The Richter Scale (Click here to a MSWord version of this page.)

A scale for comparing the intensities of earthquakes was devised around 1940, by a man named Charles Richter. The intensity of an earthquake is measured by the amount of ground motion as measured on a seismometer. The Richter scale is not designed so that you must know the actual intensities or seismometer readings. The scale is simply used to compare intensities according to the following rule:

Each increase of 1 unit in magnitude on the Richter scale corresponds to a 10-fold increase in intensity as measured on a seismometer.

This makes it relatively easy to compare the intensities of earthquakes with a magnitude difference of integer amounts. For example, the 1976 Italy earthquake was a magnitude of 6.5, while the Guatemala earthquake of the same year had a magnitude of 7.5, which is exactly one unit greater. This means the second earthquake was 10 times more intense than the first.

How do we compare the intensities of earthquakes that do not differ by a whole number?

We can do this by using a property of exponents. If we express the intensity I as an exponential function of the magnitude M.

We will use the Alaska and Turkey earthquakes of 1964 and 1966.

	This represents the Alaska earthquake. And this is the Turkey earthquake.  We are asked to compare intensities, so the ratio will be useful. =39.81 =approximately 40 times as intense.
	3) Calculate the intensity difference between a 5.5 and a 6.2 magnitude earthquake. 4)  Calculate the intensity difference between an 8.5 and a 2.7 magnitude aftershock.

We can also use exponents to calculate the energy of an earthquake. The formula for the energy (in kWh, kiloWatt hours) is:
                                          where E is the energy, and M is the earthquake magnitude.

Now that you understand the Richter scale, let's try to discover what effect the large earthquake will have on Vancouver.