There Have Been a Lot of Earthquakes Lately. Don’t Panic.
It could all just be coincidence.
We’re only a month into 2018, but natural disasters like earthquakes, tsunamis, and volcanoes have made a lot of headlines thus far. The past week alone has seen several seismic events: The Philippines’ Mount Mayon erupted last Monday, forcing the evacuation of more than 75,000 people. The day after, a 7.9-magnitude earthquake struck off the coast of Alaska, lighting up Pacific tsunami warning systems as far away as San Diego. That same day, a volcano erupted near a Japanese ski hill, killing one person and injuring many others. Two days later, a quake rattled Los Angeles, and another two struck in close proximity off the coast of Northern California.
These events, taken together, signal that Earth’s Ring of Fire is waking from its slumber, and that more, bigger catastrophes are on the way—that is, if the proliferation of alarmist headlines that have followed is to be believed.
“You get every Tom, Dick, and Harry writing down all sorts of crazy things about: ‘The big earthquake is coming,’” Stephen Malone, a seismologist with the Pacific Northwest Seismic Network and professor emeritus with the University of Washington told The Daily Beast. “Well, yes, it is coming, but not necessarily any sooner because of the recent earthquakes.”
Every great lie is built on a foundation of truth. It’s true that the San Andreas Fault will one day unleash a great quake on southern California. We also know that the Cascadia Subduction Zone will one day unzip, sending a megathrust earthquake and tsunami at breakneck speeds toward the Pacific Northwest. It’s true, too, that earthquakes in one place can trigger more far away, over thousands of miles. It may even be true that the worldwide coincidence of major quakes is more than coincidence, that there are global patterns that bring disaster into sync.
But the bigger truth is that scientists still don’t know enough about the fundamental physics of earthquakes to predict with precision and certainty when a seismic event will happen. Earthquakes aren’t entirely random, but for the purpose of day-to-day threat assessment, they may as well be.
And, it should be said, that the seismic events of the last few weeks are hardly anomalous. “If you go on the worldwide catalog of earthquakes at the USGS on the web, you will see that there’s earthquakes going on all over the world, all the time,” Malone said. “Any sort of random sequence of events will have times when things are clustered and times when they’re not.”
Earthquakes can trigger more earthquakes, but the known ways this happens are limited. Quakes occur in the places where tectonic plates move and grind against one another; when that pressure builds to a breaking point, the fault shifts and the ground shakes. But some of that stress can be moved to other parts of the fault, where it may push it past the breaking point again, setting off another earthquake. Normally, the subsequent quakes are smaller, and are called aftershocks. In the rarer cases where later tremors are stronger, the first becomes a foreshock.
Over longer distances, there’s evidence a big quake can set off smaller ones, although the mechanism isn’t well understood. It isn’t by directly impacting the stresses at the fault, so it must be an effect of the shockwaves coming through. Paul Bodin, a seismologist at the Pacific Northwest Seismic Network and the University of Washington, said he expects it works a bit like tapping a window that’s stuck with a hammer to jostle it open.
But even a very large quake on the other side of the planet is unlikely to set off the Big One close to home. “There’s little to no evidence for triggering of large earthquakes across vast tracts of land,” Bodin said.
And as for earthquakes setting off a global spewing of lava, it just doesn’t seem to happen, not even locally. Although both earthquakes and volcanoes are most active at tectonic plate boundaries, their interactions are limited. “There’s very, very scant evidence that big earthquakes can influence the eruption of a volcano,” Bodin said. “Which I actually find kind of surprising because it seems to me that after a big subduction zone earthquake, like 2011 in Japan, I can imagine all the volcanoes going off at once. But that doesn’t happen and it’s very difficult to find any evidence that it ever happens.”
Seismologists are working on the finer details of earthquake probabilities and risk, but the resolution is still coarse. “If you look at the whole earthquake catalog, it’s just a big mess of events,” Rebecca Bendick, a geophysicist at the University of Montana, said. “It’s incredibly hard to forecast earthquake risk beyond saying, OK, we know earthquakes happen on faults and certain places are more active than others. Beyond that, it’s been difficult to say anything more.”
However, Bendick recently found a pattern in that noise. She and colleague Roger Bilham, a geophysicist at the University of Colorado at Boulder, recently presented evidence that major earthquakes synchronize themselves according to tiny, periodic shifts in Earth’s rotation that occur as the planet’s molten inner bits effectively slosh around the solid core. Five to seven years after a minute rotational slowdown, we tend to see more magnitude-7 or higher quakes. These activity peaks occur once about every three decades. While an average year might see 14 or 15 big quakes, in a peak year that could go up to 22 or 23, she says.
There’s still a lot of variability and noise in the data, but the pattern is clear enough that, statistically, there’s less than a 1-in-100 chance of it cropping up in a purely random system, Bendick said. The research is still in the process of peer review, but ultimately time will be its most important critic: If Bendick is right, there should be a spike in major quake activity beginning this year, and peaking around 2020. “It’s the gold standard of science, right? You say something will happen as a consequence of your ideas, and then you wait and see if it does or not. That’s a pretty strong test.”
There have been three magnitude-7 quakes in 2018, just a few weeks in. That’s a lot, but it’s impossible to say based on that what the rest of this year will hold. And, even if the coming months continue to be shaky, the implication for any particular seismic event is still limited.
If there are 50 percent more major quakes this year than an off-peak year, then it may be fair to conclude that the likelihood of any particular major quake occurring this year also rises by 50 percent, at least on average.
That sounds huge, but for a event that has a very low probability to begin with, it’s peanuts. For example, if the likelihood of the Big One going off this year goes from 1-in-1,000 to 1.5-in-1,000, it’s unlikely that many West Coasters will put their houses up for sale and set their sights further east.
The best course of action, for those who live near faults with significant potential for devastation, is to understand and be prepared for a worst case scenario could happen at any time. The thing is, it’s unlikely to occur at any particular time.