Seismic Slowdowns Could Warn of Impending Earthquakes
An “earthquake machine” in the lab is helping scientists understand what goes on just before a quake
Predicting earthquakes before they happen is the Holy Grail of seismology. If we knew where and when a catastrophic temblor was about to hit, we could evacuate people, turn off gas lines, and shore up infrastructure to protect lives and homes. Unfortunately, like the Holy Grail, earthquake prediction is largely considered a myth—famously called the realm of "fools and charlatans" by seismologist Charles Richter, the man behind the Richter scale.
But now, new research hints that fault zones getting ready to rumble might indeed undergo physical changes that telegraph a quake.
Marco Scuderi, a postdoctoral fellow at Sapienza University of Rome, discovered that he could detect these changes by shooting seismic waves through a laboratory earthquake model. Coupled with real-world analyses of fault zones, this model suggests that monitoring active faults in real time might help scientists develop early warning systems, and maybe even someday forecast devastating quakes before they’ve started. Scuderi and his colleagues published their findings in the journal Nature Geoscience.
Jean-Paul Ampuero, a seismologist at the California Institute of Technology who was not involved in the study, called the study thorough and the results promising. “We need to explore the implications it has on our capability of measuring these precursors before a large earthquake,” he says.
Scuderi never set out to predict earthquakes—and he’s cautious about using the "p-word" when he talks about his work. Instead, he wanted to understand whether regular earthquakes arise from similar processes as their more recently discovered, gentler counterparts known as slow earthquakes.
“We don’t know if fast earthquakes and slow earthquakes are cousins, or if they’re distant relatives, or if they’re just not even related,” explains Scuderi’s co-author and former graduate advisor Chris Marone, a geoscientist at Pennsylvania State University.
So Scuderi turned to a massive, metal earthquake machine about the size of a Volkswagen Beetle to find out. Marone built the first version of this earthquake machine at Penn State in the 1990s, then worked with Scuderi and study co-author Cristiano Collettini at the Sapienza University of Rome to build a second in Italy.
“It looks very big, and very complicated,” Scuderi says. And it is—but he says the rationale behind its inner workings is easy. “With this machine, we just try to reproduce as much as possible what is happening within the Earth.”
Inside the metal behemoth, metal blocks act like tectonic plates sliding past one another, and ground up quartz stands in for the crushed rocks at the interface between the plates. Because earthquakes originate deep in the Earth rather than on a laboratory bench top, the researchers can tweak the horizontal and vertical force exerted on the blocks to replicate pressures at different depths under the Earth’s surface. And to simulate the rigidity or compressibility of the tectonic plates, they can change the stiffness of the spring on the plunger used to push the blocks past each other.
By tweaking the stiffness of the spring and the pressure on the fault, Scuderi could change whether the plates stuck together then slid violently apart like a typical earthquake, or whether they slowly freed themselves over time—more like a slow earthquake. Being able to create the full spectrum of seismic behavior in the laboratory just by changing a few variables told him that slow earthquakes and fast earthquakes might arise from similar physical processes in tectonic faults.
What’s more, before, during, and after the "quake," he shot seismic waves into the fault and measured how they changed as they passed through it. The seismic waves always slowed down right before the fault ruptured—a precursor signal that turns out to have shown up in the real world, too.
Between 2005 and 2006, a research team led by a seismologist from Rice University shot seismic waves through the San Andreas Fault from a bore hole that had been drilled deep underground. When they measured the waves’ velocities as they traveled through the fault, the scientists realized that the waves had slowed before two different quakes. Other studies that simply measured the ambient seismic noise in fault areas detected similar slowdowns around the same time as earthquakes, but weren’t as clear about when exactly these slowdowns happened.
It will be a challenge to actively monitor fault zones for these precursor signals outside of the laboratory. “They’ve found this in the lab at the scale of laboratory experiments,” Ampuero says. “How do you scale that up to a fault that is 100 kilometers long, where the process of preparation for an earthquake happens at 10 kilometers depth?”
Joan Gomberg, a seismologist with the U.S. Geological Survey who was not involved in this research, agrees that trying to detect these precursor signals outside the laboratory won’t be easy—but thinks that Scuderi’s results could mean that it’s worth trying. “If it’s feasible, it’s super exciting,” she says. “It suggests that there could be ways of anticipating a big earthquake, or a destructive earthquake, in the making.”