You’ve probably heard of the Juan de Fuca plate: either as a relatively small oceanic plate that’s being pushed and pulled underneath the North American continent … or as what will cause the Doomsday Earthquake. In any case, that little plate causes the earthquakes and the volcanoes and makes the Pacific Northwest one of the most interesting places on the planet, geologically speaking.
But even with the cornucopia of knowledge geologists have about our coast, they’re still lacking in some of the mechanics of it all.
Until now.
Haiyang Gao, a doctoral student from China, arrived in America 10 years ago, at the height of a geological breakthrough.
In the early 2000s, Japanese scientists had been detecting a discrepancy in the way the Juan de Fuca plate moves. The long-term trend is that the plate is moving northeast. But some geodetic instruments (which record the horizontal and vertical movement of the ground) along the Cascadia Subduction Zone (from Vancouver Island to Northern California) have recorded that every 10-14 months, the plate briefly moves in the opposite direction — to the southwest.
“(At first) they thought it was just noise,” Gao said. “But for some stations, they recorded very consistent results. This motivated people in the Cascades to take a closer look.”
The opposite movement, called a “slow slippage event,” happens very regularly, giving scientists an incredible opportunity to investigate and learn more about how the fault works. The event lasts two-four weeks, and during this time, seismometers on the surface detect tremors that propagate along the fault line. The reason geologists call this a “slow earthquake” is because of traveling.
The event may happen in one place, and days later, a seismometer hundreds of miles away detects a tremor because the plate moved.
You’re probably thinking, “So why do we care?”
This may not seem that exciting to a non-geologist, but trust me, we care because we have this threat of a giant, coast-shattering earthquake that could happen in the near future, which will most likely be caused by the Juan de Fuca plate.
Geologists are doing all they can to investigate how the Juan de Fuca plate is related to these massive events.
Unfortunately, this part of the world doesn’t have the kinds of earthquake records or experiences other more earthquake-frequented parts of the world have, such as Japan, so our tools to study earthquakes aren’t as sophisticated.
We do have some records, and it seems that the massive earthquake happens every 300-500 years, with the last one occurring in the 1700s.
We know how the earthquakes happen — rocks along the fault interface (where the subducting plate meets the continental plate) build up energy as they’re being compressed in what is called the “lock zone.”
As subduction, or the movement of a tectonic plate underneath another, proceeds, more pressure is being put on these rocks, and eventually they snap like twigs in the “free slipping zone,” letting out all the energy they’ve been storing for hundreds of years.
But it’s hard to know the specifics because geologists don’t have the ability to test anything in a lab. All they can do is observe, and geology isn’t quick or predictable, and rarely is it easily accessible.
These slow slippage events happen at such a frequent and regular interval that gives geologists a research opportunity that never happens — the ability to study earthquakes and faults in a present-day context instead of a historical one.
“This phenomenon is very exciting for scientists,” Gao said. “Lots of seismologists think this is the most exciting discovery in a decade.”
Not only is this discovery exciting for seismologists, but it’s also exciting for the entire population of the Cascadia Subduction Zone, because it will help geologists understand what kinds of earthquake hazards we’re facing, so we’re better prepared for “the big one.”
One hypothesis about these slow slippage events is that they help relieve some of the stress the plate is under as it gets compressed under the earth’s surface.
This could mean that the stress is increased in the lock zone, but geologists still aren’t sure.
“Scientists would like to know if this phenomenon will increase or decrease the probability of next megathrust earthquake (in the Cascades),” Gao said.
Another hypothesis, a little scarier than the last one, is that the slip zone — you know, where those rocks snap and release all the energy — might be farther inland than geologists thought. If this hypothesis is true, then the subsequent earthquakes could cause much more damage.
Again, these are all just hypotheses and everything is still under debate.
This concept of “slow earthquakes” only became popular in the early 2000s, so many more years of research are required to know anything for sure.
Until then, we’ll keep our fingers crossed and hope the Juan de Fuca plate can take the pressure.
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