irisedu Education and Outreach Series No How Often Do Earthquakes Occur This figu was oduced in coop eration with the US Geological Surve and the University of Memphis Earthquakes are always happening somewhere 10 15 476 15000 476000 15000000 476000 ID: 11256
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1200NewYorkAve,#800WashingtonDC20005phone(202)682-2220fax(202)682-2444ww.iris.edu Education andOutreachSeries No.3HowOftenDoEarthquakesOccur?Thisfiguewas poducedincoop-erationwiththeUS Geological Surve, andtheUniversity of MemphisEarthquakes are always happening somewhere. 26481093751547615,000476,00015,000,000476,000,00015,000,000,000476,000,000,00015,000,000,000,000Number of Earthquakes per year (worldwide) 1,000,000100,00010,0001,500120181Energy Release(equivalent kilograms of TNT)Magnitudelargest recorded eathquakesdestruction over vast areamassive loss of lifegreat earthquakesevere economic impactlarge loss of lifemajor earthquakedamage ($ billions)loss of lifestrong earthquakeproperty damagemoderate earthquakeoperty damagelight earthquakeminor earthquakeoften feltgenerally not feltChile (1960)Alaska (1964)Sumatra (2004)Japan (2011)Chile (2010)San Francisco, CA (1906)New Madrid, MO (1812)Long Island, NY (1884)Large Lightning BoltAverage TornadoHiroshima Atomic BombMount St. Helens EruptionCharleston, SC (1886)Oklahoma City BombingModerate Lightning BoltKrakatoa EruptionWos Largest Nuclear Test (USSR) shaded tower. The shaded area indicates how many earthquakes of each unprecedented devastation due to poor building material and construction techniques resulting in estimates of $11 billion to reconstruct. The earthquake released the energy equivalent to 476 million kilograms of explosive, about 100 times the amount of energy that was released by the atomic bomb that destroyed the city of Hiroshima during World War II.Japan in 2011 also caused large tsunamis. All three were mega-thrust earthquakes on subduction-zone boundaries that, in a period of minutes, released centuries of accumulated strain and caused rebound in the overlying plates. Because great earthquakes release so much energy, the five largest earthquakes are responsible for half of the total energy released by all earthquakes in the last century.There has definitely been an increase in the number of earthquakes that can be due to a more-than 10-fold increase in the number of seismic stations world wide over the past century. This doesn’t mean that the annual average number of earthquakes has increased. In fact, earthquakes of