Lori Dengler | Share your stories about earthquake anomalies – Times-Standard

Earthquakes cause fault rupture, ground displacement, strong shaking, and tsunamis. These are all fairly well understood phenomena. But there are other things associated with earthquakes that have not been well studied. I call these earthquakes anomalies, and if you've experienced any, I'd love to hear your stories. I have an ulterior motive in asking for your feedback. I am co-conducting a session at the annual meeting of the Seismological Society of America next spring on “Interesting Seismic Observations,” and your reports will provide material for my presentation.

Let's start with the often-mentioned oddity: earthquake lights. These include glowing skies and unusual bursts of light that appear to be closely linked to earthquake vibrations. I first became aware of this phenomenon in April 1992 when several people reported lights after two strong nighttime tremors in the Cape Mendocino earthquakes. The main tremor of magnitude 7.2 occurred in bright daylight, but aftershocks of magnitude 6.5 and 6.6 occurred in the early morning hours of April 26, 1992.

In the days and weeks after the 1992 earthquakes, I talked to many people about their experiences, and when it came to nighttime aftershocks, they often mentioned seeing lights. Some reported bright flashes of blue and white light, like a giant, old-fashioned camera bulb exploding. These flashes are bright enough to be seen in broad daylight, and are caused by arcing electrical lines and exploding transformers.

Many of the 1992 reports were from remote areas where there were no transformers to detonate. The bluish-white color was not the only color observed. The night was clear, the electricity was out, and some people chose to sleep outside due to the numerous aftershocks. Several described a green-yellow glow traveling across the sky that appeared to coincide with the passage of seismic waves.

Seismic waves in the air? Earthquakes are caused by rocks rupturing miles below the Earth's surface, generating seismic waves that travel in all directions. P waves are essentially sound waves that push and pull matter as they travel. In a large earthquake, when those waves reach the Earth's surface, they transmit some of the pushing and pulling motion into the air. P wave oscillations in the atmosphere can trigger visible electrical phenomena. Satellites have detected ionospheric disturbances more than 100 miles above Earth's surface immediately after earthquakes powerful enough to temporarily disrupt communications.

Seismic lights or scintillation may also be caused by pressure changes in rocks as seismic waves travel beneath the surface. Quartz is one of the most common minerals in crustal rocks. When stressed in laboratory experiments, quartz exhibits piezoelectric effects, changing its electrical state, emitting electrons and ions and sending currents to the surface and into the air.

The green glow wasn't the only unusual glow in 1992. A woman in Ferndale described a glowing orange bubble streaming from her backyard during the shaking. Some people saw bursts of orange glow in the distance. The most bizarre description came from a fisherman many miles off the coast that night. M6.5 and 6.6 aftershocks were felt. P waves travel in water as well as air, and he said it felt like the boat had suddenly dropped a foot or two. Then the water began to glow. The glow increased until after a few minutes, he was in the middle of a glowing ocean of water. The glow lasted for more than an hour before it slowly began to fade.

I argue that the orange colors could be the result of thermoluminescence, visible light emitted due to heating. We know that there were several landslides in 1992, and when the slopes collapse, there is intense friction on the surface of the slide. Laboratory studies have replicated the red glows, sometimes called landslide lights. Glowing water has a different source. Light is emitted by a number of living organisms. Some algae and bacteria emit a bluish-green light when they are moved by waves. It is not a stretch to think that seismic vibrations could have a similar effect.

In 1992, another oddity was seeing the Earth visibly rolling. The main shock of 1992 occurred at 11:05 a.m. on a Saturday when many people were outside. Some people reported seeing the land moving like “waves in the ocean.” I became more interested in observations of ground rolling while studying the M6.5 earthquake that occurred on December 21, 1954. Almost everyone who was outside during the earthquake described shaking on the ground. Someone inside saw their hallway go up and down.

Ground rolling has not been taken seriously in the world of seismology for many years. In the 19th and early 20th centuries, it was considered an indicator of very strong ground shaking and was included in the original descriptions of the modified Mercalli scale. But many recent seismologists have thought it was no longer interesting or even a figment of the imagination, and I haven't seen any research papers on the subject in the past half century. I think it's time to take a closer look.

We have had several earthquakes on the North Coast, and I am aware of only two with clear reports of ground fluctuations. Our most recent major earthquake was just over a year ago. The M7.0 Mendocino fault earthquake occurred at 10:44 a.m. when many people were outside. People described trees swaying and roaring but no one mentioned seeing the ground rolling. The 2024 earthquake was a strike-slip earthquake where the fault slip was strictly horizontal. The main shock of 1992 and the 1954 earthquakes were shallow earthquakes that occurred on thrust faults where rocks on one side were pushed up and over rocks on the other side. I think the type of error may matter.

Other earthquakes in the world have produced eyewitness accounts of seeing the ground roll. One of my good friends was outside on October 17, 1989, and saw ripples on the Earth's surface during the M6.9 Loma Prieta earthquake. This earthquake also had a large portion of thrust faulting. My current working hypothesis is that the depth and type of crack matters. Unfortunately, ground rolling observations have not been included in earthquake catalogs for over half a century and I have difficulty pulling up a list of other earthquakes that have produced visible ground ripples.

Sounds are also on the list of earthquake oddities. There are many different sounds associated with earthquakes. My first experience with the North Coast earthquake was in the early morning hours of November 8, 1980, when the shattering of our old clock occurred almost simultaneously with the violent shaking that caused our entire house to groan. It's not just dropping items that produce earthquake sounds. The same P waves that may trigger seismic lights can also produce a low audible roar that some have described as that of an approaching train.

Even gentle P wave action can lead to another generally unpleasant earthquake effect. Nearly 20% of people report feeling nauseous or dizzy during a large-scale earthquake. Blame your inner ear, which senses those movements and is out of sync with what your eyes see. It's the same cause of seasickness, where your body interprets the mismatch as something toxic in your gut.

I've heard of strange smells before, during, or after earthquakes, headaches, wells that suddenly run dry or overflow, and rivers that flow backwards. If you have any of these weird ones up your sleeve or ones I haven't heard of, you can let me know via the email link or phone message line below.

Lori Dengler is professor emeritus of geology at Cal Poly Humboldt and an expert in tsunami and earthquake hazards. Questions or comments about this column, or want a free copy of the “Living on Shaky Ground” preparedness magazine? Leave a message at 707-826-6019 or email [email protected].

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