![]() The Earth's crust is stressed by tectonic forces. The irregular distribution of shaking arises from variations of geology and/or ground conditions. Considering that the energy release of a magnitude 2 quake is equal to about 50 kg of explosive while a magnitude 5 releases energy equivalent to 1,800,000 kg, we should be very thankful that they are so infrequent!ĭocument.Isoseismal map for the 1968 Illinois earthquake. Magnitude 10 earthquakes are extremely rare, occurring less than once a year. ![]() About 1,000,000 magnitude 2 earthquakes occur each year, compared with only about 1,000 magnitude 5 quakes. The Richter scale remains the standard for quakes smaller than 3.5 in magnitude, and luckily, this is where most earthquakes fall on the scale. The moment magnitude scale is the currently accepted scale used to measure medium- to large-sized earthquakes. ![]() 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 Richter scale was originally designed to measure medium-sized earthquakes, those between magnitude 3 and 7, and within a distance of about 400 miles. A magnitude 3 earthquake has 100 times more ground shaking than a magnitude 1 quake but about 1,000 times the energy. 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. 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. Now let's compare our magnitude 1 and magnitude 3 quakes. The magnitude 2 quake will have 32 times more energy than the magnitude 1 earthquake. Take our example from before where we have a magnitude 1 and a magnitude 2 quake. 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. Now let's see how this relates to the total energy released during an earthquake. 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. This information comes from seismographs, which collect data and directly measure the amount of ground shaking. Now called the Richter scale, these measurements tell us how much the ground shook during a quake and how much energy was released. In 1935, Charles Richter developed the local magnitude scale, a scale used to measure the magnitude of earthquakes. 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. The ground shakes and moves due to rock breaking below the surface. What Is the Richter Scale?Īn earthquake is just what it sounds like - the quaking of Earth. ![]() As measured with a seismometer, an earthquake that registers 5.0 on the Richter scale has a shaking amplitude 10 times that of an earthquake that registered 4.0, and thus corresponds to a release of energy 31.6 times that released by the lesser earthquake. ![]() The Richter scale is a base-10 logarithmic scale, which defines magnitude as the logarithm of the ratio of the amplitude of the seismic waves to an arbitrary, minor amplitude. The Richter magnitude scale (also Richter scale) assigns a magnitude number to quantify the energy released by an earthquake. ![]()
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