A seismometer is what earthquakes are commonly measured with. We can define a seismometer as something that converts wave energy into a magnitude on a logarithmic scale.

The information gathered by the seismometer is used for the Richter scale and the moment magnitude scale. The Richter scale is a scale the magnitude of an earthquake is measured on.

The next lesson: Plate Tectonics, both lessons are included in Practice Tests.

[divider]The following transcript is provided for your convenience.[divider]The moment magnitude scale which we can abbreviate “M” with a little “w”, is a scale that takes the total energy released into account. The Richter scale is thought of as outdated. Currently, the moment magnitude scale is what is usually looked towards large quakes and measured worldwide on the moment magnitude scale. That’s because the Richter scale is best used for local quakes, measuring five of less.

That leaves me to my next point. You may be thinking, “What does it mean for the earthquake to be measured five or less?” Basically, the Richter scale and the moment magnitude scale take the magnitude and they convert it into a number on a scale. Instead of saying, “How big is the earthquake?” and you answering, “It had a magnitude of this number” Instead you could say, “This was a magnitude two earthquake or a magnitude seven earthquake” It’s a really easy way to classify an earthquake. You get a general idea of how strong that earthquake was. The moment magnitude scale and the Richter scales coincide over the medium-range of earthquake intensities but diverge at small and large intensities.

For the middle range of earthquakes, they’re pretty much the same, but you begin to see the differences at small and large intensities. The reason for that is because they take the information from the seismometer and look at it differently. They focus on different points or parts of an earthquake.

It’s important to kind of get an idea of how big a unit is on one of these scales. An earthquake of magnitude six on the Richter scale is going to be one hundred times stronger than a magnitude four earthquake. We can break that down by saying an increase of two units equals a one hundred times increase in amplitude and a one thousand times increase in released energy. This is kind of, I guess a definition of how big a unit is on one of these scales.

This applies to the moment magnitude scale and the Richter scale. An increase of two units equals a one hundred times increase in amplitude and a one thousand times increase in released energy. There are some other seismograph-based Richter scales which includes the body wave and the surface wave magnitude scales such look at how earthquakes are measured.

The next lesson: Plate Tectonics, both lessons are included in Practice Tests.