Using the Richter Scale to Measure Earthquakes

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  • 0:05 What Is the Richter Scale?
  • 0:49 Measuring Ground Shaking
  • 2:51 The Moment Magnitude Scale
  • 4:01 Lesson Summary
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Lesson Transcript
Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

In this video lesson, you will learn about earthquake magnitude and how it is measured. You will also learn how that relates to the amount of energy released during an earthquake, as well as how common different magnitude earthquakes are around the world.

What Is the Richter Scale?

An earthquake is just what it sounds like - the quaking of Earth. The ground shakes and moves due to rock breaking below the surface. This movement of ground is called seismic activity, and while we can't always tell when, where, or how strongly an earthquake will hit, we can measure its magnitude while it's happening.

In 1935, Charles Richter developed the local magnitude scale, a scale used to measure the magnitude of earthquakes. Now called the Richter scale, these measurements tell us how much the ground shook during a quake and how much energy was released. This information comes from seismographs, which collect data and directly measure the amount of ground shaking.

Measuring Ground Shaking

The Richter scale runs from 1 - 10 (1 being the least in magnitude and 10 being the greatest), but it is logarithmic. This means that for each 1 point in increase on the scale we get 10 times more ground shaking. Let's look at an example. Say we have a magnitude 1 earthquake on the Richter scale, which is the lowest magnitude earthquake. Compare that with a magnitude 2 earthquake, which is only one step higher (remember, the scale runs from 1 - 10), and you now have 10 times more ground shaking than with the magnitude 1 quake.

Take another step up the scale, so from magnitude 1 to magnitude 3, and this is 10 times more than that first step, so we now have 100 times more ground shaking with just two steps up the scale. That's a lot of seismic activity!

Now let's see how this relates to the total energy released during an earthquake. Through measurements of seismic activity, scientists know that the energy released by an earthquake, which is what causes all that shaking and moving in the first place, increases 32 times for each step up the Richter scale. Take our example from before where we have a magnitude 1 and a magnitude 2 quake. The magnitude 2 quake will have 32 times more energy than the magnitude 1 earthquake.

Now let's compare our magnitude 1 and magnitude 3 quakes. The magnitude 3 quake is two steps up the Richter scale, so we have 32 times more energy for the first step and then 32 times more energy than that up the second step. 32 times 32 gives us about 1,000 times the energy with just two steps up the scale! This is even more amazing when you compare this with the difference in ground shaking. A magnitude 3 earthquake has 100 times more ground shaking than a magnitude 1 quake but about 1,000 times the energy. That's a big difference!

The Moment Magnitude Scale

The Richter scale was originally designed to measure medium-sized earthquakes, those between magnitude 3 and 7, and within a distance of about 400 miles. The moment magnitude scale was created in 1979 to deal with these issues, but it builds on the Richter scale because it was already so accurate for small- to medium-sized quakes. The moment magnitude scale is the currently accepted scale used to measure medium- to large-sized earthquakes.

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