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It was so powerful it slightly shortened the length of a day and nudged the Earth on its axis.

The same horseshoe-shaped belt is home to roughly three-quarters of the planet’s active volcanoes.

About 100,000 of them can be felt, and only around 100 cause damage.

Most are below magnitude 2 and are only picked up by sensitive instruments.

But early-warning systems can give you seconds to a minute of notice once one has started - enough to drop, cover and hold on.

A magnitude 9 quake unleashes roughly 1,000 times the energy of a magnitude 7.

The magnitude 9.0 Tohoku quake also dropped parts of the coastline by up to a meter.

An estimated 830,000 people died, many in collapsing cave homes carved into soft rock.

Over millions of years that adds up to hundreds of kilometers of movement.

Early-warning systems detect the harmless P-waves and race out an alert before the strong shaking hits.

Apollo astronauts left seismometers on the Moon, and NASA’s InSight lander recorded thousands of quakes on Mars.

Occasionally what looked like the main quake turns out to be a foreshock of something larger.

Filling large reservoirs and injecting wastewater deep underground have both set off quakes.

In deep water the waves can travel as fast as a jet airliner.