Predicting Earthquakes: Slight shifts in the magnetic field preceded the California earthquakes

Magnetometers detected faint signals that could improve our understanding of what happens before earthquakes and offer promising early detection.

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

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

The magnitude 6 earthquake in South Napa, California, in August 2014 broke up the ground in places, including this vineyard. Photo credit: US Geological Survey

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

The researchers searched data from 125 magnetometer sensor stations like this one, located along major faults in California, for signals of magnetic field shifts that occurred before earthquakes. Photo credit: QuakeFinder

Working with the Google Accelerated Science team, the scientists tapped into magnetic field data from a series of magnetometers at 125 sensor stations along major faults in California. They collected data from 2005 to 2019 when 19 earthquakes of magnitude 4.5 or greater occurred on the fault.

Their multistation analysis considered other types of processes that might affect the magnetometers but are unrelated to earthquakes, such as: B. commuter traffic. According to Schneider, distinguishing this type of noise from possible earthquake-related signals is the biggest hurdle in interpreting this data. After training their algorithms on half the dataset, the researchers identified a signal that indicates changes in the magnetic field between 72 and 24 hours before the earthquakes.

Schneider said that in the future he plans to further refine the models to eliminate more ambient noise from the magnetometers. For example, in this study, considering the average influence of solar activity improved the results significantly. In further work, the team will use data from distant stations to further eliminate noise due to solar activity.

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

Reference: “Case-Control Study on a Decade of Ground-Based Magnetometers in California Reveals Modest Signal 24-72 hr Before to 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 the earthquake:

• The world’s largest recorded earthquake had a magnitude of 9.5 (Mw) on May 22, 1960 in Chile.
• The largest recorded earthquake in the United States was a magnitude 9.2 that struck Prince William Sound in 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.