The last and best hope for earthquake prediction

The three words were written in capital letters on the evening news, next to the anchor's hairstyle: “BIG.” There was a map of Southern California hovering just below, outlined by concentric red circles. I'm pretty sure it was 1988. The area was inundated with warnings about the next big earthquake. They were like something out of the book of Isaiah. They gave a terrible crackle to sunny days. My generation reached school age too late to participate in atomic attack drills, and too early for those simulating school shootings, but we learned to avoid and cover up just the same.

In 1989, we saw a vision of our future. An earthquake struck the Bay Area, and for more than a week, the entire state was immersed in images of the seismic disaster. A highway overpass was cut in half. He overthrew some of the pastel Victorians in San Francisco. A fire broke out in the marina. The World Series – an event of great importance and inevitability in the child's mind – was stopped. “What's big is supposed to be worse,” we whispered to ourselves and to each other. In the psychogeography of Southern California, he was sleeping like a beast deep beneath the surface of the earth. Any minute, maybe soon, he'll wake up.

It still hasn't happened. The San Andreas Fault formed about 30 million years ago, when the Pacific Plate — the largest on the planet — began grinding against the North American Plate. Sometimes, the plates break down. The tension builds until they release with a swing that sends energy in all directions. The part of San Andreas that runs along Los Angeles has not suffered a terrifying earthquake in more than three centuries. Paleoseismologists expect large quakes there to occur every 150 to 200 years, and Greg Perosa, a professor at Stanford University and co-director of the Southern California Earthquake Center, told me: “We're late.” He said that teams of scientists are trying to improve these frighteningly vague forecasts, so that the arrival of an earthquake can be predicted days, weeks, or even months in advance – but there is no guarantee that they will succeed.

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At the turn of the 20th century, California was home to few seismometers, especially inside domed observatories atop mountaintops, where they took advantage of astronomers' ultra-precise clocks. But after the United States and the Soviet Union agreed in 1963 to stop above-ground nuclear weapons testing, the Pentagon suddenly became very eager to fund new seismic sensors. Since then, scientists have spread more than 1,000 of them across the surface of California, in both major cities and wilderness areas. They pick up a lot of noise. East of Los Angeles, in the San Bernardino Mountains, they detected the rumble of falling rocks. At downtown construction sites, they record the rumble of pickup trucks and jackhammers.

Algorithms sift through this noise in real-time data analysis centers, looking for P waves, the fast-moving ripples of seismic energy that first push outward from fault slip. These waves are a nice advertisement for the upcoming, more destructive S waves. When enough of them are detected, automated processes are triggered. Millions of push notifications appear on mobile phone lock screens. The stop lights are red, and the gas valves are closed. Metro cars stop instead of entering the tunnels. “The speed of communications is faster than seismic waves,” Peroza told me. “You only have seconds, but that's enough time to get out before the vibration.”

Scientists hope new technologies will give us a longer warning window. If deep learning algorithms are trained on enough seismic data, they may be able to reliably detect sequences of activity that precede earthquakes. The forecasting record of these techniques so far has been disappointing, says Zachary Ross, a geophysicist at the California Institute of Technology. He told me that a similar approach has had great success in meteorology. AI-based methods can detect patterns in atmospheric data that help predict storms, but they cannot yet guess when two plates might slide along a fault.

I was surprised to hear that it is easier to predict the ethereal movements of wind and rain than the great shifts in the harsh, subterranean world of rock. Meteorologists have better data, Ross told me. They constantly measure the state of the atmosphere with high precision, while seismologists are more limited in the type of data they can collect, at least for now. Christopher Johnson, a research scientist at Los Alamos National Laboratory, uses a hydraulic ram to push the 10-centimetre-diameter granite blocks together, until they slide over each other like tectonic plates. It measures seismic energy radiating outward, and is able to generate a lot of data, because these experiments can be repeated with new blocks in quick succession. But there are serious challenges in extrapolating their results to actual earthquakes that occur over much larger scales of space and time. New data is also pouring in from new types of sensors, including inexpensive sensors that seismologists deploy above ground in temporary arrays along particularly active parts of faults. They are also turning existing fiber-optic networks into seismometers, by measuring changes in the way laser light bounces off of them when the ground shakes.

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These new data sources are interesting, Ross says, but he doesn't expect them to produce any breakthroughs in earthquake prediction. He said emerging technologies suffer from the same problem as established technologies: all the sensors are placed too far away from the action. California's seismic sensors are at ground level, but the fault slips that cause many of the state's earthquakes begin six to eight miles below the surface. The resulting seismic waves radiate outward in the form of a sphere. Some of it moves down through the thick molten mantle and core until it reaches the other side of the planet. (“Anything above 5 on the Richter scale can be detected almost everywhere on Earth where there is a seismometer,” Ross told me.) Other waves rush toward the surface directly above the fault. The problem is that no matter where these waves appear on the surface, they must first pass through the last outer mile of the crust, which is punctuated by cracks, loose rocks and oozing fluids. “Approximately 90% of the energy of these waves is absorbed at the upper slope or so,” Ross said. Seismologists can tell that an earthquake has occurred, but they cannot observe its more subtle characteristics.

“All we do now is remote sensing,” Peroza told me. If we want to get clearer glimpses of earthquakes—and the potential predictive seismic activity that precedes them—we need to place sensors beneath this upper layer of the Earth's crust. Japan's seismic network is the envy of the world, in part because its scientists have installed their sensors deeper into the planet. After the Kobe earthquake killed more than 6,000 people in 1995, the country's political leaders encouraged data sharing among seismologists and funded the drilling of wells throughout the archipelago. Each one extends to a depth of a few hundred feet.

It's a good start. At this depth, the sensors experience much less noise. But seismic waves are still distorted and weak when they reach Japanese well sensors. Ideally, they would be placed miles and miles away, where earthquakes originate, but that part of the interior is as inaccessible as outer space, Peroza told me. Even placing equipment a mile away would be very expensive. Any well of this depth would be in constant danger of closing in on itself, due to the intense pressure. They may also be filled with corrosive liquids and gases. However, this type of drilling has only been performed in a few one-off projects. If successful, sensors could be lowered beneath the top layer of the crust and would be able to record aspects of the earthquake that cannot be observed on the surface.

“The most immediate hope is that there is some signal in smaller seismic activity that would herald larger earthquakes,” Peroza said. But scientists may also pick up new types of seismic waves, or new patterns of activity. Any breakthrough in forecasting would likely arise from a signal we haven't seen before and don't expect, Ross told me. But even if we spend decades listening closely to the great beast lying asleep beneath California, we may never hear any snoring pattern that indicates it is about to wake up. We may be forever vulnerable to adults.

I wished for better news. I no longer live in Southern California, but I am still connected to it spiritually and through family. Fear of the big event is a common psychological experience for those who grew up in the area. I still remember worrying about it with friends on the playground and late at night while sleeping. Like the Night Stalker, it seemed like a very localized generational concern, a subject of anxiety that was uniquely ours. But we got through it. All these years later, the forecasts haven’t changed: Experts still give odds that a major earthquake will shake the towers of downtown Los Angeles and the surrounding area, with great force, sometime in the next 30 years. When my young niece and nephew go to school, they may also learn to fear the big guy. Part of growing up in California, or anywhere else, is learning that science has its limits. Nature can never be fully known or tamed.

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