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12 surprising facts about earthquakes

To mark Quake, a thrilling animated drama set during an earthquake and inspired by the remarkable but little-known world-wide revolution of digital humanitarianism, we've put together some astonishing scientific and historical earthquake facts…

1. There are several million earthquakes annually

According to the United States Geological Survey, there are around 17 major earthquakes measuring above 7.0 on the Richter scale – and one great earthquake measuring above 8.0 – each year. However, experts estimate that there are actually several million earthquakes annually; many go undetected due to their geographical remoteness or small magnitude.

2. An earthquake can affect the length of a day

On 11 March 2011, an 8.9 magnitude earthquake which struck northeast Japan altered the distribution of the earth’s mass, causing it to rotate slightly faster, and shortening an earth day by around 1.8 microseconds.

3. San Francisco is moving towards L.A.

The city of San Francisco is moving toward Los Angeles at the rate of about two inches per year. That's the same pace at which your fingernails grow. This is happening because the two sides of the San Andreas Fault are gradually slipping past one another. The cities will meet in several million years.

Golden Gate Bridge in San Francisco, California, has undergone extensive seismic retrofit work.

4. Standing water smells before an earthquake

Ponds, canals, lakes and other standing water may give off a nasty whiff and become slightly warmer before an earthquake. This is due to gases being released underground as the plates shift. This can contribute to a change in the behavior of wildlife in the area. Scientists from the Department of Life Sciences at the Open University observed toads disappearing before an earthquake which struck Italy in 2009 – and returning afterwards. It is also believed toads detect changes in water chemistry caused by stresses in rocks.

5. Internal waves post-quake are called “seiches”

After an earthquake, you can sometimes see an internal wave sloshing the water about in swimming pools and ponds. This is called a seiche (pronounced “saysh”). The water can continue sloshing about for hours after the end of the earthquake. The swimming pool at the University of Arizona in Tucson lost water from a seiche caused by the 1985 earthquake in Mexico, 2000km away.

6. Inca and traditional Japanese architecture was designed with earthquakes in mind

Inca architecture was built to withstand earthquakes, as are Japanese pagodas.

Over 500 years ago, when Incan workers built the city of Machu Picchu, they devised an ingenious building technique to prevent the structures from collapsing during the country’s frequent earthquakes.

7. The Pacific Ocean is the root of most earthquakes

The vast majority – in fact about 90% – of the world's earthquakes occur along the Ring of Fire, which is an area in the basin of the Pacific Ocean.

8. A Chilean city moved ten feet to the west as a result of an earthquake

During a massive earthquake on Saturday 27 February, 2010, measuring 8.8 on the Richter scale, the earth’s crust was ripped so dramatically that the city of Concepcion actually moved 10 feet to the west.

9. An earthquake caused Everest to shrink

On 25 April 2015, a magnitude 7.8 earthquake inflicted severe damage to the nation of Nepal, causing several Himalayan mountains to shrink, including Mount Everest which shrunk by one inch.

Earth's highest mountain, Mount Everest, is located in the Mahalangur Range.

10. In Japanese mythology earthquakes were caused by a giant catfish

Historically it was believed that Namazu – a giant catfish – which lives submerged in mud under the Japanese islands, was responsible for earthquakes. Many believed that the catfish would thrash about, resulting in seismic activity when Kashima, a god of thunder, was not watching.

The Ancient Greeks believed that Poseidon, the god of the sea, caused earthquakes by banging on the earth with his trident when he was angry. Hindu mythology believes that the earth is held in place by eight elephants, which are in turn balanced on the back of a turtle which is standing on a snake’s coils. Any of those animals moving causes an earthquake.

11. Animals have been observed changing their behaviour prior to an earthquake

It is not just toads which have been observed reacting to seismic activity: before the Indonesian earthquake and tsunami in 2004, witnesses reported seeing animals and birds heading for the higher ground. Scientists think that animals may sense weak tremors before a quake, or possibly electrical signals triggered by the shifting of underground rocks.

Sulfur combusts with air to create astonishing blue lava-like rivers of light in the Kawah Ijen crater on the Indonesian island of Java.

12. A British engineer identified the cause of earthquakes

We have British engineer John Michell to thank for identifying the cause of earthquakes, at the beginning of the 18th Century. He was one of the first fathers of seismology, and he propounded his theory that earthquakes and their resulting waves of energy were caused by “shifting masses of rock miles below the surface”.

Listen to or watch Quake, a thrilling drama set during an earthquake and inspired by the remarkable but little-known world-wide revolution of digital humanitarianism.

Quake from BBC Radio 4