Earthquake Prediction: Slight Changes in Magnetic Field Preceded California Earthquakes

The researchers found detectable changes in the local magnetic field that occur 2-3 days before an earthquake.

Magnetometers have detected weak signals that can improve our understanding of what happens before earthquakes and promise early detection.

Scientists studying intermediate to large earthquakes in California have found detectable changes in the local magnetic field that occur 2-3 days before an earthquake. A recent study found that the signal from the changing magnetic field is small but statistically significant, and seismologists hope their technique can be refined to eventually help predict earthquakes. The research was recently published in the Journal of Geophysical Research: Solid Earth.

“It’s a modest signal,” said study co-author Dan Schneider. He is director of QuakeFinder, an earthquake research arm of Stellar Solutions, a systems engineering services company. “We don’t claim this signal exists before every earthquake, but it is very intriguing.”

The magnitude 6 earthquake in South Napa, California in August 2014 caused the ground to rupture in places, including this vineyard. Credit: US Geological Survey

Although always controversial, the idea that the magnetic field can move before earthquakes has been around for some time. The US Geological Survey (USGS) states that “despite decades of work, there is no compelling evidence for electromagnetic precursors to earthquakes”.

The researchers searched for data from 125 magnetometer sensor stations, like this one, located along major faults in California, looking for signals of magnetic field changes that occurred before the earthquakes. 1 credit

Working with the Google Accelerated Science team, the scientists tapped into magnetic field data from an array of magnetometers at 125 sensing stations along major fault lines in California. They collected data from 2005 to 2019, during which time 19 earthquakes of magnitude 4.5 or greater occurred on the faults.

Their multistation analysis took into account other types of processes that could affect magnetometers but have nothing to do with earthquakes, such as rush-hour traffic. According to Schneider, differentiating this type of noise from potential signals related to earthquakes is the biggest obstacle to interpreting this data. After training their algorithms on half of the dataset, the researchers identified a signal indicating changes in the magnetic field between 72 and 24 hours before the earthquakes.

Schneider said that in the future he would like to further refine the models to remove more ambient noise from the magnetometers. In this study, for example, taking into account the average influence of solar activity improved the results considerably. In further work, the team will use data from remote stations to further remove noise from solar activity.

The work suggests “there may be regular detectable changes in the magnetic field which, with further study and isolation, may in fact support the construction of a forecasting system in the future,” Schneider said. .

Reference: “A Decade-long Case-Control Study of California Ground Magnetometers Reveals Modest Signal 24-72 Hours Before Earthquakes” by William D. Heavlin, Karl Kappler, Lusann Yang, Minjie Fan, Jason Hickey, James Lemon, Laura MacLean, Thomas Bleier, Patrick Riley and Daniel Schneider, September 1, 2022, Journal of Geophysical Research: Solid Earth.
DOI: 10.1029/2022JB024109

Interesting facts about earthquakes:

• The largest recorded earthquake in the world was a magnitude of 9.5 (Mw) in Chile on May 22, 1960.
• The largest recorded earthquake in the United States was a magnitude of 9.2 that struck Prince William Sound, Alaska on Good Friday, March 28, 1964,
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• The world’s deadliest recorded earthquake occurred in 1556 in central China. It struck a region where most people lived in caves carved from soft rock. These dwellings collapsed during the earthquake, killing an estimated 830,000 people. In 1976 another deadly earthquake struck in Tangshan, China, where more than 250,000 people were killed.
• The earliest reported earthquake in California was felt in 1769 by the exploring expedition of Gaspar de Portola while the group was camping about 30 miles southeast of Los Angeles.
• It is estimated that there are 500,000 detectable earthquakes in the world each year. 100,000 of those can be felt, and 100 of them cause damage.
• Each year the southern California area has about 10,000 earthquakes. Most of them are so small that they are not felt. Only several hundred are greater than magnitude 3.0, and only about 15-20 are greater than magnitude 4.0. If there is a large earthquake, however, the aftershock sequence will produce many more earthquakes of all magnitudes for many months.