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Magnitude

# Magnitude - GEOL 114 The Earth's Dynamic Interior Lecture...

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GEOL 114 The Earth's Dynamic Interior Lecture Notes (Copyright © 2006 by Jeffrey S. Barker) Lab 6. Earthquake Magnitude Question: What is the magnitude of an earthquake? How is it determined from measurements on a seismogram? How do estimates from a number of seismograph stations compare? Data: You will be given a plot of the vertical-component seismogram for a particular earthquake recorded at one station. Other students will be given seismograms from the same earthquake, but recorded at different stations. The station name and distance is printed at the top. Below this is the recorded seismogram; time windows including the P wave and surface wave are shaded. The P-wave portion is plotted below this, and the surface wave portion is plotted below that. The instrument response is plotted at the bottom. In this activity, you will calculate m b and M S from actual seismograms. m b is measured from the largest amplitude within about 10-15 seconds after the arrival of the P wave. M S is measured where the surface wave has a period of about 20 seconds, which may not be the largest portion of the surface wave. For both m b and M S , both amplitude and period must be measured and used to calculate magnitude. Amplitude is measured as the height from zero to the largest value (either positive or negative). If the signal is symmetric (similar size in positive and

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Magnitude - GEOL 114 The Earth's Dynamic Interior Lecture...

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