21世紀最も地震が頻繁に起きた国はどこ？
Japan has had a long history of earthquake catastrophe and seismic activity. Earthquakes are the vibrations caused by rocks breaking under stress. The underground surface along which the rock breaks and moves is called a fault plane. Over time, stresses build beneath the earth’s surface. Occasionally, stress is released resulting in the sudden, and sometime disastrous shaking we call an earthquake. Earthquakes can cause shaking that could last seconds or minutes. Besides that, there may be several earthquakes over a period ranging from hours to weeks called aftershocks, and the magnitude of the following tremors will decrease with time. It is important to know the earthquake magnitude because it can be the clue if there will be any aftershocks. Because of that, magnitude can be measured on the Richter scale, invented by Charles F. Richter in 1934. The Richter magnitude is calculated from the amplitude of the largest seismic wave recorded for the earthquake. In the past twenty years, the most severe earthquake that occurred was in 2011 off the coast of Tohoku.
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