-october-vancouver/116148

Several earthquakes strike off Vancouver Island, with no reports of damage

A series of three large earthquakes have struck off the coast of British Columbia, according to the United States Geological Survey.

There were no immediate reports of casualties or damage from the quakes.

The first struck just before 11 p.m. PT Sunday, around 190 km southwest of Port Hardy, a town on the northeast end of Vancouver Island.

The first quake, reported as a magnitude 6.5, was followed by another, with a magnitude of 6.8, around 40 minutes later.

The third quake was reported at magnitude 6.5 just before midnight, near the same area as the previous two.

Three in a row ‘unusual’

CBC meteorologist and seismologist Johanna Wagstaffe said the earthquakes are a reminder that B.C. is in a “complicated” tectonic setting.

British Columbia is located on the Pacific Ring of Fire, an active seismic zone where thousands of mostly small earthquakes are recorded annually by sensors in the province.

Most of the quakes happen near the Cascadia subduction zone, an area where the Juan de Fuca and North American tectonic plates converge, stretching from Vancouver Island to northern California.

“If any one of these quakes had hit closer to land, there would have been devastating consequences,” said Wagstaffe about the Sunday-Monday quakes.

“Three large ones in a row does seem unusual, and I’m sure scientists will be learning as much as they can over the next couple of days about the change in stresses just off our coast.”

There were no immediate tsunami warnings following the earthquakes.

Earthquakes Canada also reported a magnitude 4.4 aftershock from the first quake before midnight, and three below magnitude 5.0 early Monday.

Source: https://www.cbc.ca/news/canada/british-columbia/bc-earthquakes-1.4872470

New findings clarify the seismic risk in the Pacific Northwest

How bad would a Cascadia Subduction Zone earthquake be for the Pacific Northwest?

In the last month, several studies were published which not only showcase the dangers posed by this 1,000 km-long (600 mi) plate boundary, but highlight where ruptures may be most likely. The findings show that in the cities of Portland and Seattle, the quake could leave hundreds of thousands of properties damaged and destroyed, and that in places like Seattle, which lies in a sediment-filled basin, shaking could be much more severe.

Three years ago, Kathryn Schultz’ Pulitzer Prize-winning New Yorker essay, The Really Big One, thrust the Cascadia Subduction Zone into the public spotlight. While the convergent plate boundary, which extends from Vancouver Island at its north end to California’s Cape Mendocino at the south, had been known to scientists for decades, the article renewed public interest and scientific focus.

Major population centers exposed to significant risk

The two largest cities in the Pacific Northwest, Seattle and Portland, are home to several million people. In the event of a M=9 earthquake, which is what Cascadia is capable of, the impact would be severe. Part of this is due to proximity to the plate boundary to theses urban centers, but also the geology.

The city of Seattle, the nation’s fastest-growing city, lies in the Puget lowland on the shores of Puget Sound and Lake Washington. While the location creates an ideal trade gateway, it also means the city lies atop a deep basin. This has startling consequences for shaking, according to a recent study by scientists at the University of Washington, the USGS, and University of Southern California. They looked at how buildings ranging from 4-40 stories high would sway (engineers call this “drift”) in simulated earthquakes, comparing the ride in the Seattle basin, and outside it. They found that within the basin, buildings swayed at least three times more than outside of it because of stronger, slower shaking. Thus could result in much greater levels of damage throughout the city, and longer recovery times.

In Portland, 233 km (145 mi) south of Seattle, the situation is not much better. The Oregon Department of Geology and Mineral Industries (DOGAMI) recently published an updated scenario of what a M=9 Cascadia event could do to the city. By assessing the shaking throughout the metropolitan area, they found approximately 38-39% (235,000) of the city’s buildings would suffer some level of damage. This emphasizes, is that in the event of a Cascadia event, the impacts will not only be extremely severe, but extremely widespread.

Where is a great rupture most likely to happen?

While scientists do not know where a rupture will strike, there are clues that point to areas which may be more susceptible. Two of these are ‘locking,’ and seismic ‘tremor.’ As tectonic plates move against one another, stress builds up. Eventually, the stress reaches a critical level, the fault leaps forward and an earthquake takes place. Where plates are “locked,” the amount of stress that can be built up is greatest. Therefore, identifying the most locked portions of the Cascadia Subduction Zone sheds light on areas of greatest risk. The figure below shows that along the plate boundary, locking is greatest in Washington on the one hand, and Southern Oregon and Northern California on the other. Northern Oregon shows quite a bit.

Seismic tremor, which accompanies slow slip events, is common along parts of the Cascadia subduction zones. Tremor seems to be another indication that the fault is locked above a certain depth, but is firing off in very small shocks and slippage just below that depth.

In fact, over the last two weeks, tremor has picked up in Northern Washington, Southern Oregon, and Northern California, as the map from the Pacific Northwest Seismic Network below shows.

Slow slip events are not like regular earthquakes, which last for tens of seconds, but instead last for days to weeks. These events locate just below the locked portions of the fault, and are accompanied high frequency vibration or ‘tremor.’

While scientists are still unsure if periods of intense tremor, such as has occurred for the past two weeks, can presage large earthquakes, strongly-locked tectonic plates tend to produce the largest and most frequent megaquakes. And, a recent study by University of Oregon and University of New Mexico scientists shows that the higher levels of locking and tremor in certain parts of the Pacific Northwest are likely permanent features.

What does this mean for the Pacific Northwest?

Seattle, Portland, and Vancouver B.C. all lie within the zones of elevated tremor and strong locking. In contrast, Eugene lies inland of the portion of the megathrust that is not strongly locked and that produces less tremor. Therefore, the new evidence only confirms and highlights the risk for Vancouver, Seattle, and Portland, and perhaps reduces it for Eugene.

Source: http://temblor.net/earthquake-insights/new-findings-clarify-the-seismic-risk-in-the-pacific-northwest-7443/