Saturday, January 29, 2022

Can animals sense earthquakes?

[This is a transcript of the video embedded below. Some of the explanations may not make sense without the animations in the video. References are in the info fold below the video on YouTube or on Patreon.]

Earthquakes are much more common than you might expect. An earthquake of magnitude 6 and up happens every couple of days somewhere on the planet. It’s just that most of them don’t affect densely populated areas, and, as the seismologist Nicholas Ambraseys put it “earthquakes don’t kill people, buildings do”.

But earthquakes are the most fatal natural disasters. In the two decades from 1998 to 2017, they killed more than 700 thousand people.

So what are seismologists doing to warn people of earthquakes? Can animals sense if an earthquake is coming? And what are earthquake lights? That’s what we will talk about today.

This is the second part of a two-part video. Last week, we talked about long-term and mid-term predictions for earthquakes. Today we will talk about short-term predictions, that’s months to seconds before an earthquake. Short-term predictions don’t help with infrastructure investments, but they give people time to evacuate.

The one reliable known precursor for earthquakes is the P wave that comes a few seconds up to a minute before the biggest shake. The P stands for primary and for pressure. It’s a longitudinal deformation that travels through earth, so the displacement that the wave produces is parallel to the direction of propagation of the wave.

This P wave is difficult to notice and doesn’t normally cause much damage but it’s fairly easily to measure, so it can be used to issue a warning. What causes most of the damage is the S wave which comes a little later because it travels a little slower. The S stands for secondary or shear. The displacement of this wave is perpendicular to the direction of propagation of the wave, and that’s what causes buildings to crack.

Now strictly speaking using the P wave isn’t a prediction of an earthquake because with the P wave the earthquake has already started. And a few seconds might just be enough to get out of the house, but this will only work if people are alert to the warning to begin with. Clearly you’d want to know at least a few hours or better days ahead if an earthquake is coming up. You want an actual prediction. The most obvious thing you can do for that is to look at records of past earthquakes and see if you can find any precursors in those. The problem is that the known precursors are unreliable.

Take for example the first earthquake with a successful prediction on record: The 1975 Haicheng earthquake in northeast China. It had a magnitude of 7 point 3. The event was preceded by many different precursors: foreshocks, ground-water changes, and strange animal behavior. Seismologists put out a warning on the day of the earthquake before it hit. Buildings in the city were mostly evacuated. About a thousand people died, which for city of that size and an earthquake of that magnitude isn’t much.

Seismologists were really excited about this success. But only a year later, an earthquake of magnitude seven point seven happened just 200 kilometers southwest of Haicheng. No precursors were detected, no warning was issued. The earthquake largely destroyed the city of Tangshan and killed more than a quarter of a million people. That’s the official number. The unofficial number is about three times as high.

As you see, it’s difficult. Seismologists can’t always find precursors, but they have made progress in identifying some of them.

The most obvious precursors are seismic changes like tiny earthquakes or measurable deformations in the rocks. Small deformations in rocks can also allow gases to escape from underground. That’s mainly radon gas which is quite easy to measure since it’s radioactive. Small cracks in rocks can also cause changes in groundwater level. And in case the groundwater is connected to a thermal source, that can further change the ground temperature.

This may all sound rather obvious, but there are also some surprising precursors and not all of them are well understood, like fluctuations of the Earth’s magnetic field. These were measured for example in October 1989, when an earthquake of magnitude 7.1 hit Loma Prieta in Northern California.

Researchers from Stanford University measured fluctuations in the magnetic field first a couple of weeks and then some hours before the earthquake. They only found this in the data after the earthquake had happened, so they couldn’t issue a warning, but the same has also been seen in a few other events so it’s worth monitoring. It’s somewhat unclear at the moment what causes these fluctuations of the magnetic field, could be stress in the rocks, or changes in the flow of molten rocks further underneath.

Maybe related to this or maybe not, sometimes earthquakes are preceded by fluctuations in the ionosphere, so that’s the upper part of the atmosphere at 50 kilometers and up.

For example, two hours before a magnitude 9.2 earthquake hit Alaska in 1964, researchers in Boulder, Colorado, reported a strong anomaly in the ionosphere in that area. This Alaska earthquake, by the way, was the second largest one ever recorded. The largest one is the Valdivia earthquake from 1960 in southern Chile, which had a magnitude of 9.4.

Another electromagnetic phenomenon that researchers have observed are changes in the Van Allen belts. The Van Allen belts are regions in the upper atmosphere where charged particles get trapped by Earth's magnetic field. When those belts become overloaded with too many particles, then some particles hit the upper atmosphere and cause auroras.

Scientists have known since the late 1980s that the van Allen belts change locally in the area of an earthquake several days to several hours before the earthquake hits. In 2003 and 2005 Russian and Italian researchers did a statistical analysis of satellite data and found that particle bursts from the Van Allen belts precede earthquakes by 4-5 hours. They say the correlation has a high statistical significance of 5 sigma.

In 2013, another Italian team found a similar correlation, and they claim an even higher statistical significance of 5.7 sigma. However, the authors also point out that they saw this only for a few earthquakes of magnitude 5 and up. Then again, this may just be because the data aren’t good enough. The Chinese-Italian satellite mission CSES is currently collecting data to maybe solve this puzzle.

