Signs Before an Earthquake: Facts and Myths
Many cultures share stories about warning signs before earthquakes: still, hot weather, strange clouds, glowing skies or restless animals. These ideas are memorable, and some of them are connected to real, if poorly understood, effects. The problem is that none of them reliably shows up before earthquakes and only before earthquakes.
This article goes through the most common claimed signs one by one, explains what science actually knows about each, and ends with a myth-versus-fact table you can share.
Quick answer
There is no known sign that reliably warns of an earthquake in advance. Hot or still weather, quake clouds and pet behavior have no proven link to coming earthquakes. Some effects, such as foreshocks, radon changes and earthquake lights, have been reported before some quakes, but they are inconsistent, and foreshocks can only be recognized after the larger quake happens.
Earthquake weather
A popular belief holds that earthquakes come on hot, calm, muggy days. The USGS says there is no such thing as earthquake weather. Earthquakes begin miles below the surface, far beyond the reach of air temperature, wind or rain. They happen in every season, in every kind of weather and at every time of day.
The belief likely persists because people remember the weather on the day of a frightening event. If a big quake happened on a hot day, that day sticks in memory, while the many hot days with no earthquake are forgotten.
Earthquake clouds
Photos of long, straight or oddly shaped clouds are often shared online as earthquake clouds. There is no scientific evidence that clouds can signal a coming earthquake. Unusual cloud shapes come from normal weather processes such as wind shear, mountain waves and aircraft contrails, and they appear all the time without any earthquake following.
Earthquake lights
Earthquake lights are flashes or glows in the sky that people have reported during, and occasionally shortly before, some earthquakes. Unlike quake clouds, they have a long history of eyewitness reports and some photos and video. Scientists have proposed several possible causes, but there is no agreed explanation.
Some flashes reported during shaking are actually electrical equipment, such as power lines or transformers, arcing as they are shaken. Because earthquake lights are rare, hard to verify and usually seen during the shaking itself, they are not useful as a warning.
Radon gas and groundwater changes
Radon is a radioactive gas that seeps naturally from rocks and soil. Changes in radon levels, and in the level or chemistry of well water, have been reported before some earthquakes. Researchers have studied these signals for decades because they make physical sense: stressed rock can crack and release gas or change how water flows.
The difficulty is that radon and groundwater also change for many ordinary reasons, including rainfall, air pressure and pumping. In many cases a change appears with no earthquake, or an earthquake happens with no change. So far, no one has shown that these measurements can reliably warn of a quake.
Foreshocks: real, but only clear in hindsight
Foreshocks are the one warning sign that definitely exists. Some large earthquakes are preceded by smaller earthquakes in the same place. However, most large earthquakes have no obvious foreshocks, and at the time it happens, a foreshock looks just like any other small earthquake.
A small quake only gets labeled a foreshock after a larger one follows. According to the USGS, roughly 5 percent of earthquakes are followed by a larger one nearby. That is why a small quake raises the chance of a bigger one slightly for a short time, but most small quakes are not followed by anything larger. See foreshock vs aftershock for more.
Unusual animal behavior
Stories of animals acting strangely before earthquakes go back thousands of years. Animals can sense the first, faint P-waves of an earthquake that has already started, a few seconds before people feel the stronger shaking. That is a real effect but not a prediction. Claims of days or weeks of warning rest mostly on stories gathered after the event. Our article do animals predict earthquakes? looks at this in detail.
Do small earthquakes relieve pressure?
Many people hope that lots of small earthquakes release stress and make a big one less likely. Unfortunately, the numbers do not work. The Magnitude scale is logarithmic: each whole step up releases roughly 32 times more energy. It would take about 32 magnitude 5 quakes, or about 1,000 magnitude 4 quakes, to release the energy of a single magnitude 6.
Small earthquakes are simply far too small to drain the stress that builds up for a large one. They are a normal sign of an active area, not a safety valve.
Myth vs fact at a glance
This summary reflects the current scientific view from the USGS and other earthquake agencies.
| Claim | What science says |
|---|---|
| Hot, still weather means a quake is coming | Myth. Weather has no known link to when earthquakes occur. |
| Strange clouds are quake clouds | Myth. Cloud shapes come from normal weather processes. |
| Earthquake lights happen | Reported and possibly real, but rare and not useful as a warning. |
| Radon or well water changes warn of quakes | Studied for decades; changes are inconsistent and not reliable. |
| Foreshocks warn of big quakes | Real, but most big quakes have none, and they are only identified afterward. |
| Animals sense quakes days ahead | Not supported. Animals may react to P-waves seconds before strong shaking. |
| Small quakes prevent big ones | Myth. They release far too little energy. |
Frequently asked questions
Is there any way to tell an earthquake is about to happen?
Not reliably. The closest thing is earthquake early warning, which detects a quake that has already started and can alert you seconds before strong shaking arrives. It is available in some regions, including the U.S. West Coast through ShakeAlert.
Should I worry after a small earthquake near me?
A small quake raises the chance of another quake nearby slightly for a few days, but most are not followed by anything larger. It is a good reminder to check your supplies and review Drop, Cover and Hold On.
Why do earthquake myths spread so easily?
People remember striking coincidences and forget the many times a so-called sign appeared with no earthquake. Photos of odd clouds or posts about pets are also easy to share without checking.
Do earthquakes happen more at certain times of day?
No. Earthquakes occur at all hours. It can seem like they happen more at night because quiet surroundings make small quakes easier to notice.
Key takeaway
No sign reliably warns of an earthquake. Weather, clouds and the idea that small quakes relieve pressure are myths; foreshocks, radon and earthquake lights are real topics of study but cannot be used as warnings. Preparation, not watching for signs, is what keeps people safe.
Sources
- Can you predict earthquakes? — U.S. Geological Survey
- Earthquake Hazards Program — U.S. Geological Survey
- Earthquake Country Alliance — Earthquake Country Alliance