# Earthquake Magnitude and Intensity

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• Created by: Jelena
• Created on: 15-05-13 15:37

## Ways to Measure the Size of an Earthquake

• 3 ways to measure the size of an earthquake
• 1. Richter Magnitude
• 2. Moment Magnitude
• 3. Modified Mercalli Intensity Scale
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## Richter Magnitude

• The amount of energy released during an earthquake is measured by its magnitude
• Charles Richter took the logarithm of the largest ground motion registered by a seismograph as his emasure of earthquake magnitude and came up with the Richter Magnitude Scale
• Two earthquakes at the same distance from a seismograph that dfifer in size of ground motion by a factor of 10 differ in magnitude by 1 Richter unit
• Ex. the ground motion of an earthquake of magnitude 3 is 10 times that of an earthquake of magnitude 2
• Ex. the ground motion of an earthquake of magnitude 6 is 100 times that of an earthquake of magnitude 4
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## Moment Magnitude

• Most seismologists today use the Moment Magnitude Scale
• A measurement more directly related to the physical properties of the faulting that causes the earthquake
• Proportional to the logarithm of the area of the fault break and is approximately proportioned to the logarithm of the seismic energy released during the rupture
• Both Richter's method and the Moment Magnitude method give roughly the same number
• The Moment Magnitude can be measured more accurately from the seismographs, and it can also be deduced directly from field measurements of faulting
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## Modified Mercalli Scale

• Measures the amount of damage done to the structures involved
• This measurement, called the intensity of an earthquake, is determined using the modified Mercalli scales
• This scale rates the types of damage and other effects of an earthquake as noted by observers during and after its occurrence
• Scale uses Roman numerals I to XII to designate degree of intensity; the higher the numeral, the worse the damage
• Specific effects or damage correspond to specific numerals
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