How It Works
Earthquake facts

Earthquake facts: 5 things you never knew about earthquakes – video

Earthquake facts

Earthquakes are one of our planet’s most destructive natural hazards, caused by the constant shifting of the tectonic plates as they smash into each other or pull apart. Thanks to some pretty clever scientific equipment we know more about these earth-shattering events than ever before. Here are 5 mind-blowing facts about Earthquakes that you have probably never heard before…

1. Earthquakes can make days shorter

You know those days at work when the end can’t come soon enough? Well get ready to thank the Tohoku earthquake in Japan, because since it occurred in 2011, every day has been 1.8 microseconds shorter. The quake made Earth spin slightly faster by changing its rotation around an imaginary line called the figure axis. The Earth’s mass is balanced around the figure axis, and it wobbles as it spins. That wobble naturally changes one metre a year due to moving glaciers and ocean currents but since the 2011 earthquake the Earth’s wobble has increased by about 17 centimetres.

2. Earthquakes can happen off Earth

We’re not the only ones who suffer the devastating effects of earthquakes, there’s also evidence of ‘marsquakes’ on Mars, vibrations on Venus, movement on many moons of Jupiter, and one of the moons of Saturn – Titan – also shows signs of… tremors. Seismometers on the Moon detected tidal ‘moonquakes’ caused by the pull of the Earth’s gravity, vibrations from meteorite impacts and tremors caused by the Moon’s cold crust warming after the two-week lunar night.

3. Earthquakes used to be recorded using pots

The earliest known seismoscope was invented by a Chinese philosopher in 132 CE. It didn’t actually record ground movements, but simply indicated that an earthquake had hit. The cylindrical vessel had eight dragon heads around the top, facing the eight principal directions of the compass, each with an open-mouthed toad underneath it. Inside the mouth of each dragon was a ball that would drop into the mouth of the toad below when an earthquake occurred. The direction of the shaking could be determined by which dragon released its ball. It is not known what was inside the vessel, but it is thought that some kind of pendulum was used to sense the earthquake and activate the ball in the dragon’s mouth.

4. There are around 500,000 earthquakes every year

Thankfully, most of them are just tiny tremors. Only around 100,000 earthquakes can actually be felt each year, and of those, only 100 or so cause any real damage. Southern California alone has around 10,000 each year, but its thought most of these are caused by overweight tourists hastily taking a much-needed rest.

5. California is overdue a big quake

On the subject of California, the San Andreas Fault extends 1,300 kilometres along its coast, and when it ruptures, it ‘unzips’ along its length. Each section of the fault releases energy – the longer the fault, the more energy released and so the bigger the quake… and the zip, apparently. Scientists believe the San Andreas Fault is overdue for a potential magnitude 8.1 earthquake over a 547-kilometre length. The southern segment has stayed static for more than a century, allowing enormous stresses to build up.

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