Researchers studying intermediate and large earthquakes have found detectable changes in the local magnetic field that occur 2-3 days before California earthquakes.

In a study published in Journal of Geophysical Research: Solid EarthWilliam Heavlin and his team found that the signal of the magnetic field change is weak but statistically significant, and seismologists hope their technique can be refined to ultimately improve earthquake forecasting.

“It’s a modest signal,” said Dan Schneider, 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,” said Schneider, co-author of the study, “but it’s very interesting.”

California earthquakes ‘predicted’ by changing magnetic field

The idea that the magnetic field can change before California earthquakes has been around for a while, but it’s always been controversial. The US Geological Survey 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 researchers accessed magnetic field data from an array of magnetometers at 125 sensor stations located along major faults in California. They collected data from 2005 to 2019, during which time 19 earthquakes of magnitude 4.5 or greater occurred.

Their multi-station analysis also took into account other types of processes that could affect magnetometers but have nothing to do with earthquakes, such as rush hour traffic. Differentiating this type of noise from potentially earthquake-related signals is the biggest barrier to interpreting this data, Schneider said.

The study could lead to better earthquake forecasting

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 an earthquake, writes

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

The paper suggests that “there may be regular detectable changes in the magnetic field that, with further study and isolation, could support building a forecast system in the future,” Schneider said.

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