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Earthquake 'thermometer' shows LA region is boiling to Northridge level

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Earthquake ‘thermometer’ shows LA region is boiling to Northridge level

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In this Jan. 17, 1994, file photo, the covered body of Los Angeles Police Officer Clarence Wayne Dean lies near his motorcycle which plunged off the State Highway 14 overpass that collapsed onto Interstate 5, after a magnitude-6.7 Northridge earthquake in Los Angeles. (AP Photo/Doug Pizac, File)

By Jason Henry, Southern California News Group |

PUBLISHED: September 26, 2017 at 10:34 am | UPDATED: September 26, 2017 at 10:37 am

The Los Angeles region’s “earthquake potential score,” a gauge for assessing the likelihood of a destructive temblor, has surpassed the level assigned to the 6.7 magnitude Northridge Earthquake of 1994, according to a University of California Davis professor.
The score is created through “nowcasting,” a method of using small earthquakes to mark the current progress between larger and more dangerous ones, according to John Rundle, a professor of geology and physics at UC Davis. Rundle developed the idea in collaboration with researchers from UC Irvine and the Jet Propulsion Laboratory.
“The data says that within 100 kilometers of Los Angeles, as judged by the number of small earthquakes, we are in the same state of hazard as we were just prior to Northridge,” Rundle said.
The Northridge Earthquake killed dozens, injured more than 8,000 people and disrupted life in Los Angeles and the surrounding counties for months. Though the score gives a sense of risk, Rundle stressed nowcasting, unlike forecasting, doesn’t attempt to predict when the next earthquake might hit or how damaging the quake could be.
Since 1933, three earthquakes with a magnitude larger than 6 have occurred in Los Angeles, with 23 to 38 years separating each. Northridge struck a few months shy of 24 years ago today.
Last year, Rundle and his co-authors published their research on nowcasting in “Earth and Space Science.” In an update this week, Rundle calculated the earthquake potential score, or EPS, just before Northridge was at 77.8 percent. There were 34 earthquakes, with greater than a 4.5 magnitude, between the previous 6.6 magnitude San Fernando Earthquake in 1971 and the subsequent 1994 quake.

This graph, created by John Rundle of UC Davis, shows the “earthquake potential score” or EPS, at the time the Northridge Earthquake occurred in 1994. (Courtesy of John Rundle) 

By comparison, Los Angeles’ EPS is currently at 80.3 percent, with 31 earthquakes greater than a 4.5 magnitude between 1994 and Friday.

This graph, created by John Rundle of UC Davis, shows the current “earthquake potential score” in the Los Angeles Region. The score is already above the threshold before Northridge earthquake occurred. (Courtesy of John Rundle, UC Davis) 

“This does not necessarily mean that a (greater than magnitude 6) earthquake will occur in the near future in that region, it could be years away,” Rundle said in an email Friday. “But given the fact that there have been 3 such events in the last century (the 1933 Long Beach, the 1971 San Fernando, and the 1994 Northridge), you can depend on the fact that such an earthquake will occur at some point.”

With nowcasting, the risk only increases with more time. Each small earthquake raises the score and it only resets to zero once the larger quake occurs. Nowcasting isn’t a scientific model, instead Rundle described it as a simple and broad interpretation of regional data that does not factor in the complexities of the area’s earthquake faults.
Lisa Grant Ludwig, a professor of public health at UC Irvine and a co-author on the study, prefers to think of nowcasting as a snapshot of “where we are now.” She compared the hazard rating to looking out the window, seeing the light dimming and knowing the sun will set, even if you don’t know what time exactly.
“We’re not bright and early in the morning. We’re getting late in the day,” she said. “The earthquake potential is uncomfortably high, anyway you look at it.”
Ludwig’s background is in geology, but she switched her focus to public health because she wanted to motivate people to prepare for the inevitable.
“We’re never going to be able to stop earthquakes, they’re going to happen no matter what,” she said. “We have to act before, not after.”
The idea behind the earthquake potential score is to make it easier to understand the threat. The calculations could be used to display hazard levels in real time for major cities around the world. The researchers have toyed with a website that would display each city’s score, but it isn’t yet publicly available.
If the earthquake potential score is a thermometer, we’re getting “uncomfortably warm,” Ludwig said. Now, particularly in light of recent natural disasters, is the time to prepare, by creating an emergency supply kit and a disaster plan, she said.
“People don’t like to deal with it, but the impact, when it happens, will depend in a large part on what we did, or did not do, before the earthquake,” she said.
For more information about emergency kits and how to prepare, visit www.bepreparedcalifornia.gov, or the Great Shakeout’s website, shakeout.org.