We may be close to being able to predict earthquakes

Lights in the sky and glowing, crackling rocks: the science of Ultra Low Frequency Electromagnetic Waves deep in the Earth

Earthquakes are devastating natural phenomena. The first one recorded in history was around 1831 BC in Mount Tai, China. That country is also the site of the world’s deadliest earthquake in 1556 AD. The earthquake struck in a region where people had carved their homes out of soft rock which then collapsed killing 830,000 people.

The Richter scale measures the intensity of earthquakes logarithmically, meaning that each level on the scale is 10 times more violent than the previous based on the size of the waves recorded on a seismometer, a device for measuring earthquakes.

Seismometer. Yamaguchi先生 Creative Commons Attribution-Share Alike 3.0 Unported

In terms of seismic energy released, the increase is even more with each level. The amount of energy released in a magnitude 8.0 quake, for example, is 1000 times the nuclear bomb dropped on Hiroshima, Japan while a magnitude 9.0 quake is 30,000 times. And these numbers only account for seismic energy, meaning the energy that causes the earth to quake. A great deal more energy goes into heating or thrusting rocks upward.

One of the worst aspects of earthquakes is that they are unpredictable. Unlike other natural disasters such as hurricanes, tornadoes, tsunamis, and even volcanic eruptions, we only know an earthquake is about to strike when the earth starts shaking, and by then it is often too late.

That doesn’t mean, however, that earthquakes are completely sudden. It is just that we can’t see what is going on beneath the Earth, where forces may be building kilometers down.

Earthquakes happen because the rocks under our feet, deep within the earth, are in constant motion. This is thanks to the molten core that retains its heat from the Earth’s formation 4.5 billion years ago. Rocks within the Earth’s upper crust press against one another. At typical temperatures of 300-400 degrees, the rocks first deform in an elastic way, meaning that, the rocks will return to their original shape if the forces are removed, and then in a plastic way, where the rocks retain the deformed shape. As they press into one another, they also form cracks and break apart. Eventually the pressure is released, causing an earthquake.

All of this building stress and pressure is detectable in the form of electromagnetic fields which can begin days or weeks prior to an earthquake. These fields were first documented prior to two earthquakes in the late 1980s: the Loma Prieta, Central California on October 17, 1989 (magnitude M=7.1) and Spitak, Armenia, on December 7, 1988 (M=6.9). The fields appeared and increased 3-5 days before the Spitak and 12 days before the Loma Prieta earthquakes. Since that time, they have been documented at several more, primarily within about 100 km of an epicenter. Prior to a particularly powerful 8.0 magnitude earthquake in Guam in 1993, these were observed as far as a month prior to the event.

These large scale, Ultra Low Frequency Electro-Magnetic (ULFEM) field anomalies generate tremendous currents which can cause rocks on the surface to glow and crackle with electricity and light to appear in the sky. Powerlines have been known to arc with these releases of energy as well. Although there remains some doubt about the reality of these phenomena, in general, it is agreed that some electromagnetic waves do emanate from the earth prior to an earthquake.

Photograph by Mr. Kuribayashi, Reprinted with permission from Seismological Research Letters || https://pubs.geoscienceworld.org/ssa/bssa/article-abstract/63/6-1/2177/117338/earthquake-lights-a-review-of-observations-and?redirectedFrom=fulltext

One theory is that these are generated from the motion of conductive rocks in the Earth’s magnetic field. As cracks form under the earth around the epicenter, electromagnetic micro-fields combine, oriented according to the Earth’s own magnetic field.

This theory suggests that the rocks act much like the coils of wire in a generator. The coils of wire move near a magnet (or vice versa) which then induces a current in the wire by the laws of electromagnetism.

A competing theory is that the electricity arises from a piezoelectric effect, which means that quartz crystals under the Earth accumulate a charge from their motion. Some microphones work by a similar phenomena where the sound deforms their shape and that mechanical energy is converted into an electrical signal.

A third, more recent, theory, developed by NASA researchers, is based on solid state physics. Solid state physics is responsible for a lot of the technology we use from microprocessors to harddrives to memory as well as lasers and light emitting diodes.