So as you can see there are quite a few earthquake precursors that are fairly well established, though not all are well understood. Now what’s with the idea that animals can tell when an earthquake is coming up?

Indeed, that animals act weird before an earthquake has been reported for as long as there’ve been reports, basically. Already in the third century, the Roman author Claudius Aelianus wrote about an earthquake that had wiped out the Greek city of Helike about 400 years BC.

“For five days before Helike disappeared all the mice and martens and snakes and centipedes and beetles and every other creature of that kind in the town left... And the people of Helike seeing this happening were filled with amazement, but were unable to guess the reason. But after the aforesaid creatures had departed, an earthquake occurred in the night; the town collapsed; an immense wave poured over it, and Helike disappeared”.

Makes you wonder how he would have known what the mice and beetles were doing in Greece 500 years before he was born. Also, some recent historical studies showed that coins were still issued in Helike some decades after it allegedly disappeared, there’s no report of Helike’s destruction in Greek texts, and no evidence of a tidal wave washing over the city. So, well. Don’t believe everything you read in thousand years old books, even if it’s in Latin.

But in any case, this is the first anecdote we have of animals acting weird before an earthquake. Such stories frequently made headlines. For example, just a couple of months ago, after an earthquake in Victoria in Australia, zoo staff reported that birds and kangaroos had been acting strangely that day.

And those stories aren’t entirely implausible because animals might be able to pick up some of the previously listed precursors, such as unusual gas emissions or changes to the magnetic field. But as we discussed in a previous video, humans have a tendency to see patterns even where there aren’t any, so going by anecdotes is not a good idea. The major issue with those reports is the lack of control groups. If a herd of sheep acts funny but no earthquake happens, no one writes headlines about that.

But some scientists have looked into the idea that animals can tell when an earthquake is coming up. Already in 1988, Rand Schaal, a geologist from University of California in Davis, did a statistical analysis to test whether the number of newspaper ads about lost pets was a sign of an imminent earthquake. He compared more than 42 thousand reports of missing pets with the times of about 200 earthquakes of magnitude 2.5 or larger in the San Francisco Bay area. He found no significant correlation.

More recently, in 2018, a paper by a group from the German Research Centre for Geosciences analyzed more than 700 reports of claimed correlations between earthquakes and “anomalies” in animal behavior.

Those reports were from more than one hundred different species – fish, mice, elephants, cows, snakes and various pets. The researchers found that the number of claimed observations increases close to the seismic event. Almost 60% of reports come from the last 5 min. This makes it possible that the animals might be detecting the P-wave, which humans usually fail to notice. But 50% of the reports related to only 3 earthquakes and the details of the reports are insufficient for a rigorous scientific analysis. The German group concludes that… they can’t conclude anything because the data is rubbish. So, more work is needed, basically.

Now let’s talked about the mysterious earthquake lights. Some people claim to have seen strange lights in the sky before, during, or shortly after large earthquakes, up to several kilometers away from the epicenter. The lights typically last a fraction of a second to several seconds. Anecdotes about this can be found already in ancient Egyptian, Chinese, and Japanese documents. Those earthquake lights are definitely a real thing. Indeed, you can see them yourself in this video. This footage was captured by security camera at the university in San Miguel, Peru during a 2007 Earthquake. It had a magnitude of 8.

The researchers who captured this video were later able to directly compare it with the recorded seismic activity. In a paper published in 2011 they showed that the time of the lights not only coincided with the time of the earthquakes but that they coincided with peaks of ground acceleration as you can see in this graph.

Earthquake lights have been reported mostly for a certain type of earthquake, the so-called shallow earthquakes of high magnitude. Some of the reports are probably something else, like sparks in electricity lines, but earthquake lights seem to be a real thing. It is not presently well understood what causes those lights, but one hypothesis that seismologists are investigating is piezoelectricity, so that is an electric response that some solid materials have to stress. However, some of the observed earthquake lights last too long for that explanation to work, so that’s probably not the full story.

As you see, seismologists know quite a few precursors, so how is it that still so few earthquakes can be predicted. Researchers from Japan have pointed out that short-term precursors are mostly non-seismic, so understanding and making use of them requires a multi-disciplinary effort that’s slow to get going. Artificial Intelligence will probably help, but big earthquakes are too infrequent for substantial software training, so that won’t really solve the problem.

Another issue is that predictions come with a heavy burden if they’re wrong. A prominent example is the 2009 L’Aquila Earthquake in Italy. It had magnitude 6 point 3. 308 people died. In 2012 a court gave multiple manslaughter convictions to six Italian seismologists for false assurances and failing to predict the earthquake. The conviction was overturned two years later but still Italians yelled “Shame! Shame!” at the scientists.

Well, it’s a shame indeed, but not because the seismologists were wrong. No prediction is ever 100% certain. But it would be good if earthquake predictions would come with a quantitative risk assessment, much like weather forecasts maybe. As you can see, earthquake prediction is a very active research area, and we will update you from time to time. So if you liked this video, don’t forget to subscribe.

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