The earthquake
The earthquake that took place was a result of subductive plates. The Pacific plate was being subducted beneath the Okhotsk plate. (A subplate of the North-American plate) The Pacific plate moves at a speed of 9 cm per year, which is relatively fast for a tectonic plate. As a result of this subduction the island of Japan shifted approximately 8 feet in certain areas. (According to Dr. Daniel McNamara-seismologist for U.S. Geological Survey) The subduction of the Pacific plate also shifted part of the earth’s mass closer to the center of the earth, as one plate slid under the other. This changed the distribution of mass and therefore affects the inertia of the earth. As the mass moves towards the center the angular momentum increases and the earth turns a little bit faster. The earthquake in Japan caused the days to shorten by approximately 1.8 microseconds. This shortening shouldn’t have any noticeable effect as it is so minute. An average year usually varies by about 1000 microseconds due to other mass distributions. There have also been other earthquakes that have had the same effect of shortening the year. The 2010 earthquake in Chile (8.8) shortened the day by 1.26 microseconds. The 2004 earthquake in Sumatra (9.1) shortened the day by 6.8 microseconds.
Sources
Sources
http://www.cbsnews.com/stories/2011/03/13/scitech/main20042590.shtml
http://www.nasa.gov/topics/earth/features/japanquake/earth20110314.htm
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