[Geysers] Chilean Earthquake

[Michael Goldberg]

I am not a geologist, but here goes:

Whenever the earth shakes in one place, the motion ripples outward in all 
directions until it is all absorbed by things like friction and/or 
gets spread so thin that nobody can tell it's there.  Similar things 
happen on a small scale if you pick up the corner of a blanket and shake 
it.

Solid rock transmits the motion with surprising efficiency because it is 
so rigid -- if you shake one corner of a large stone, the whole thing 
gets dragged along for the ride.  So when one piece of the Earth suddenly 
shifts by 5 feet or more, the resulting ripples are strong enough to 
travel around and through the entire planet.  At Old Faithful the ripples 
are too small to feel but a seismograph can tell they're there.

It is easier to see what happened yesterday (Feb. 26) afternoon when there 
was a magnitude 7.0 earthquake near Okinawa.  The first waves reach 
Yellowstone at 1:29pm.  Then they keep circling the Earth and come back at 
2:13pm and once or twice more before dying out.

Last night's magnitude 8.8 Chilean earthquake was so big that some places 
along the fault line probably moved 50 feet or more.  It released so much 
energy that the Earth kept ringing like a gong for a couple of hours 
afterward, long after the main pulse died down.  You can see it in the 
slow rhythmic oscillations in the seismogram that keep going until almost 
3:00am.

The colors are just a timekeeping device.
The black goes from the top of the hour until :15 past.
The red line goes from :15 past the hour to :30 past. 
The blue line goes from :30 past the hour to :45 past.
The green line goes from :45 past the hour to the top of the next hour.

It helps us keep track of things when there's a big earthquake and the 
lines get all jumbled up on top of each other.

By the way, pretty much everything we know about the inside of the earth 
comes from watching how earthquake waves travel through it.  The patterns 
of refraction and distortion give clues to the different layers deep 
underground.  The fact that certain types of waves get bogged down near 
the center of the Earth is our clue that one of the layers is molten rock
rather than solid.  And there is still a lot that we don't know yet.

Michael Goldberg
michael.goldberg at uc.edu

On Sat, 27 Feb 2010, SkibumBill at aol.com wrote:

> Why does it show up on Seismographs on another continent?  What do the 
> colors mean?
>
> In a message dated 2/27/2010 10:25:11 A.M. Central Standard Time, dmonteit at comcast.net writes:
> The Chilean earthquake is clearly visible on the seismographs in
> Yellowstone.  The earthquake was at 2334 local and was noted at Old
> Faithful at 2342.  All seismograph (Webicorder displays) throughout the
> inermountain west look about the same.
>
> <http://quake.utah.edu/helicorder/yft_webi.htm>
> <http://news.bbc.co.uk/2/hi/americas/8540289.stm>
>
> Dave