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Why Can't We Predict Earthquakes?


The ruins of San Francisco's City Hall after the 1906 earthquake and fire. Image Courtesy of the Library Of Congress.

In late October, Italian courts convicted six scientists and a government official—all members of the National Commission for the Forecast and Prevention of Major Risks—of manslaughter for giving "incomplete, imprecise and contradictory" information in the days leading up to an earthquake that struck L'Aquila on April 6, 2009. Tens of thousands of buildings were destroyed, 1000 people were injured, and 308 people died, and the courts believe it was because scientists didn't do enough to warn civilians of the risk of a devastating quake.

Thousands of tiny earthquakes occur every day; some, like the ones that recently hit off the coast of Guatemala, become bigger than others. And no matter what the Italian courts might say, they can’t be predicted. But why?

Earthquakes: How They Work

For centuries, people wondered what caused the Earth to shake. In the 1960s, scientists finally settled on the theory of plate tectonics (more on the origins of the theory can be found here), which posits that the Earth’s surface is built of plates—solid slabs of rock—that move relative to each other on top the hotter, molten material of the outer core. As these plates move around, they slide past and bump into each other; on the boundaries of these plates are faults, which have rough edges and stick together while the rest of the plate keeps moving. When this occurs, the energy that would normally cause the plates to move past one another is stored up, until eventually, the force of the moving plates overcomes the friction on the jagged edges of the fault. The fault unsticks and releases that energy, which radiates outward through the ground in waves, causing an earthquake when the waves reach the surface.

To locate a quake's epicenter—the place on the Earth's surface, directly above the hypocenter, where the quake starts—scientists need to look at the waves produced by the quake. P waves travel faster, and shake the ground first; S waves come next. The closer you are to the epicenter of an earthquake, the closer together those two waves will hit. By measuring the time between waves on three seismographs, scientists can triangulate the location of the quake’s epicenter.

The Challenges of Prediction

Though scientists do create sophisticated models of earthquakes and study the history of quakes along fault lines, no one has enough of an understanding about the conditions—the rock materials, minerals, fluids, temperatures, and pressures—at the depths where quakes start and grow to be able to predict them. “We can create earthquakes under controlled conditions in a laboratory, or observe them close-up in a deep mine, but those are special situations that may not look very much like the complicated faults that exist at depth in the crust where large earthquakes occur,” says Michael Blanpied, associate coordinator of the USGS Earthquake Hazards Program. “Our observations of earthquakes are always at a distance, viewed indirectly through the lens of seismic waves, surface faulting and ground deformation. To predict earthquakes, we would need to have a good understanding of how they occur, what happens just before and during the start of an earthquake, and whether there is something we can observe that tells us than an earthquake is imminent. So far, none of those things are known.”

According to Blanpied, the current understanding is that quakes start—or nucleate—small, on an isolated section of the fault, and then grow quickly. “That nucleation can occur anywhere, and even when we have examples of repeated earthquakes, they may nucleate in different places,” he says. “If there is a process that occurs in the seconds—[or] minutes, hours, months?—before an earthquake, that process may be very subtle and hard to observe through miles of solid rock, especially when we don’t even know where to look.”

Another challenge: Big and small quakes might not start differently. “If all earthquakes start small, and some just happen to grow big, then prediction may be a lost cause, because we’re not at all interested in predicting the thousands of tiny earthquakes that happen every day.”

Prediction vs. Forecasting

Though pinpointing the exact time and size of an earthquake is currently impossible, scientists can estimate the probability of an earthquake occurring in a region or on a fault over a span of decades. “To do that, we need information about how fast the fault is sliding over the long term—typically a few millimeters to centimeters of slip per year—and how big the earthquakes are likely to be,” Blanpied says. “We calculate how much slip is used up in each earthquake, and thus how often earthquakes must occur, on average, to keep up with the long-term slip rate.”

Knowing the date of the last earthquake helps improve forecasting, because scientists can estimate whether they’re early or late based on the repeat time of earthquakes on that particular fault. At the Hayward fault, east of San Francisco Bay, for example, large quakes happen every 140 to 150 years. The last quake on the fault was in 1868, so scientists think that fault could produce another earthquake at any time. “Note, however," Blanpied says, "that ‘any time’ could mean tomorrow or 20 years from now.”

Scientists learned this the hard way. In the 1980s, the USGS predicted that, within 5 years, there would be a magnitude 6 earthquake on the San Andreas fault near the town of Parkfield. “Many types of instruments were deployed in the area to observe the earthquake and also to try to predict it based on various types of precursory signals,” Blanpied says. “As it turns out, the earthquake didn't happen until 2001, which put cold water on the idea of using the timing of past earthquakes to precisely predict future ones. Also, there were no observed precursors, which dimmed the hope that it would be possible to predict earthquakes from observing the ground.”

For now, forecasting is the best we’ve got, and although it’s imprecise, determining the probability of a quake does help developers make good decisions about where to build and what types of forces those buildings should be constructed to withstand. “If our buildings are strong,” Blanpied says, “then it doesn’t matter so much [if we can predict large earthquakes] because we’ll be safe no matter when the ground happens to shake.”

