One simple calculation is the ratio of the total rotational energy of
the planet (which is simple to calculate) to the energy release of
the earthquake.
The magnitude of the earthquake probably has a relation to the total
energy release. This must put an upper limit on the change of time.
Since the mass of the planet is conserved, we have the moment of the
planet and its rotational energy as variables.
The radius of the planet may have changed, so we will eagerly wait to
see the rate of change of the rotation rate.
It is also possible that the earthquake only caused a phase shift in
the planets rotation, i.e. the rate of rotation stays the same but
the time of sunrise has shifted slightly.
Maybe that someone who knows about these things will tell us more.
cheers,
Neville Michie
On 16/03/2011, at 12:29 AM, jimlux wrote:
On 3/15/11 6:20 AM, jimlux wrote:
On 3/15/11 1:49 AM, Chris H wrote:
I hear in the Media that the earth quake sped the rotation of the
earth
up..
Can anyone confirm this?
No.. the magnitude of the change is parts in 1E11 or thereabouts.
Regular old tidal drag slowing is bigger, and that's what mostly
contributes to leap seconds.
Another, potentially easier to detect, effect is that the axis of
rotation of the earth might have shifted.
An interesting question is whether earthquakes always lead to a
speeding up... Off hand, I would think that the general tendency is
for the gravitational forces to make the earth more smooth, which
would probably mean that the moment of inertia decreases (speeding
up the rotation). (that is, mountains fill ocean trenches in the
long run).
On the other hand, rotational forces make the earth more oblate,
which increases the moment of inertia. I seem to recall that the
inital predictions of oblateness were made by assuming that there's
an equilibrium between gravitational forces pulling in and
rotational forces pulling out.
And this doesn't even get into the fact that the earth is somewhat
pear shaped: wider south of the equator than north. ( most
certainly not a banana shape as reported by Sir Bedivere, but what
would a medieval experimenter with swallows know anyway)
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