#1027 How do animals sense earthquakes?

How do animals sense earthquakes? No one actually knows how animals can sense earthquakes. They might be able to hear them. Possibly they can smell them. It could be that they sense the changing pressure.

The surface of our planet is constantly moving and there are several hundred earthquakes a day. Many of them are under the sea or where there are no people. The majority of them are also too small for us to sense. There are about 14,000 earthquakes a year. Magnitude 7 earthquakes happen roughly once a month. Magnitude 8 earthquakes happen approximately once a year.

Earthquakes are measured with a magnitude scale. That means each jump in a number if a multiplication of ten times for the power of the earthquake. A magnitude 2 quake is ten times more powerful than a magnitude 1. A magnitude 3 earthquake is 100 times more powerful than a magnitude 1, and so on. For this reason, a magnitude 10 earthquake is practically impossible on earth because no fault line could displace enough ground to create that much seismic energy. The most powerful recorded earthquake was the magnitude 9.5 earthquake in Chile in 1960. It was so powerful that people couldn’t stay on their feet.

There is a CCTV video on YouTube of a dog called Sophie lying on the floor of an office building in Eureka California before a major earthquake strikes. There is a time counter on the video. At 17:21:24, Sophie looks down at the floor then looks up. She turns her head to the sides, as though trying to hear something. At 17:21:35 she raises her right ear and angles her head towards the floor. At 7:21:37, Sophie looks sharply down at the floor again. 1 second later, at 17:21:38, she leaps to her feet and races out of the room. Footage from other rooms show that she was racing to find her owner, who was in another room. Nineteen seconds after Sophie first looked at the floor and 4 seconds after she sprinted out of the room, at 17:21:43, the room starts to shake like crazy. The dog sensed the earthquake nineteen seconds before it struck. How?

There are several theories, but nobody knows for definite. The first theory is that dogs can hear earthquakes long before we can. Dogs have a far superior sense of hearing to ours and they can hear much higher frequencies than we can. Because they can hear higher frequency sounds, they can hear much quitter sounds than we can. The seismic energy moves out from the epicenter of the earthquake and makes the ground vibrate. This produces high frequency sound that travels very quickly through the ground. Sound travels faster through a denser material and the speed of sound in the ground is faster than that of the air. Dogs are better at hearing higher frequency sounds and they are closer to the ground than we are, so it is reasonable to think that they are just hearing the sounds of the earthquake before we do.

The second theory is that they can smell them. In the video, Sophie turns her nose to the floor. Earthquakes break up the ground and a lot of gases are released in the process. These gases can rise to the surface and are released with the quake. Dogs do have a good sense of smell, but being able to smell the gases before they break out of the earth is probably unlikely.

The most probable reason is that they are sensing the P waves. When there is an earthquake, the tectonic plates shift and suddenly move. This energy is released as an energy wave, travelling through the ground. There are two waves that move out. The first wave is called a compressional wave (P wave). The P wave travels very quickly, at a speed of about 6 km per second, depending on the type of rock. The second wave is the shear wave (S wave) and it travels at about 4 km per second. The shear wave is the wave that carries the majority of the energy and causes all of the shaking and damage of the earthquake. The P wave is a pressure wave, but we are usually not sensitive enough to sense it. Dogs are far more sensitive than we are and they can probably detect the pressure difference that comes with the P wave. This is probably what first alerts them and then their other senses give them confirmation. It is probably more a combination of all of these methods than one on their own.

Seismologists have looked at animals to help them design earthquake detectors. Detecting an earthquake 19 seconds before it happens could make a big difference, but detecting it even earlier would be better. Some studies have shown that there are some animals that can detect earthquakes hours before they happen. A study in Italy looked at a range of animals over a six month period and they put accelerometers on them to track their movement. They compared this movement to detected earthquakes and they noticed that many of the animals were changing their behavior at least 20 hours before the earthquakes happened. Somehow, they were able to sense the impending earthquake. The experts thought the animals might be able to detect the changing pressure of the rocks under the earth because the high stress in the rocks strips the electrons off atoms and these ions flow up through the earth, ionizing the air. It is very difficult to test this theory because you need animals and you need to know when there will be earthquakes. And this is what I learned today.

Photo by Doruk Aksel Anıl: https://www.pexels.com/photo/demolished-building-after-earthquake-15823390/

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