Small changes in the magnetic field preceded the California earthquakes

Seismological Earthquake Chart
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Seismological Earthquake Chart

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

Magnetometers have detected weak signals that could improve our understanding of what happens before an earthquake and may hold promise for early detection.

Scientists studying moderate 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 magnetic field change signal was weak but statistically significant, and seismologists hope their technique can eventually be improved to help predict earthquakes. The study was recently published Journal of Geophysical Research: Solid Earth.

“It’s a modest signal,” said study co-author Dan Schneider. is the director QuakeFinder, the earthquake research department at Stellar Solutions, a systems engineering services company. “We’re not claiming that this signal precedes every earthquake, but it’s very interesting.”

Vineyard South Napa Earthquake

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

Although always controversial, there is an idea that the magnetic field can change before earthquakes been around for a while. US Geological Survey (USGS) you that “despite decades of work, there is no convincing evidence for electromagnetic precursors to earthquakes.”

Magnetometer Sensor Station

The researchers searched data from 125 such magnetometer sensor stations located along major faults in California for signals of magnetic field shifts that preceded earthquakes. Credit: QuakeFinder

Together with the Google Accelerated Science team, the scientists tapped 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 fault.

Their multi-station analysis took into account other processes that may affect magnetometers but have nothing to do with earthquakes, such as rush-hour traffic. Distinguishing such noise from potential earthquake-related signals is the biggest obstacle to interpreting this data, according to Schneider. After training their algorithm on half of the data set, the researchers identified a signal indicating changes in the magnetic field 72 and 24 hours before the earthquakes.

In the future, Schneider said he would like to further improve the models to remove more ambient noise from the magnetometers. In this study, for example, accounting for the moderate effect of solar activity significantly improved the results. In ongoing work, the team will use remote station data to further remove noise due to solar activity.

The work “may be regular detectable changes in the magnetic field that, with more research and isolation, could really support building a forecasting system in the future,” Schneider said.

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

Interesting earthquake facts:

  • The largest earthquake recorded in the world was on May 22, 1960 in Chile with a magnitude of 9.5 (Mw).
  • The largest earthquake ever recorded in the United States occurred on Good Friday, March 28, 1964, with a magnitude of 9.2 in Prince William Sound, Alaska.[{” attribute=””>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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