Laura Bliss is CityLab’s West Coast bureau chief. She also writes MapLab, a biweekly newsletter about maps (subscribe here). Her work has appeared in The New York Times, The Atlantic, Los Angeles magazine, and beyond.
A controversial paper determines there’s a 99.9 percent chance that a large earthquake will strike the region in the next three years.
A paper authored by a JPL scientist makes a controversial, pronouncement: In the Los Angeles region, the probability of an earthquake of a 5.0 or greater magnitude occurring in the next three years is 99.9 percent.
Published last month by the American Geophysical Union’s Earth and Space Science journal, the paper examines the potential for a large earthquake along the fault lines of the 2010 La Habra earthquake, a 5.1 magnitude quake in the L.A. area.
Andrea Donnellan, the study’s lead author and a principal research scientist at NASA's Jet Propulsion Laboratory, says that the thrust of the paper was not to forecast L.A.’s next ‘big one.’ It was to show how new NASA-developed GPS and radar technologies developed can be used to detect how much energy lies latent below the earth’s surface following a quake. Based on what the technology revealed about the La Habra region, Donnellan says that her team found a potential for an earthquake between 6.1 and 6.3 magnitude. But she didn’t attach that probability to a time window.
“When you pull on a rubber band, you don’t know when it’s going to break, but you know it’s going to,” Donnellan says. “And if you pull harder you’re going to have a bigger snap.”
But as a way to confirm and compare the results of the new technique, the study also used historical seismic data to determine the probability of a large quake occurring within the near future. Given that there were 32 magnitude five-or-above earthquakes in the region over the last 81 years, the authors determined the chances of another one occurring in the next three years is 99.9 percent.
Local seismologists have taken issue with that calculation. The U.S. Geological Survey has criticized the paper for its relative lack of detail on how it derived that probability. Lucy Jones, a USGS seismologist and L.A.’s official ‘earthquake czar’, told KPCC’s Sanden Totten that the paper’s methodology doesn’t fully account for that 99.9 percent probability, and that that number doesn’t match her agency’s. KPCC reports:
The USGS conducts its own look at quake risk in California—the most recent version is called Uniform California Earthquake Rupture Forecast, Version 3.
Jones said that, according to those models, there is only an 85 percent chance of a magnitude 5 or 6 quake in the same region over a three-year period.
"It's nowhere near a 99.9 percent number," Jones said.
Still, an 85 percent chance is still very high—and many previous reports have noted that the L.A. region is overdue for a large earthquake. Donnellan’s paper may be particularly alarming by asserting near-certain probabilities, but the message is nothing new: Southern California should be on alert for a big one.