Predicting Earthquakes: Slight Shifts in Magnetic Field Preceded California Quakes

Magnetometers detected faint signals that may improve our understanding of what happens before earthquakes and offer promise for early detection.

Scientists studying intermediate 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 signal of the magnetic field change is faint but statistically significant, and the seismologists hope their technique can be refined to eventually help forecast earthquakes. The research was published recently in the Journal of Geophysical Research: Solid Earth.

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

Debates Over Magnetic Field Changes and Earthquakes

Although it’s always been controversial, the idea that the magnetic field may shift before earthquakes has been around for a while. The U.S. Geological Survey (USGS) states that “despite decades of work, there is no convincing evidence of electromagnetic precursors to earthquakes.”

In collaboration with the Google Accelerated Science team, the scientists tapped into magnetic field data from an array of magnetometers at 125 sensor stations along major faults 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 accounted for other kinds of processes that might affect the magnetometers but have nothing to do with earthquakes, such as rush hour traffic. According to Schneider, differentiating this kind of noise from potential earthquake-related signals is the biggest barrier to interpreting these data. After training their algorithms on half the data set, 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’d like to further hone the models to eliminate more ambient noise from the magnetometers. In this study, for example, accounting for the average influence of solar activity substantially improved the results. In continuing work, the team will use remote station data to further eliminate noise due to solar activity.

The work suggests “there may be regular detectable changes in the magnetic field that with further study and isolation, could actually support the construction of a forecasting 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 Prior 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, 1 September 2022, Journal of Geophysical Research: Solid Earth.
DOI: 10.1029/2022JB024109

Interesting Earthquake Facts:

• The largest recorded earthquake in the world was a magnitude 9.5 (Mw) in Chile on May 22, 1960.
• The largest recorded earthquake in the United States was a magnitude 9.2 that struck Prince William Sound, Alaska on Good Friday, March 28, 1964, UTC.
• 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.

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