Last week, the headlines were particularly frightening. 'Massive Earthquake Along the San Andreas Fault Is Disturbingly Imminent’, ‘Risk of big earthquake on San Andreas fault rises after quake swarm at Salton Sea’, all related to aswarm of earthquakes in the Salton Sea that researchers feared might trigger an epically large earthquake in the area. That earthquake hasn’t materialized (yet) but it raises the question: how well can we actually predict earthquakes?
The swarm in an area known as the Brawley Seismic Zone featured over 96 earthquakes in four days, in an area right near a portion of the infamous San Andreas fault. That particular section of the San Andreas hasn’t moved in about 330 years, which researchers say makes it long overdue for a major quake. Last week, the U.S. Geological Survey stated that the possibility of a 7.0 or larger earthquake in the area was raised to between one and 3,000 and one in 100, much higher than the background risk of about one in 10,000.
The increase in risk triggered an earthquake warning from the California Office of Emergency Services, which led to San Bernardino shutting down its earthquake-vulnerable City Hall , and a lot of anxiety from residents and visitors alike.
Why Was There So Much Concern?Even though a major earthquake didn’t materialize this time, given the public response, it’s worth looking into why the researchers thought that there was a heightened risk.
Ken Hudnut is a geophysicist and the Science Advisor for Risk Reduction for the USGS, and has been studying the area for decades, in particular a 1987 earthquake sequence, known as the Elmore Ranch-Superstition Hillssequence, which was one of the influences for raising the risk of a big earthquake happening in the area last week.
In that case, a quake along a smaller fault happened first, shaking the area. Then, 11 hours later, the larger Superstition Hills fault released, causing a much larger earthquake. The smaller fault was perpendicular to the Superstition Hills fault, a structure known as a cross fault. The sequence of the two faults located so close to each other both in time and place, led researchers like Hudnut to predict that the smaller earthquake had led into the larger one.
“It was an understandable pre-shock, and it made sense. Then, we applied that knowledge to the future and we said ‘If in the future if we have a cross fault earthquake, that might unclamp the San Andreas fault, and you could have a similar pre-shock with a delay'” Hudnut says.
“It’s not like we’re on the brink of being able to actually predict earthquakes.” Hudnut says. Despite decades of research, seismologists are still in the very beginning stages of understanding earthquake processes. They’re still looking at case studies like the 1987 quake, gathering data, observing, and doing their best to understand the complicated physics of major earthquakes, but it isn’t enough to be able to forecast earthquakes like you would a hurricane.
Read more here: www.popsci.com/wait-i-thought-we-couldnt-predict-earthquakes