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Earthquake of March 28, 1964, Prince William Sound, Alaska. The magnitude 8.5 earthquake killed 131 people and caused 538 million in property damage. An area consisting of 120,700 km2 was shaken with damaging intensity.
Understanding Magnitude
Earthquakes are recorded by a seismographic network. Each seismic station in the network measures the movement of the ground at their site. When an earthquake occurs, it releases energy in the form of waves that radiate from the earthquake source in all directions. The different types of energy waves shake the ground in different ways and also travel through the earth at different velocities.
There are many ways to measure different aspects of an earthquake. Magnitude is the most common measure of an earthquake's size. It is a measure of the size of the earthquake source and is the same number no matter where you are or what the shaking feels like. The Richter scale measures the largest wiggle on the recording, but other magnitude scales measure different parts of the earthquake.
Earthquakes release a tremendous amount of energy, which is why they can be so destructive. The table below shows magnitudes with the approximate amount of TNT needed to release the same amount of energy.
