Humans have an innate drive to describe things. Man is a creature of measurement. Science is the answer to man’s drive to measure. Size and quantity are inherent to scientific measurement. Numbers make up data. For example, hurricanes are measured by category (1-5) based on wind speed. Tornadoes are measured on the Fujita scale (F1-F5) estimated by damage that is caused. Earthquakes are measured by magnitude (1-10) based on the energy released.
Earthquakes occur when tectonic plates slip. This shift causes the earth to shake. Earthquakes have been reported all through recorded time. In the 1930s, Charles Richter developed a means of comparing California earthquakes on a scale of 1 to 10. Using seismographs and the known epicenter (origin of earthquake), he was able to mathematically form a logarithm that described the earth’s movement.
Richter designed his measurement scale to compare California. The fault in this system is the distance between the location of the measuring seismograph and the earthquake’s epicenter. The Richter scale becomes unreliable when the distance exceeds 350 miles. The scale has proved to be excellent with low level earthquakes below 3.0 and adequate for middle level quakes 3.0-7.0. Upper level magnitudes are less precise.
Science’s need for more absolute values led a team of Harvard University scientists to develop the moment magnitude scale (MMS). Rather than being based on a comparison scale, it measures earthquakes in terms of energy released. Improved technology allows scientists to relate the earth’s rigidity to the amount of slippage within the area that the slippage occurs. As with the Richter scale, the measurement is expressed in logarithms. Using a log scale of 1 to 10, it means that the strength of an earthquake increases ten fold for each step. For example, the San Francisco earthquake measured magnitude 7.9 (MMS). The 2004 Indian Ocean earthquake registered a magnitude 9.3. The Indian Ocean quake released 14 times the amount of energy than did the San Francisco quake.
Earthquake measurement, like measurements for other disasters, are not totally accurate measurements of the effects of a disaster. Other factors not included in the reporting number are the concentration of people, kinds of buildings, soil type and substrate structure. These will have an impact on the disaster levels of an earthquake. The common citizen measures an earthquake on its death toll and property damage. The 1812 New Madrid earthquake measured a magnitude around 8.0. So few lives were lost that there was no record made of the dead. The Shaanxi, China of 1556 was estimated to the same magnitude but cost nearly a million lives.
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The moment magnitude scale has been adopted by the United States Geologic Survey as its official tool for measuring earthquakes. As a result the Richter scale has been more or less been replaced by the moment magnitude scale. Most earthquakes between 3.0 and 7.0 measure the same on either scale. The scale provide a means to describe how strong an earthquake is but It does measure the how disastrous an earthquake can be.
