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Aim: How are Earthquakes Measured?
Introduction: Some seismic events are stronger and do more damage than others. The most violent earthquake in modern times was probably a 1960 event centered in the Pacific Ocean off the coast of Chile. But this earthquake did not have the human toll of two earthquakes that occurred in China, one in 1556 and the other in During these earthquakes, buildings were destroyed and hundreds of thousands of people died.
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I. Earthquake Scales Seismologist use two different methods to measure earthquakes.
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A. Mercalli Scale Based on the reports of people who felt the earthquake and observed the damage it caused.
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Problems with Mercalli Scale
Based on the picture above, hypothesize the Mercalli rating for this earthquake.
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B. Richter Scale Based on measurements made with an instrument called a seismograph. It is more precise because it is based on measurement with a tool. It is a LOGARITHMIC scale- an increase in one unit translates to a 10-fold increase in the quantity measured.
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Seismograph
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Richter Scale Richter Magnitude TNT Energy Equivalent Example 1.0
6 ounces Construction site blast 1.5 2 pounds WWII Conventional bombs 2.0 13 pounds Late WWII Conventional bomb 2.5 63 pounds WWII Blockbuster bomb 3.0 397 pounds Massive Ordnance Air Blast Bomb 3.5 1,000 pounds Chernobyl Nuclear Disaster 1986 4.0 6 tons Small Atomic Bomb 4.5 32 tons Average Tornado 5.0 199 tons Nagasaki Atomic Bomb 5.5 500 tons Massena, NY 1994 6.0 6,270 tons Double Spring Flat, NV 1994 6.5 31,550 tons Coalinga, CA 1983 7.0 199,000 tons Hebgen Lake, MT 1959 7.5 1,000,000 tons Landers, CA 1992 8.0 6,270,000 tons San Francisco, CA 1906 8.5 31,550,000 tons Anchorage, AK 1964 9.0 199,999,000 tons 2004 Indian Ocean Earthquake
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THE END!
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