Archive for March 11th, 2010

Science at home: More on the Chilean earthquake

(Editor’s note: there’s been a lot to talk around here regarding the recent earthquake in Chile. Here’s another take on the science of large-scale natural events.)

by Katie Bowell, Curator of Cultural Interpretation

Although none of us will have noticed a difference, scientists at NASA have calculated that the 8.8 magnitude earthquake that struck Chile on February 27 was so powerful that it may have shortened the length of a day and shifted the Earth’s axis.

The earthquake, the seventh largest in recorded history, shifted enough rock on our planet – around 400 kilometers of the Earth’s crust – to redistribute Earth’s mass and speed up its rotation. A faster rotation equals a shorter day. The resulting change is slight, as our days have hypothetically shortened by only 1.26 microseconds (1 microsecond =  one millionth of a second), but the change is permanent.

NASA also calculates that the earthquake moved the Earth’s figure axis by around eight centimetres (3 inches). The Earth’s figure axis is not the same as the north-south axis, but rather is the axis around which the Earth’s mass is balanced (the two axes are about 10 meters, or 33 feet, apart from each other).

If the earthquake in Chile, an 8.8 on the Richter scale, was strong enough to shorten days and shift the Earth’s axis, why didn’t the 7.1 magnitude earthquake in Haiti in January do something similar? Well, it helps to know a little about how the Richter scale works. The Richter scale measures earthquakes on a base-10 logarithmic scale, which means that each whole number you go up on the scale, the amplitude of the ground motion recorded on a seismograph goes up by a factor of 10.  So, while Chile’s 8.8 magnitude earthquake was only 1.7 steps above Haiti’s 7.1 magnitude earthquake on the Richter scale, it was almost 20 times stronger.

March 2010

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