Chilean Quake May Have Shortened Earth Days

Chilean Quake May Have Shortened Earth Days

This view of Earth comes from NASA's Moderate Resolution Imaging Spectroradiometer aboard the Terra satellite.

March 01, 2010


The Feb. 27 magnitude 8.8 earthquake in Chile may have shortened the length of each Earth day.

JPL research scientist Richard Gross computed how Earth's rotation should have changed as a result of the Feb. 27 quake. Using a complex model, he and fellow scientists came up with a preliminary calculation that the quake should have shortened the length of an Earth day by about 1.26 microseconds (a microsecond is one millionth of a second).

Perhaps more impressive is how much the quake shifted Earth's axis. Gross calculates the quake should have moved Earth's figure axis (the axis about which Earth's mass is balanced) by 2.7 milliarcseconds (about 8 centimeters, or 3 inches). Earth's figure axis is not the same as its north-south axis; they are offset by about 10 meters (about 33 feet).

By comparison, Gross said the same model estimated the 2004 magnitude 9.1 Sumatran earthquake should have shortened the length of day by 6.8 microseconds and shifted Earth's axis by 2.32 milliarcseconds (about 7 centimeters, or 2.76 inches).

Gross said that even though the Chilean earthquake is much smaller than the Sumatran quake, it is predicted to have changed the position of the figure axis by a bit more for two reasons. First, unlike the 2004 Sumatran earthquake, which was located near the equator, the 2010 Chilean earthquake was located in Earth's mid-latitudes, which makes it more effective in shifting Earth's figure axis. Second, the fault responsible for the 2010 Chiliean earthquake dips into Earth at a slightly steeper angle than does the fault responsible for the 2004 Sumatran earthquake. This makes the Chile fault more effective in moving Earth's mass vertically and hence more effective in shifting Earth's figure axis.

Gross said the Chile predictions will likely change as data on the quake are further refined.


(Source: http://www.jpl.nasa.gov/news/news.cfm?release=2010-071&rn=news.xml&rst=2504)


Ofcourse any change measured in microseconds isn't noticeable a day, but I guess most people don't even know what the figure axis is.

I find it amazing that a regional even can move the whole planet.

Reminds me of the fact I saw on How the Earth Made Us:

The large number of reservoirs we've built in the northern hemisphere has shortened the day by a few millionths of a second.

Truronian said:

The large number of reservoirs we've built in the northern hemisphere has shortened the day by a few millionths of a second.

Click to expand...

Lolwut?

Guys, you affect the rotation of the planet each time you fart. By a very tiny amount, but you do.

I imagine the direction of the movement at the fault is relevant - the Chilean quake was east-west with the subducting ocean plate "snapping" in the direction of the Earth's spin. The 2004 quake was along a subduction zone in a NE - SW direction.

Should have been important to note in the OP that the day is getting longer naturally due to loss of angular momentum to the moon.

Do elaborate.

PlutonianEmpire said:

Lolwut?

Click to expand...

More reservoirs near the north pole => water on average slightly nearer the earth's axis of rotation => faster rotation to conserve angular momentum.

warpus said:

Guys, you affect the rotation of the planet each time you fart. By a very tiny amount, but you do.

Click to expand...

Vertical farting avoids such problems.

What if everyone in the US went to the California coast and jumped up and down in unison... would that make a tidal wave a 100 feet tall take out China? Or would it make Cali. sink into the ocean?

^ maybe both!

Truronian said:

More reservoirs near the north pole => water on average slightly nearer the earth's axis of rotation => faster rotation to conserve angular momentum.

Click to expand...

Makes sense now.

Yeah, the effect is insignificant compared to what the moon is doing. Eventually we will be tidally locked with the moon (so the moon will only be visible from one hemisphere). We can only see one side of the moon, and that's what the moon is going to do to us eventually.

I thought axis shifts were how the Sahara desert was started. So this might be a chilling thought, huh?

So just in a doomsday mentality, is there some sort of mean seismic trend for the world that might be accelerating?

Technically speaking it is possible that days were shortened as a result from the earthquake in Chile. But in fact as noted in the article, the 2004 Indian Ocean earthquake had the same effect.

It has to be noted that axial tilt (more known as earth's inclination) varies between 22.1° and 24.5° (but see below), with a 42,000 year period.

JEELEN said:

Do elaborate.

Click to expand...

Tidal acceleration. The gravitational torque between the Moon and the tidal bulge of the Earth causes the Moon to be promoted in its orbit, and the Earth to be decelerated in its rotation. Effectively, energy and angular momentum are transferred from the rotation of the Earth to the orbital motion of the Moon, although most of the energy lost by the Earth is converted to heat, and only about 1/30th is transferred to the Moon. 620 million years ago, the day length was ~22 hours long.

Note that this was computed out of a MODEL and not actually measured. It cannot be measured because the signal to noise ratio is way to poor. We don't know how accurate this model is and besides, every year the day increases with 15 microseconds. (due to the moon as stated above)