# How Do We Measure an Earthquake?

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## Seismographs

• A seismograph uses a type of pendulum that records the tremors made by an earthquake. Seismographs are usually positioned about 62 miles (100 kilometers) from an earthquake's general epicenter, which is the location on the Earth's surface directly above the original movement. Using the Richter Scale, the seismograph recordings are used to measure the earthquake. There is also another recording system, originally developed by Giuseppe Mercalli.

## Richter Scale

• The Richter scale uses seismograph waves to record the magnitude of an earthquake. Using a complicated mathematic system originally designed by Charles Richter, the wave with the highest amplitude recorded is used to measure the quake's magnitude, and a number is given to the quake based on what that highest amplitude was. The Richter Scale uses a base 10 system, or logarythmic system. This means that an earthquake measuring a five on this scale was 10 times stronger than a quake measuring a four. Most earthquakes measure at a two and are barely felt by people. It is believed to be impossible for an earthquake to measure much past a nine, because there isn't a fault on the Earth big enough.

## Mercalli Scale

• The Mercalli Scale is much less scientific than the Richter scale, because it uses human observation and visual effect to record the quake's intensity. The Mercalli Scale uses a Roman numeral system to record a quake based on the number of people in an area that felt the quake and any noticeable damage. An earthquake that is felt by everyone in the area is measured at a VI, which is about the equivalent of a five on the Richter Scale. A measure of I can be between a one to two on the Richter Scale and is barely noticeable. The highest Mercalli measurement is XII, which is equal to a Richter measurement of eight or greater and involves excessive damage and visible waves on the ground.

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