A graphical device, an earthquake nomogram, can be used to estimate the magnitude of an ea...

A graphical device, an earthquake nomogram, can be used to estimate the magnitude of an earthquake if we know our distance from the epicenter and can determine the amplitude of the seismic wave measured on a seismogram.

In the diagram, the plotted line represents a simulated earthquake that had a 24-second interval between the arrival of the P and S waves. This represents a distance of about 210 kilometers from the recording station. The earthquake produced a recorded seismic wave with 23 millimeters of amplitude. Drawing a line between the 24-second point on the S-P scale and 23 millimeters on the amplitude scale allows the magnitude to be determined (5). Answer the questions that follow.

1. Two earthquakes occurred 100 kilometers away with recorded amplitudes of a) 10 millimeters; b) 100 millimeters. What were the magnitudes of these earthquakes?

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2. An earthquake of magnitude 6 has a recorded amplitude of 50 millimeters on the seismogram. How far away is the earthquake source, and what was the difference between the arrival times for S and P waves?