Chilean Earthquake May Have Shortened the Length of a Day on Earth

[Yazman]

Source: http://www.universetoday.com/2010/03/01/chilean-earthquake-may-have-shortened-the-length-of-a-day-on-earth/

Snippet from source (click link for full article):


Yikes! Just how big was the magnitude 8.8 earthquake (http://www.universetoday.com/guide-to-space/earth/earthquake/) in Chile? One scientist says the shaking may have affected the entire planet (http://www.universetoday.com/guide-to-space/the-solar-system/planet/) by shifting Earth (http://www.universetoday.com/guide-to-space/earth/) on its axis. This possibly may have shortened the length of each day on Earth (http://www.universetoday.com/guide-to-space/earth/how-long-is-a-day-on-earth/) by about 1.26 microseconds. Using a complex model JPL research scientist Richard Gross computed how Earth's rotation (http://www.universetoday.com/guide-to-space/earth/earths-rotation/) should have changed as a result of the Feb. 27, 2010 quake. If his figures are correct, the quake should have moved Earth's figure axis (the axis about which Earth's mass (http://www.universetoday.com/guide-to-space/earth/earths-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 (http://www.universetoday.com/guide-to-space/earth/earths-axis/) by 2.32 milliarcseconds (about 7 centimeters, or 2.76 inches).


This isn't actually of political interest, I just figured you guys here at S&E would be interested. This sort of stuff is interesting to me so I figured somebody else here might appreciate it.

[Across The Street]

I also had heard that they recently downgraded the scale by 1 for magnitudes of quakes, which would make the Chilean quake a 9.8 but im not 100% on whther this is true or not. But the numbers in the article would make more sense.

[Belisarius]

i'm gonna ask it to my geography teacher this week (he's really good at this stuff). very interesting.

[piet11111]

i wonder what the cumulative effect has been over thousands of years of quakes.

[Dean]

Wat thats so weird. Thanks for the post!

[Belisarius]

i counted there are around 200 earthquakes per century. this means every century should be 200 microseconds shorter if one earthquake equals one microsecond (this one was 1.26, but we have to remember that there can also be earthquakes that lengthen a day and that not all earthquake are as strong and as far south or north as this one). it takes one million earthquakes to shorthen a day by one second. that equals 5,000 centuries or 500,000 years. the cumulative effect is thus next to nothing.

[piet11111]

i counted there are around 200 earthquakes per century. this means every century should be 200 microseconds shorter if one earthquake equals one microsecond (this one was 1.26, but we have to remember that there can also be earthquakes that lengthen a day and that not all earthquake are as strong and as far south or north as this one). it takes one million earthquakes to shorthen a day by one second. that equals 5,000 centuries or 500,000 years. the cumulative effect is thus next to nothing.

but there are way more earthquakes then 200 per century (seriously 2 a year ?)

i would not be surprised if there where more then 20 a day around the world.

fact check http://earthquake.usgs.gov/earthquakes/eqarchives/year/eqstats.php

2-2.9 = ~1,3 million a year
3-3.9= ~130.000 a year
4-4,9= ~13.000 a year
5-5,9= 1319 a year
6-6,9= 134
7-7,9= 17 a year
8 and more = 1 a year

the cumulative effect of all those quakes over thousands of years would add up.

[Belisarius]

but there are way more earthquakes then 200 per century (seriously 2 a year ?)

i would not be surprised if there where more then 20 a day around the world.

fact check http://earthquake.usgs.gov/earthquakes/eqarchives/year/eqstats.php

2-2.9 = ~1,3 million a year
3-3.9= ~130.000 a year
4-4,9= ~13.000 a year
5-5,9= 1319 a year
6-6,9= 134
7-7,9= 17 a year
8 and more = 1 a year

the cumulative effect of all those quakes over thousands of years would add up.
i checked the wikipedia list of the 20th century, but you have to take into account that only very strong ones really change anything and also that only the ones on the extreme south or north make a big difference, the ones on the equator don't change anything.

[Revy]

I remember them saying that about the earthquake that caused that tsunami in 2004.

[Klaatu]

Don't forget that many earthquakes move laterally (parallel to the surface) and would have no effect on the rotation. Vertically-moving earthquakes do have the effect of changing the planet's spin (by conservation of angular momentum) by speeding up (land mass moves inward) or slowing down (as land mass moves outward). Also keep in mind that any upheavals will in time erode back, thus slowly changing the whole rotation back to where it started from.

One other thing to consider is that as the polar ice caps melt away, and the oceans deepen, the earth's rotation will slow also, due to the greater mass of liquid water present at the equator. As the water mass bulges outward, earth's rotation slows, and the day becomes longer.

[MarxSchmarx]

The reason it's a little strange is that it's actually the core of the earth that is defining the unit of days viz. the sun. The crust itself runs on its own schedule, and is occasionally out of synch with the core. So this earth quake just adjusted the rotation time of the crust viz. it's relation to the core, which is why the day is shorter. An interesting tidbit tbs.