| BACK NEXT GEOLOGY INDEX STUDY QUESTIONS Earthquake Measurement Earthquake measurement is not a simple problem. It is hampered by many things. Few people are capable of observing carefully what is happening around them when they are experiencing an earthquake. Moreover, equipment and structures often fail during severe earthquakes. Also, most quakes only last seconds or at most, minutes. Lastly, effects of the same event vary widely from location to location. Therefore it is difficult to coherently and accurately describe what happens during an earthquake based on eyewitness accounts. To measure earthquakes we use two different scales. One measures the energy of the waves, the other the resulting amount of damage The Richter Scale The first, the Richter scale , is an absolute scale that measures the amount of ground movement and the energy released by an earthquake, its magnitude . An earthquake of magnitude 1 releases approximately as much energy as that generated by the explosion of one pound of TNT. Each number on the Richter scale represents a ten-fold increase in ground motion and an associated energy release of approximately 30 times that of the previous number. This means that an earthquake of magnitude 7 will be nearly 1,000 times more powerful than a magnitude 5 event. Earthquakes of magnitude 6 or greater are considered severe, and represent potentially devastating events. Unfortunately, they are not all that rare. Although the Richter scale gives a fairly accurate measurement of the amount of energy released, it does not give any information as to what happens to people and structures. For that, we use the Mercalli scale. | |
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