Ask A Scientist Environmental Earth Science Archive

name         Luanne
status       other
grade        other
location     CA

Question -   Hello - We are watching the News regarding the
devastating earthquake in Indonesia.  I just read that it may have
disturbed the earth's rotation.
"All the planet is vibrating" from the quake, said Enzo Boschi, the head
of Italy's National Geophysics Institute. Speaking on SKY TG24 TV, Boschi
said the quake even disturbed the Earth's rotation.
http://earthquake.usgs.gov/eqinthenews/2004/usslav/
What does that mean and what can that do?
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Web sites that relate to this topic:

United States Geological Survey:
http://www.usgs.gov/

http://earthquake.usgs.gov/eqinthenews/2004/usslav/


http://www.geophys.washington.edu/tsunami/intro.html

NEWTON BBS System Operators
=====================================================
The earth, although hard, is elastic. When some sort of high energy event
occurs (earthquake, volcano, explosion of a nuclear device) the earth can
"ring" -- a geological bell of sorts. Sensitive seismometers at numerous
locations around the world can detect these earth-vibrations. In fact, the
echoes of the vibrations can also be detected. There is no global danger
from such events (except maybe the atmospheric dust from a volcano), but
obviously from the news disaster can occur at a local level and even
hundreds of miles away.

Vince Calder
====================================================
       
NOTE: this posting is from an outside  source from NEWTON  BBS.

Quake rattled Earth orbit, changed map of Asia:  US geophysicist

An earthquake that unleashed deadly tidal waves on Asia was so powerful it 
made the Earth wobble on its axis and permanently altered the regional 
map, US geophysicists said.
The 9.0-magnitude temblor that struck 250 kilometers (155 miles) southeast 
of Sumatra island Sunday may have moved small islands as much as 20 meters 
(66 feet), according to one expert.
"That earthquake has changed the map," US Geological Survey expert Ken 
Hudnut told AFP.
"Based on seismic modeling, some of the smaller islands off the southwest 
coast of Sumatra may have moved to the southwest by about 20 meters. That 
is a lot of slip."
The northwestern tip of the Indonesian territory of Sumatra may also have 
shifted to the southwest by around 36 meters (120 feet), Hudnut said.
In addition, the energy released as the two sides of the undersea fault 
slipped against each other made the Earth wobble on its axis, Hudnut said.
"We can detect very slight motions of the Earth and I would expect that 
the Earth wobbled in its orbit when the earthquake occurred due the 
massive amount of energy exerted and the sudden shift in mass," Hudnut said.
Another USGS research geophysicist agreed that the Earth would have got a 
"little jog," and that the islands off Sumatra would have been moved by 
the quake.
However, Stuart Sipkin, of the USGS National Earthquake Information Center 
in Golden Colorado, said it was more likely that the islands off Sumatra 
had risen higher out of the sea than they had moved laterally.
"In in this case, the Indian plate dived below the Burma plate, causing 
uplift, so most of the motion to the islands would have been vertical, not 
horizontal."
The tsunamis unleashed by the fourth-biggest earthquake in a century have 
left at least 23,675 people dead in eight countries across Asia and as far 
as Somalia in East Africa.
The tsunamis wiped out entire coastal villages and pulled beach-goers out 
to sea.
The International Red Cross estimated that up to one million people have 
been displaced by the natural calamity.

Steve Miller
====================================================
The Sumatran earthquake will not alter the Earth's tilt (23½°), but
will probably alter the Earth's wobble on that axis. The Earth's north
pole gradually spirals around, anti-clockwise, on the Earth's surface
(in a diameter of about 2-12 metres); generally the tighter, the
faster the rotation.

However, if a tsunami (caused by an earthquake) starts in the middle
of an ocean, then the rotational effects of the westward tsunami would
likely to be cancelled out by the effects of the eastward tsunami. BUT
as the Sumatran earthquake was considerably nearer one shore than the
other, the rotational effects will be lop-sided. Even though each
tsunami had a horrific force, and did not actually form near the
epicentre, it is hard to say by how much. [Tsunamis only come into
being, or grow considerably bigger, when the sea gets shallow.]

Although the tsunamis had a force of hundreds of megatons of TNT, this
is somewhat small when it is up against the momentum of the Earth's
rotation, the Earth will not come to a screeching halt, but a leap second
in atomic time (UTC) might be necessary sooner than expected.

It will be interesting to see what the results from the International
Earth Rotation and Reference Systems Service
(IERS)(http://www.iers.org) published each Thursday.

Howard Barnes
====================================================
Thank you for your question, Luanne…  This event is simply tragic,
and the loss of life unimaginable.  In this age of preoccupation with
the threats of war and terrorism, it is easy (sadly) to forget that
nature can wield such destructive power, and wield it so
indifferently.  I am not so sure that any line of reasoning could
ever produce substantial justification for the death of 40,000+
people, but perhaps some solace will be found in whatever progress
might be made, as a consequence of this disaster, in safeguarding
lives from future earthquakes.

