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While Allen spent most of his time in the UK studying the earth's structure (he described it as "sort of like taking a CAT scan of the Earth"), he slowly became more and more interested in the science of catastrophic shifts in the earth's crust after coming to the United States to get his Ph.D. But it wasn't until 2001, when he moved west to the California Institute of Technology to study with earthquake expert Hiroo Kanamori, that working on real-time forecasting became an actual possibility.
That's not to say that the idea of early alerts for earthquakes was unheard of before Allen and Kanamori came along. As early as the late 19th century, people have postulated that telecommunications could be used to warn people about impending earthquakes.
In 1868, a local physician described his vision for such a system in an op-ed for the San Francisco Daily Evening Bulletin: "A very simple mechanical contrivance can be arranged at various points from 10 to 100 miles from San Francisco," wrote Dr. J.D. Cooper, "by which a wave of the earth high enough to do damage will start an electric current over the wires now radiating from this city and almost instantaneously ring an alarm bell, which should be hung in a high tower near the center of the city."
And until recently, this is essentially the quaint model that was in place. In countries like Mexico and Taiwan, seismometers would detect shaking at its source, and then quickly relay the message to cities many miles away, relying on the fact that the signal — traveling at the speed of light — would outpace the shaking.
But the system that Allen and professor Kanamori would argue for in 2003 boiled down to one major difference: It could detect an earthquake before the shaking hit the Earth's surface, even predicting the magnitude of its shaking.
Their research focused on something called the p-wave. "Our whole planet's crust is moving," explained Jennifer Strauss, spokeswoman for the Berkeley Seismological Laboratory, circling her hands in tandem around an imaginary globe. "And so you have this plate moving this way and this plate moving this way, and because they're all in motion, they all exert pressure at different points." An earthquake occurs when this pressure builds and builds until there is some sort of jutting motion at a point in the plates. The energy released from this sudden collision comes in two waves: the p-wave, a benign but detectable warning, and the s-wave, the source of the potentially deadly shaking.
Though the waves release at the same time, the p-wave travels roughly twice as fast — allowing it to serve as an effective warning. "The p-wave, in effect, carries the information about what's happening, but the s-wave carries the destruction," explained Doug Given, earthquake early warning coordinator for the US Geological Survey.
And while the p-wave can't generally be felt, it's not totally imperceptible. "There's classic videos of earthquakes in Japan where people are at the store, they're buying stuff, and all of a sudden they pause, and they look," Strauss said with a hush, holding her hands up and glancing back and forth. "And then seconds later, the whole thing starts shaking."
But the most important factor is communication speed: Once seismometers stationed along a fault line detect a p-wave, computers then perform some quick calculations, and the system relays the message at the speed of light. Since the shaking wave is traveling at roughly one- to three-miles per second, the warning system is, at its crux, a race against the speed of the oncoming earthquake.
When Allen was on his way to Caltech a dozen years ago, having an early warning system based on p-wave technology didn't exist, nor did the technology required to process and communicate the wave data at such high speeds. Which is why Allen came to work with Kanamori.
"Hiroo Kanamori is considered to be the father of early warning in Japan," Given said. And within the seismology community, Kanamori is viewed as sort of the godfather of the field; among other things, he's credited with coming up with the magnitude scale used almost universally to describe earthquake size. But what really set Kanamori apart from most of the seismology community at the time was that he cared about real-time seismology at all. "Many people in seismology, they just take data from past earthquakes and then look at earthquake processes. So in that sense, it's a little disconnected," said Allen. "But Hiroo was always arguing and advocating for what we could do with real-time seismology. What can you even do in real time? What information can we provide to real people?"
Together, Kanamori and Allen envisioned taking seismology out of the lab and into its real-world applications. After their paper on predicting quakes was published in 2003, interest in the p-wave skyrocketed. "When I started working on it, the vast majority of the seismology community didn't think it was possible. And then as time progressed, it became impossible for them to deny that it was possible," said Allen. "And then the question became, 'Well, how useful is it?'"