Angelenos live under constant threat of a major earthquake, but a controversial new study from NASA's Jet Propulsion Laboratory puts a number on that threat. The scientific paper claims there is a 99.9 percent chance of an earthquake between magnitude 5 and 6.3 in less than three years.
The study was published earlier this month by the American Geophysical Union's Earth and Space Science journal. The bold claim has taken many in the seismic community by surprise.
Lead author, Andrea Donnellan of JPL, said this study used GPS and airborne radar data to look at land deformation caused by last year's 5.1 La Habra earthquake. Her team determined that, based on the surface changes, there is still a fair amount of pent-up seismic energy in the region that needs to be released.
“It’s almost like using the surface of the Earth as an instrument to understand what is going on deeper," she explained.
That energy could spawn shaking associated with a magnitude 5 or 6 temblor, she added, but that energy could crop up on any number of faults within a 100-kilometer range of last year's quake.
This sort of prediction is quite common. What isn't common is claiming a 99.9 percent chance of such a quake in a window of time as small as three years.
Donnellan said her team arrived at the conclusion by looking at the number of magnitude 5 earthquakes in the region over the last 81 years. There were 32 such events.
“So if you just look at that on average, it's about an earthquake every three years," Donnellan said.
Lucy Jones with the U.S. Geological Survey said that methodology doesn't fully explain the prediction, and the study doesn't adequately address this either.
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.
USGS released a statement on its Facebook page saying that the lack of details on how this number was reached "makes a critical assessment of this approach very difficult."
While the AGU journal the JPL paper appeared in conducts peer review of studies, Jones said it's custom that quake prediction studies are also sent to the National Earthquake Prediction Evaluation Council or its California counterpart.
However, she said this paper was not submitted to those organization for review. She added that there is no scientific consensus on this issue.
"This is the opinion of a small group of scientists — it has not been reviewed for action as a prediction, and I wouldn't be changing any behavior on the basis of this study," Jones said.
Several earthquake researchers approached by KPCC said they were surprised by this study and its conclusions, among them Michael Blanpied with the USGS Earthquake Hazards Program.
However, he noted that it should come as no surprise to people in Southern California that earthquakes are a real threat to the region.
“But I would say in general we want to give them the most credible and authentic information that we can,” he added.
JPL's Donnellan defended the research, saying that it's now up to the larger scientific community to evaluate the claims and see if different ones are called for.
“In science, individual methods are always controversial to somebody, but that’s how we make forward progress,” she said.
The study, titled "Potential for a large earthquake near Los Angeles inferred from the 2014 La Habra earthquake," was first published by AGU online on Oct. 1.
This story has been updated.