Because earthquakes involve movements of tectonic plates (and large
quantities of water, in the case of submarine earthquakes), they
necessarily involve relatively rapid movements of large amounts of
mass.  When this mass moves, the distribution of Earth’s mass
changes and results in slight deviations in the rotational motion
(e.g., angular velocity and axial tilt) of the planet.  To illustrate:
a figure skater pirouetting with his or her arms extended has a
specific way in which their body mass is distributed with respect to
their rotational axis (the rotational axis, incidentally, is an
imaginary line that extends through the middle of the rotating object
in a direction that is perpendicular to the direction of rotation…
think of a line connecting the North and South poles, for example).
If the figure skater then pulls one of their arms slightly closer to
their body, the way in which their body mass is distributed is
altered, thus causing their rotation to change.  The intensity of that
change is proportional to the degree to which the distribution of
their body mass is altered.  A spinning skater who bends but a single
finger toward their body may not feel a significant change in their
rotation; a spinning skater who pulls an arm in completely flush with
their body may produce so great a change in their rotation as to fall
down.

In the case of earthquakes, the amount of redistributed mass is
comparably small to the mass of the entire planet.  Likewise, the
distance over which that mass is moved is comparably small to the
size, or radius, of the planet.  Thus, the mass redistribution is
effectively small, in the grand scheme of things.  But, earthquakes
still do cause some minor change to Earth’s rotation; it is purely
an inescapable consequence of physics.  If a large (read: unfathomably
big) enough earthquake (or any seismic event, for that matter)
occurred, such that very extensive portions of Earth’s crust moved,
causing the planet’s rotation to become significantly altered, the
global climate could potentially be affected.  In the case of this
most recent seismic activity in Indonesia, however, Earth’s rotation
will not likely be altered to such a degree that it will have
significant, climatic consequences.
I hope this explanation helps.

Scott J. Badham
Department of Geology and Geophysics
University of Wyoming
=====================================================
    Below are preliminary values from the International Earth Rotation
and Reference Systems Service (IERS) for 2004 December 1st to 30th.
This period encompasses the 26th December 2004, the date of the
Sumatran tsunami.

    Even though there was a gain (of +0.000152) on the 26-27th, not all
of it is attributable to the tsunami as the daily gain, or negative
loss, was trending in that direction anyway.

HOWARD BARNES.
==============

    x = the Greenwich meridian (0°) and
    y = 90° West.
    UT1-UTC = difference between UT1 (mean time; ie. Earth rotation
time) and Coordinated Universal Time (UTC; ie. atomic time)

    Units used: Arcseconds for x and y.
                Seconds of time for UT1-UTC.

                                   ( Mean Time )
                                   (     v.    )
                 (  Polar Motion  )(Atomic Time)    UT1
       DATE           x       y       UT1-UTC       gain
    2004/12/01    .19738   .29342    -.488389        --
    2004/12/02    .19599   .29117    -.488527    -0.000138
    2004/12/03    .19396   .28871    -.488687    -0.000160
    2004/12/04    .19212   .28639    -.489137    -0.000450
    2004/12/05    .19046   .28436    -.489806    -0.000669
    2004/12/06    .18881   .28242    -.490669    -0.000863
    2004/12/07    .18738   .28036    -.491675    -0.001006
    2004/12/08    .18611   .27844    -.492754    -0.001079
    2004/12/09    .18436   .27687    -.493800    -0.001046
    2004/12/10    .18218   .27458    -.494698    -0.000898
    2004/12/11    .18028   .27249    -.495325    -0.000627
    2004/12/12    .17843   .27051    -.495677    -0.000352
    2004/12/13    .17655   .26851    -.495880    -0.000203
    2004/12/14    .17472   .26644    -.496098    -0.000218
    2004/12/15    .17315   .26424    -.496476    -0.000378
    2004/12/16    .17187   .26216    -.497079    -0.000603
    2004/12/17    .17030   .26040    -.497909    -0.000830
    2004/12/18    .16928   .25879    -.498905    -0.000996
    2004/12/19    .16859   .25729    -.499987    -0.001082
    2004/12/20    .16743   .25574    -.501015    -0.001028
    2004/12/21    .16590   .25400    -.501904    -0.000889
    2004/12/22    .16442   .25207    -.502584    -0.000680
    2004/12/23    .16297   .25011    -.503048    -0.000464
    2004/12/24    .16142   .24851    -.503328    -0.000280
    2004/12/25    .15984   .24722    -.503356    -0.000028
    2004/12/26    .15820   .24630    -.503242    +0.000114
    2004/12/27    .15635   .24532    -.503090    +0.000152
    2004/12/28    .15453   .24392    -.502939    +0.000151
    2004/12/29    .15281   .24236    -.502848    +0.000091
    2004/12/30    .15103   .24081    -.502926    -0.000078
=====================================================