When the next big earthquake hits somewhere around the world, it will arrive without warning, destroying infrastructure and putting lives at risk.
However, for days before the event, titanic geologic forces will already be at work, deforming the crust in subtle ways that could, in theory, predict impending doom.
One possible sign could include flickering in the magnetic field that ebbs and flows around our planet. For decades, researchers have debated the merits of hunting for magnetic signatures in impending tremors, due to a lack of conclusive evidence.
A new case-controlled study from QuakeFinder, a humanitarian research project at systems engineering services company Stellar Solutions, in collaboration with the Google Accelerated Science team, concludes that there may be a good reason to keep looking.
Applying machine learning to ground-based measurements of local magnetic changes leading to a number of major earthquakes in California between 2005 and 2019, the researchers found signs of a pattern that warrants further study.
That doesn’t mean the result they observed could necessarily be used to predict earthquakes, but it’s nonetheless an exciting lead for future study.
“We’re not claiming that this signal exists before every earthquake,” QuakeFinder director Dan Schneider told Joshua Rapp Learn at Eos.
However, the findings could be enough to keep the controversial topic of electromagnetic big-quake predictions alive for a little while longer.
The assumptions behind hypothesized fluctuations in the magnetic field before earthquakes sound reasonable enough. Some argue that the massive buildup of pressure in the crust before an earthquake could, in theory, change the properties of rock layers enough to affect their conductivity.
Other studies hint that pockets of trapped gas build up before being released, creating the necessary electrical currents to affect magnetic activity.
Detecting the resulting ultra-low-frequency shifts in the magnetic field would give authorities a warning that something big is coming, giving them time to prepare the same way communities might for a growing hurricane.
Unfortunately, what sounds like a promising idea runs into a number of obstacles in implementation.
First, many things can create low-frequency oscillations in local patches of a magnetic field. Even increases in nearby motion or small shifts in solar activity can create a hum that can be mistaken for a geological disturbance.
Decoupling a reliable signal from this noise requires accurate measurement equipment at fixed locations near large vibrators. Even where this is the case, enough earthquakes of the right size must be recorded for a statistical sample.
With survey sites located near faults throughout the state of California, Quakefinder is well positioned to overcome these obstacles.
Magnetometers buried at the various survey sites provided the researchers with a fairly large amount of data for earthquakes greater than 4.5 on the Richter scale.
After selecting earthquakes for which measurements were made from two nearby sites, and excluding pairs of sites 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 tease out potential patterns from known influences, with the second group serving as a test for any potential breakthroughs.
The signal-to-noise ratio determined by the procedure and confirmed in the test run was not exactly robust. As the researchers admit in their published report, apparent electromagnetic anomalies before the earthquakes “would have been observed, documented and accepted much earlier” in earlier research.
But they suggest something fascinating lurks in the electromagnetic glow like a suspicious howl in the storm, a howl that could be present up to three days before an earthquake strikes. Fine-tuning the researchers’ method using a larger sample may be able to determine what’s going on.
If future studies come up with a reliable hum of impending doom in a region’s magnetic field, it may not be a universal tune, still requiring further testing at many locations around the world.
For now, the idea of using tiny changes in the planet’s magnetic field to predict tremors remains controversial. But, benefiting from results like these, further investigations could eventually uncover the secret whispers of a breakpoint bug.
This research was published in Journal of Geophysical Research: Solid Earth.