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Why Can't We Predict Earthquakes?

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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
Why Do Cats Love Scratching Furniture?
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Allergy suffering aside, cat ownership has proven health benefits. A feline friend can aid in the grieving process, reduce anxiety, and offer companionship.

The con in the cat column? They have no reservations about turning your furniture into shredded pleather. No matter how expensive your living room set, these furry troublemakers will treat it with the respect accorded to a college futon. Do cats do this out of some kind of spite? Are they conspiring with Raymour & Flanigan to get you to keep updating home decor?

Neither. According to cat behaviorists, cats gravitate toward scratching furniture mostly because that love seat is in a really conspicuous area [PDF]. As a result, cats want to send a message to any other animal that may happen by: namely, that this plush seating belongs to the cat who marked it. Scratching provides both visual evidence (claw marks) as well as a scent marker. Cat paws have scent glands that can leave smells that are detectable to other cats and animals.

But it’s not just territorial: Cats also scratch to remove sloughed-off nail tips, allowing fresh nail growth to occur. And they can work out their knotted back muscles—cramped from sleeping 16 hours a day, no doubt—by kneading the soft foam of a sectional.

If you want to dissuade your cat from such behavior, purchasing a scratching post is a good start. Make sure it’s non-carpeted—their nails can get caught on the fibers—and tall enough to allow for a good stretch. Most importantly, put it near furniture so cats can mark their hangout in high-traffic areas. A good post might be a little more expensive, but will likely result in fewer trips to Ethan Allen.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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Big Questions
Who Was Chuck Taylor?
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From Betty Crocker to Tommy Bahama, plenty of popular labels are "named" after fake people. But one product with a bona fide backstory to its moniker is Converse's Chuck Taylor All-Star sneakers. The durable gym shoes are beloved by everyone from jocks to hipsters. But who's the man behind the cursive signature on the trademark circular ankle patch?

As journalist Abraham Aamidor recounted in his 2006 book Chuck Taylor, All Star: The True Story of the Man behind the Most Famous Athletic Shoe in History, Chuck Taylor was a former pro basketball player-turned-Converse salesman whose personal brand and tireless salesmanship were instrumental to the shoes' success.

Charles Hollis Taylor was born on July 24, 1901, and raised in southern Indiana. Basketball—the brand-new sport invented by James Naismith in 1891—was beginning to take the Hoosier State by storm. Taylor joined his high school team, the Columbus High School Bull Dogs, and was named captain.

After graduation, instead of heading off to college, Taylor launched his semi-pro career playing basketball with the Columbus Commercials. He’d go on to play for a handful of other teams across the Midwest, including the the Akron Firestone Non-Skids in Ohio, before finally moving to Chicago in 1922 to work as a sales representative for the Converse Rubber Shoe Co. (The company's name was eventually shortened to Converse, Inc.)

Founded in Malden, Massachusetts, in 1908 as a rubber shoe manufacturer, Converse first began producing canvas shoes in 1915, since there wasn't a year-round market for galoshes. They introduced their All-Star canvas sports shoes two years later, in 1917. It’s unclear whether Chuck was initially recruited to also play ball for Converse (by 1926, the brand was sponsoring a traveling team) or if he was simply employed to work in sales. However, we do know that he quickly proved himself to be indispensable to the company.

Taylor listened carefully to customer feedback, and passed on suggestions for shoe improvements—including more padding under the ball of the foot, a different rubber compound in the sole to avoid scuffs, and a patch to protect the ankle—to his regional office. He also relied on his basketball skills to impress prospective clients, hosting free Chuck Taylor basketball clinics around the country to teach high school and college players his signature moves on the court.

In addition to his myriad other job duties, Taylor played for and managed the All-Stars, a traveling team sponsored by Converse to promote their new All Star shoes, and launched and helped publish the Converse Basketball Yearbook, which covered the game of basketball on an annual basis.

After leaving the All-Stars, Taylor continued to publicize his shoe—and own personal brand—by hobnobbing with customers at small-town sporting goods stores and making “special appearances” at local basketball games. There, he’d be included in the starting lineup of a local team during a pivotal game.

Taylor’s star grew so bright that in 1932, Converse added his signature to the ankle patch of the All Star shoes. From that point on, they were known as Chuck Taylor All-Stars. Still, Taylor—who reportedly took shameless advantage of his expense account and earned a good salary—is believed to have never received royalties for the use of his name.

In 1969, Taylor was inducted into the Basketball Hall of Fame. The same year, he died from a heart attack on June 23, at the age of 67. Around this time, athletic shoes manufactured by companies like Adidas and Nike began replacing Converse on the court, and soon both Taylor and his namesake kicks were beloved by a different sort of customer.

Still, even though Taylor's star has faded over the decades, fans of his shoe continue to carry on his legacy: Today, Converse sells more than 270,000 pairs of Chuck Taylors a day, 365 days a year, to retro-loving customers who can't get enough of the athlete's looping cursive signature.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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