How do scientists measure the strength of an earthquake?

A few different scales measure how strong an earthquake is. The best known is the Richter scale, created in 1935, which uses an instrument called a seismograph to measure the size of the ground waves created by an earthquake.An earthquake’s size, or magnitude, generally ranges from 1 to 8 on the Richter scale (though the waves of some giant quakes have registered well beyond the top of the scale). The shock waves of an earthquake that registers a magnitude of 1 can only be detected with special instruments, while those with a magnitude of 8 cause massive damage.

Every increase of one number means a tenfold increase in the strength of an earthquake; for example, a quake that measures 5 on the scale is 10 times stronger than one that measures 4. Some new methods have been devised to measure earthquakes, including one that measures what is called moment magnitude. This scale examines the size of the fault where the earthquake took place and measures how much Earth’s crust has slipped.

The Mercalli scale is also used to measure the strength of an earthquake. This scale works by describing the effect an earthquake has on people and structures. It lists 12 levels of intensity an earthquake can reach. At level 1, for example, only a few people may feel a quake, but at level 6, it is felt by all and damage starts to occur to buildings. A level 12 earthquake would bring about large-scale destruction.