Using a complex model to perform a theoretical calculation based on a U.S. Geological Survey, Richard Gross of NASA's Jet Propulsion Laboratory (JPL) has determined that by changing the distribution of the Earth's mass, the earthquake that devastated Japan last Friday should have sped up the Earth's rotation, resulting in a day that is about 1.8 microseconds (1.8 millionths of a second) shorter.
The calculations, which will likely change as the data on the Japan quake is further refined, have also been used to examine the effects of other recent quakes. Gross estimated that last year's 8.8 earthquake in Chile shortened the length of a day by about 1.26 microseconds, while similar calculations revealed the 9.1 magnitude Sumatran quake of 2004 shortened the day by 6.8 microseconds. Just how much an earthquake affects the Earth's rotation depends on the magnitude of the quake, its locations and details of how the fault slipped.
Gross's calculations also indicate the Japan quake should have shifted the position of the Earth's figure axis by about 17 cm (6.69 in), towards 133 degrees east longitude. Not to be confused with the Earth's north-south axis, the figure axis is that about which the Earth's mass is balanced. While the slight shift will cause the Earth to wobble a bit differently as it rotates, it won't cause a shift of Earth's axis in space, which can only be affected by external forces such as the gravitational pull of the sun, moon or planets.
Gross points out that the changes to the Earth's rotation and shift of its axis aren't anything to be worried about. "Earth's rotation changes all the time as a result of not only earthquakes, but also the much larger effects of changes in atmospheric winds and oceanic currents," he said. "Over the course of a year, the length of the day increases and decreases by about a millisecond, or about 550 times larger than the change caused by the Japanese earthquake. The position of Earth's figure axis also changes all the time, by about one meter (3.3 feet) over the course of a year, or about six times more than the change that should have been caused by the Japan quake."
Although scientists are able to measure the larger effects of the atmosphere and ocean on the Earth's rotation, the changes due to earthquakes have been too small to measure as the computed change in the length of a day caused by earthquakes is much smaller than the accuracy with which scientists can currently measure changes in the length of a day.
However, the effects from the 9.0 magnitude Japan quake, which is the fifth largest since 1900, may actually be large enough for scientists to observe. This is because the position of the figure axis can be measured to an accuracy of about five cm (two inches), so the 17 cm shift from the Japan quake may be observable if the scientists can adequately remove the larger effects of the atmosphere and ocean from the equation.
The land doesn\'t just fall in one area without affecting the other sides, especially when it is up to 30 miles deep. It doesn\'t necessarily react immediately because 30 miles of land is a lot of resistance & the buckling takes time to occur. Eventually the stresses created will give way & we are talking about a 25 to 30 mile deep raft that is pushing up against another raft of similar depth. Understand that they all edge onto the Pacific plate except Peru where the Pacific plate runs directly into the Nazca plate, the fractures that have occurred in Japan, following Christchurch, encompassing the ongoing Solomon Islands\' quakes which occurred either side of the Indonesian quakes & following the major Ecuador/Peruvian quake. Realise that the Solomon Islands are kind of in the middle of the plate, well close & so it teeters around that space & so their quakes may rarely become massive, rather they get the shift in several directions consequently getting more of them but the places on the longer edges, like Peru, Japan, Indonesia, New Zealand & North America are destined to be hit hard.
I don\'t want to be wrong but I also would rather not be right. The problem here is that the signs are that the USA will be hit by the build-up of all these large earthquakes & being the last to release the stresses, may mean that the largest is yet to come because the stresses are being pushed back now from every other direction.
So, with that magnanimus statement. he admits that his efforts are a complete waste of time, and no doubt someone\'s money. I am totally amazed at the number of these so called scientific studies that have little or no effect on our daily lives, and yet someone is paying big money to these people to do it. Don\'t you wonder where the money comes from ?