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Potential to Kinetic

Earthquakes:

Exploring Earthquakes and the Modified Mercalli Scale

We can measure an earthquake by:

  • the amount of movement or energy released

  • its intensity or its effect of intensity

Magnitude

The magnitude (“size”) of an earthquake is based on the measurement of the maximum motion recorded by a seismograph.

courtesy of the US Geological Survey

Several scales of measurement have been developed.

  • The most familiar of these is the Richter scale - related to the size of seismic waves produced during a quake.

  • However, today seismologists more commonly rely on what is called the Moment Magnitude Scale, which measures the amount of energy released during an earthquake.

Intensity

The effect of an earthquake on the Earth's surface is referred to as its intensity.

Numerous intensity scales have been developed over the last several hundred years. The one currently used in the United States is the Modified Mercalli Intensity Scale developed in 1931.

Here is a photograph of Giuseppe Mercalli, the inventor of the Mercalli Scale (From Walker, 1982).

courtesy of the US Geological Survey

Modified Mercalli Intensity Scale

This is a semi-quantitative scale used to evaluate ground shaking and damage.

This scale is composed of 12 increasing levels of intensity based on observed effects. These range from imperceptible shaking to catastrophic destruction, designated by Roman numerals.

It is influenced by the amount of kinetic energy released, the substrate, the buildings, etc. Although it confounds many variables, it is valuable in

  • evaluating ground shaking in modern quakes

  • evaluating historic earthquakes, where written records exist.

This postcard shows the damage effect of different earthquakes in Los Angeles.

Resources:

Modified Mercalli Intensity Scale - A copy of the scale composed of 12 increasing levels of intensity based on observed effects. http://neic.usgs.gov/neis/general/handouts/mercalli.html

Did You Feel It? This is a web site through which you can report your own experiences during an earthquake, so that the USGA can use the Mercalli Scale of Intensity to map out ground shaking. For further information visit http://pasadena.wr.usgs.gov/shake/

Tremor Troop Earthquakes, Federal Emergency Management Agency, FEMA 159, April 1999, published by the National Science Teachers Association. Single copies of this publication may be obtained from FEMA at no cost by calling 1-800-480-2520.

This is a complete binder of activities for Grades K-6. A fun and creative classroom activity to illustrate earthquake intensity can be found on pg. 110 – The Mercalli Scale – Calling Station KWAT.

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