Prediction Research

Quakes pose a threat to 75 million Americans in 39 states, so despite the challenges, scientists at the USGS are working diligently to figure out how to better predict these events. They create quakes in the lab, have drilled boreholes in the San Andreas Fault Zone to get a look at the conditions at depth, and study ground deformation using GPS sensors to understand how stresses build up on faults. At the very least, this research will help create an early warning system similar to Japan’s, which would give people away from the quake's epicenter some time—a few seconds to a minute, maybe—to get to a safe place, slow or halt public transportation, clear traffic off of bridges, and more. But there’s no promise that a solid earthquake prediction method will ever be discovered. “What we need is a prediction method that works better than random educated guessing, and despite decades of work on this problem, so far nobody has demonstrated that such a method exists and works,” Blanpied says. “I am dubious that we will ever be able to predict the time of large earthquakes in a useful way. However, we can predict a lot of things about earthquakes that are useful, other than the time of their occurrence, and we can use that knowledge to make ourselves and our communities resilient.”

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Big Questions
What Makes a Cat's Tail Puff Up When It's Scared?
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Cats wear their emotions on their tails, not their sleeves. They tap their fluffy rear appendages during relaxing naps, thrash them while tense, and hold them stiff and aloft when they’re feeling aggressive, among other behaviors. And in some scary situations (like, say, being surprised by a cucumber), a cat’s tail will actually expand, puffing up to nearly twice its volume as its owner hisses, arches its back, and flattens its ears. What does a super-sized tail signify, and how does it occur naturally without help from hairspray?

Cats with puffed tails are “basically trying to make themselves look as big as possible, and that’s because they detect a threat in the environment," Dr. Mikel Delgado, a certified cat behavior consultant who studied animal behavior and human-pet relationships as a PhD student at the University of California, Berkeley, tells Mental Floss. The “threat” in question can be as major as an approaching dog or as minor as an unexpected noise. Even if a cat isn't technically in any real danger, it's still biologically wired to spring to the offensive at a moment’s notice, as it's "not quite at the top of the food chain,” Delgado says. And a big tail is reflexive feline body language for “I’m big and scary, and you wouldn't want to mess with me,” she adds.

A cat’s tail puffs when muscles in its skin (where the hair base is) contract in response to hormone signals from the stress/fight or flight system, or sympathetic nervous system. Occasionally, the hairs on a cat’s back will also puff up along with the tail. That said, not all cats swell up when a startling situation strikes. “I’ve seen some cats that seem unflappable, and they never get poofed up,” Delgado says. “My cats get puffed up pretty easily.”

In addition to cats, other animals also experience piloerection, as this phenomenon is technically called. For example, “some birds puff up when they're encountering an enemy or a threat,” Delgado says. “I think it is a universal response among animals to try to get themselves out of a [potentially dangerous] situation. Really, the idea is that you don't have to fight because if you fight, you might lose an ear or you might get an injury that could be fatal. For most animals, they’re trying to figure out how to scare another animal off without actually going fisticuffs.” In other words, hiss softly, but carry a big tail.

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Big Questions
What Happened to the Physical Copy of the 'I Have a Dream' Speech?
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AFP, Getty Images

On August 28, 1963, Martin Luther King Jr. stood on the steps of the Lincoln Memorial and gave a speech for the ages, delivering the oratorical masterpiece "I Have a Dream" to nearly 250,000 people.

When he was done, King stepped away from the podium, folded his speech, and found himself standing in front of George Raveling, a former Villanova basketball player who, along with his friend Warren Wilson, had been asked to provide extra security around Dr. King while he was speaking. "We were both tall, gangly guys," Raveling told TIME in 2003. "We didn't know what we were doing but we certainly made for a good appearance."

Moved by the speech, Raveling saw the folded papers in King’s hands and asked if he could have them. King gave the young volunteer the speech without hesitation, and that was that.

“At no time do I remember thinking, ‘Wow, we got this historic document,’” Raveling told Sports Illustrated in 2015. Not realizing he was holding what would become an important piece of history in his hands, Raveling went home and stuck the three sheets of paper into a Harry Truman biography for safekeeping. They sat there for nearly two decades while Raveling developed an impressive career coaching NCAA men’s basketball.

In 1984, he had recently taken over as the head coach at the University of Iowa and was chatting with Bob Denney of the Cedar Rapids Gazette when Denney brought up the March on Washington. That's when Raveling dropped the bomb: “You know, I’ve got a copy of that speech," he said, and dug it out of the Truman book. After writing an article about Raveling's connection, the reporter had the speech professionally framed for the coach.

Though he displayed the framed speech in his house for a few years, Raveling began to realize the value of the piece and moved it to a bank vault in Los Angeles. Though he has received offers for King’s speech—one collector wanted to purchase the speech for $3 million in 2014—Raveling has turned them all down. He has been in talks with various museums and universities and hopes to put the speech on display in the future, but for now, he cherishes having it in his possession.

“That to me is something I’ll always be able to look back and say I was there,” Raveling said in the original Cedar Rapids Gazette article. “And not only out there in that arena of people, but to be within touching distance of him. That’s like when you’re 80 or 90 years old you can look back and say ‘I was in touching distance of Abraham Lincoln when he made the Gettysburg Address.’"

“I have no idea why I even asked him for the speech,” Raveling, now CEO of Coaching for Success, has said. “But I’m sure glad that I did.”

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