
Japan earthquake shortened days on Earth - _grrr
http://www.mb.com.ph/articles/309317/japan-earthquake-shortened-days-earth
======
nickolai
> The Earth's figure axis is not the same as its north-south axis in space,
> which it spins around once every day at a speed of about 1,000 mph (1,604
> kph). The figure axis is the axis around which the Earth's mass is balanced
> and the north-south axis by about 33 feet (10 meters).

Could someone explain this paragraph? how does one measure a rotation speed in
terms of distance over time ? And I just cant figure what the second sentence
means at all...

~~~
softbuilder
I think they're trying to describe <http://en.wikipedia.org/wiki/Precession>

------
ars
I wonder if we will finally get to use negative leap seconds.

~~~
benjoffe
I don't think this will directly lead to that happening. Assuming 1.8µs/day,
then it will take about 1/(365.25*1.8e-6) ≈ 1500 years for a 1 second
difference to accumulate. I believe the effects of terrestrial bodies have a
much larger effect.

------
EgeBamyasi
Oh boy!

That means the monthly pay only is only 11 days- 19.8microseconds away.

~~~
sophacles
And we will all live longer (in terms of days anyway)! Who needs a fountain of
youth? Just invent and earthquake ray. :)

------
Vivtek
This explains why I feel so tired this morning.

------
trebor
This is nothing more than an educated guess. While Gross is theoretically
correct, I'm not certain our implements can detect a 5.4 µSec change over 3
days. Not only that, I doubt it matters enough for us to care.

Assume that our sensors _are_ sensitive enough to detect this for a moment.
The day-length of the earth changed by:

    
    
        0.0000000000208333350570911 %
    

Who bloody well cares about that? I think scientific navel gazing just got a
new mascot.

~~~
sophacles
Woah...

1) our instruments can detect that much time change, no problem. NIST
standards measure time of day accurate to the nanosecond, an error of
thousands of those is noticeable.

2) Cumulative effects of this add up to close to a millisecond per year. That
is certainly noticeable to various applications.

3) Cries of "scientific navel gazing" almost always come from those who feel
slighted because they don't get it. This anger of course is misplaced, not
getting it is a strict result of not bothering to learn enough -- it has
nothing to do with anyone but the accuser.

~~~
trebor
Point 3 is nothing more than character assassination, and I'm disappointed
that you are voted up with that in your comment. I _do_ get it.

Point 2 is moot. Yes, the cumulative effect is felt—but I'm pretty sure we can
adjust for that. In fact, I'm certain that the applications which would notice
the change are adjusted for accuracy every so often.

Point 1 I concede; I just wasn't certain because I do not know the exact
methods by which we measure day length and the level of accuracy they have. I
am not blindly assuming that the day is exactly 86400 or 86400.25 solar
seconds.

\---

I do not consider the OP news-worthy. Aside from the attentions of these
incredibly accurate applications, which likely get their data from their own
mathematicians or from scientific journals, why should the rest of us care?

Perhaps I was wrong: this is story dredging, not scientific navel gazing. No
mainstream journal would care about this, except to raise its search rankings
by covering ANYTHING related to the Japan quake.

~~~
mturmon
You have a point about the story dredging in the OP. Here's a more carefully
sourced story that has more context:

[http://www.nytimes.com/2011/03/14/world/asia/14seismic.html?...](http://www.nytimes.com/2011/03/14/world/asia/14seismic.html?_r=1)

I think the overall displacement (around 13 feet as quoted in the article
above) is of interest to both specialists and to the lay public. Just as an
indicator of size.

The main thing that's of interest to earthquake people is not so much the peak
displacement, as the underlying stress/strain field (i.e., the forces and
displacements as a function of space). There will most certainly be a slew of
journal publications, as well as press releases, once the displacement data
are analyzed.

Here's an example of the latter, for the Landers earthquake, which was a M7.2
in 1992 in the desert east of LA:

[http://www.youtube.com/watch?v=giJaGdfavfs&feature=chann...](http://www.youtube.com/watch?v=giJaGdfavfs&feature=channel_video_title)

The closing frames show how the strain probably accumulated in the centuries
prior to the earthquake.

 __*

It may be helpful to say: what they're driving at with all this hyper-precise
GPS and displacement modeling is a forecast capability for earthquakes, same
as is done for weather. In both cases you have sparse measurements of fields
that are assimilated into a forward model.

