by Brooks Hays
Washington (UPI) Sep 29, 2017
In the last month, two earthquakes have rocked Mexico. On Sept. 7, a magnitude 8.2 earthquake struck the coast of Chiapas, Mexico's southernmost state. The quake killed 98 people. Two weeks later, an unrelated earthquake rattled Mexico City. The magnitude 7.2 quake killed at least 230 people in Mexico's sprawling capital.
In the wake of the two disasters, some have wondered whether the pair of quakes could have been predicted.
Some suggest seismologists in Mexico were focused on the dangers posed by the Guerrero Gap, a section of fault line along the Pacific coast near the resort town of Acapulco.
As the Mexican newspaper El Universal warned in March, the gap is "named for the fact that more than 100 years have passed without a significant seismic event."
But last week's quake wasn't triggered by a slip in the Guerrero Gap. The rumblers were triggered by a rupture deep beneath the mountains of central Mexico.
Scientists became preoccupied with the Guerrero Gap after a nearby fault slip triggered the 1985 earthquake that toppled skyscrapers and killed some 10,000 people in Mexico City. Because the Guerrero Gap hadn't broken in decades, seismologists assumed it was only a matter of time.
Some scientists now believe long periods of dormancy alone aren't reason to suspect impending disaster. In fact, some research suggest seismologists pay closer attention to fault lines that rupture frequently.
In Japan, scientists worried that a slip along the Tokai Gap could destroy Tokyo, but in 2011, a separate less-studied fault triggered the Tohoku earthquake that inspired a massive tsunami and killed 15,894 people.
Men-Andrin Meier, a postdoctoral researcher in Caltech's Seismology Lab, says the realization that earthquake risk doesn't just come from the big faults predates the latest Mexican rumbles.
"California realized this in the devastating 1994 magnitude 6.7 Northridge earthquake," Meier told UPI. "Before that people were focused mainly on the very big earthquakes that can occur on the San Andreas Fault, but then in 1994 a much smaller -- but still pretty big -- earthquake happened right underneath LA and caused what was then the worst natural disaster in the history of the U.S."
"Today, I think there is a broad realization that in most seismically active areas destructive earthquakes can occur almost anywhere," Meier added. "In California about half the earthquakes that caused damage occurred on faults that were previously unknown."
And therein lies the rub. In being caught off-guard, seismologists in Mexico aren't alone. Most earthquakes are a surprise. But what if seismologists in Mexico had been paying closer attention to the deep-lying faults beneath central Mexico? Would they have been able to predict the latest quake? Most scientists would say no.
"My view is that we're not at all close to being able to predict earthquakes," Jeanne Hardebeck, a research geophysicist at the USGS's Earthquake Science Center in Menlo Park, Cal., told UPI. "There has been a lot of work over the years looking for predictive precursory signals, which has failed to find a signal that is a reliable predictor of a coming earthquake."
Peggy Hellweg, director of operations at the University of California's Berkeley Seismological Laboratory, agrees that true earthquake prediction is currently beyond scope of science.
"We do not yet have the equipment -- or even know what is needed -- to know all the parameters in the earth that affect when, where and how big an earthquake will be," Hellweg told UPI.
More than a lack of equipment, scientists admittedly have a lack of knowledge. Seismologists are still working to understand the physics of earthquakes.
"We can't observe earthquake processes directly because they occur deep within the earth," Hardebeck said. "If we knew the relevant physics and could better observe the system, then physics-based earthquake forecasting -- similar to weather modeling -- might be possible."
Some scientists are using machine learning algorithms to analyze seismic data, and to find important fault slip signatures among the statistical noise. But while these endeavors could help scientists better understand how earthquakes behave, so far, they haven't proven capable of predicting earthquakes.
"So far, all proposed precursory signals have not been confirmed to work in even 50 percent of the cases," Hellweg said. "Or, they may occur all the time and only in a few cases does a big quake follow."
Of course, an inability to predict a seemingly unpredictable geologic phenomenon doesn't discredit the efforts to study and understand seismic activity. But when facing a threat that can raze cities and kill thousands, it's only natural to seek the wisdom of the experts. So what can seismologists do to help citizens, public safety officials, first responders, engineers and others prepare for and prevent property damage and human injury?
While earthquake scientists can't yet predict earthquakes, they have improved early warning systems.
"We have made progress on Earthquake Early Warning, alerting people quickly when an earthquake happens, which may give them seconds or even minutes to get ready before the shaking reaches their location," Hardebeck said, referring to a warning system used by Japan.
"This is how the earthquake alarms in Mexico City work," she said. "A similar system is being developed for the U.S. West Coast."
By studying how seismic waves travel through different types of rock and what frequencies at-risk acreage is most likely to vibrate at, seismologists can help city officials and engineers develop improved building codes.
Still, some countries situated along the Ring of Fire, a region of heightened seismic activity, can't afford to update infrastructure. And new types of temblors can take cities by surprise.
As is often the case when scientific questions are raised, the answer is more science. While scientists may still be a ways away from predicting earthquakes, with more data, researchers might begin to develop more accurate forecast models.
Meteorologists are often the butt of jokes, but weather forecasting has improved dramatically over the last several decades. Most of the improvements can be explained by the increase in accurate weather-related data scientists now have -- data on cloud cover, temperature, wind, air pressure and more.
The mechanics of fault lines occur in three dimensions across vast distances and over huge swaths of time. The efforts to record and measure these mechanics are growing in scope, but they are capturing only a small percentage of the data that's out there.
"We are using seismic waves from a variety of sources to get some very, very 'big picture' estimates of what is happening in the earth," Hellweg said. "Because of the sparse nature of those measurements, we need to average over long times. Ideally, we would have sensors 'everywhere,' measuring 'everything' -- 'all the time.' We don't yet know what 'everything' is or what time scales are important."
Until then, the best scientists can do is use statistical and historical analysis to offer a rough estimate for where, when and how powerful the next quake will be.
Hellweg has a canned response for those who ask her when the next big one will come from the Hayward Fault Zone, which runs through the east side of the San Francisco Bay.
"It can happen with high likelihood anytime in the next 30 years," she tells them. "Do I expect it to happen tomorrow? No. Would I be surprised if it happened tomorrow? No."
Mexico City (AFP) Sept 20, 2017
Rescuers dug frantically Wednesday for survivors of a 7.1- magnitude earthquake that killed more than 200 people in Mexico, as the nation watched anxiously for signs of life at a collapsed school in the capital. The death toll stood at 225, the head of the national disaster response agency, Luis Felipe Puente, wrote on Twitter. President Enrique Pena Nieto warned the figure would likely rise ... read more
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