Electrical currents can be manipulated within solid, non-moving materials using the properties of materials. Without solid state physics, we would still be using vacuum tube computers.

The theory is that rocks in the Earth’s crust contain positively charged chemical compounds such as Magnesium Oxide, which can, under stress, activate and carry charge.

These rocks, when subject to compressive forces, release charge carriers which flow out of the rocks at high speed. As rocks become heavily loaded with stress and heat, these currents increase creating electricity.

Experimentalists at NASA put a kind of igneous rock called gabbros under a hydraulic press in a Faraday cage, to avoid external electrical influences, and showed an instant small current. Under constant load, this current decayed over time, showing that the gabbros was releasing its charge.

A similar effect was found when dropping the rocks from a high tower. The charge would tend to flow from the stressed part of the rock to the non-stressed parts. That turned out to be the key. When rocks are uniformly stressed, there is no gradient and no flow of current, but, when they are stressed in one area, there is a flow, almost like squeezing a balloon in one spot causing it to bulge elsewhere.

Thus, applying stress to the rocks activated previously dormant charge carriers. This creates electromagnetic waves.

The flow may be why some animals act strangely before an earthquake. They might be detecting the ULFEM waves emanating from the rocks beneath. In particular, animals such as some birds and turtles, which can detect the Earth’s magnetic field, could respond to the variations in magnetism that come with electrical currents. Ruminant animals like deer and cows also tend to align their bodies north-south and may be disrupted from low frequency magnetic fields.

The big question, given all this happens days before an earthquake, is whether these phenomena can be used to predict earthquakes and save lives. The short answer is probably but not yet.

California has been monitoring telluric (meaning “from the Earth”) ULFEM fields using the Stanford-USGS array and an array maintained by QuakeFinder.com in the hopes that they can predict earthquakes before they happen.

The biggest problem with detecting these waves is that they are very low power and there are much stronger signals from the ionosphere and magnetosphere high above us as well as from human activity: powerlines, homes, and so on. This makes it a big data analysis problem.

This isn’t the first time it has been tried either, with little success. An array of 80 stations along the San Andreas fault line of proton-precession magnetometers was built in 1972 to monitor ULFEM waves. It operated until 2002. In all those 30 years, they detected only a single magnetic precursor to a 5.1 magnitude earthquake.

New technology may be the answer, however, with more sensitive, three-component (meaning they measure all three components of the magnetic field, not just the magnitude) magnetometers that can tell us not only the size but also the direction of the magnetic field lines.

So far, however, any detection of ULFEM pulses prior to earthquakes along the San Andreas fault line has been suspiciously correlated with the day/night cycle suggesting that they are not tectonic in origin, perhaps relating instead to human activity.

Others have suggested the problem is in the data analysis tools and that machine learning may bring the biggest breakthrough. A study of the data from the USGS magnetometer array trained a model based on Linear Discriminant Analysis (LDA) and found a “modest” signal 24-72 hours prior to an earthquake.

While LDA is a relatively old statistical analysis method, it may be that more advanced AI techniques could sift the tectonic ULFEM results from the other origins and signal an earthquake early enough and with enough accuracy to provide a warning. Even 20 minutes before the shaking starts would be worth something.

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Freund, Friedemann T., and Minoru M. Freund. "Paradox of peroxy defects and positive holes in rocks. Part I: Effect of temperature." Journal of Asian Earth Sciences 114 (2015): 373-383.

Scoville, John, Jaufray Sornette, and Friedemann T. Freund. "Paradox of peroxy defects and positive holes in rocks Part II: Outflow of electric currents from stressed rocks." Journal of Asian Earth Sciences 114 (2015): 338-351.

Wang, Can, et al. "Assessment of a claimed ultra-low frequency electromagnetic (ULFEM) earthquake precursor." Geophysical Journal International 229.3 (2022): 2081-2095.

Heavlin, William D., et al. "Case‐Control Study on a Decade of Ground‐Based Magnetometers in California Reveals Modest Signal 24–72 hr Prior to Earthquakes." Journal of Geophysical Research: Solid Earth 127.10 (2022): e2022JB024109.