When the next major earthquake occurs anywhere in the world, it will arrive without warning, destroying infrastructure and endangering human life.
But days before the event, titanic geological forces will be at work, deforming the crust in subtle ways that could theoretically predict the catastrophe to come.
One possible sign could be a flicker in the magnetic field ebbing and flowing around our planet. For decades, researchers have debated the merits of finding magnetic signatures for upcoming shocks due to a lack of convincing evidence.
A new case-controlled study by QuakeFinder, a humanitarian research project by systems engineering services company Stellar Solutions, in collaboration with the Google Accelerated Science team, concludes there may be good reason to keep searching.
By applying machine learning to ground-based measurements of local magnetic changes ahead of a series of significant earthquakes across California between 2005 and 2019, the researchers found evidence of a pattern that warrants further study.
That’s not to say that the effect they observed could necessarily be used to predict earthquakes, but it’s an intriguing clue for future studies nonetheless.
“We’re not claiming that this signal exists before every earthquake,” QuakeFinder director Dan Schneider told Joshua Rapp Learn at Eos.
But the findings could be enough to keep the controversial topic of electromagnetic predictions of large tremors alive a little longer.
Premises behind hypothetical fluctuations in the magnetic field before earthquakes sound reasonable enough. Some argue that the massive pressure build-up in the crust before an earthquake could theoretically change the properties of the rock strata enough to affect their conductivity.
Other studies suggest that pockets of trapped gas build up prior to release, generating the electrical currents necessary to affect magnetic activity.
Spotting the resulting ultra-low frequency shifts in the magnetic field would alert authorities that something big is about to burst and give them time to prepare in the same way communities might for a growing hurricane.
Unfortunately, what sounds like a promising idea encounters a number of hurdles when it comes to application.
For one thing, many things can create low-frequency wobbles in local areas of a magnetic field. Even an increase in nearby traffic or small shifts in solar activity can produce a hum that could be mistaken for a geological fault.
To untangle a reliable signal from this noise requires accurate measuring equipment at fixed locations near significant vibrations. There, too, enough tremors of the right size must be recorded for a statistical sample.
With research sites near faults throughout the state of California, Quakefinder is well-positioned to overcome these hurdles.
Magnetometers buried at the various research sites provided researchers with a significant amount of data on earthquakes greater than magnitude 4.5.
After selecting quakes for which measurements from two nearby locations were available and excluding pairs from locations without suitable records, the researchers were left with measurements from 19 earthquakes.
This sample was then split into two groups, one serving as the basis of a machine learning study that attempted to extract potential patterns from known influences, while the second group served as a test for possible discoveries.
The signal-to-noise ratio determined by the procedure and confirmed in the test run was not exactly strong. As the researchers concede in their published report, apparent pre-quake electromagnetic anomalies would have been “observed, documented, and accepted much earlier” in previous studies.
But they suggest something intriguing is lurking in the electromagnetic glimmer, like a suspicious scream in a rainstorm that could be present up to three days before an earthquake. Fine-tuning the researchers’ method with a larger sample could potentially identify what’s going on.
Should future studies uncover a reliable hum of impending doom in an area’s magnetic field, it may still not be a universal tune, requiring yet further testing at multiple locations around the world.
For now, the idea of using tiny changes in the planet’s magnetic field to predict tremors remains controversial. But spurred on by results like these, further investigation could finally uncover the secret whispers of a fracture at the fracture site.
This research was published in the Journal of Geophysical Research: Solid Earth.
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