## Tuesday, March 02, 2010

### NASA: earthquake distorted Earth's motion

There used to be times when the motion of the celestial bodies was considered to be the ultimate symbol of accuracy and regularity. However, it was found out that the orbits were not proper circles but ellipses (or more complicated things, as determined by GR). Moreover, their parameters kept on changing according to some laws.

And today, we can even calculate and measure how they're failing to be regular because of special events such as the recent earthquake in Chile. NASA has made some calculations what it did with the Earth's balance and spin:
Chilean Quake May Have Shortened Earth Days
The earthquake has shortened the day by 1.26 microseconds or so. That's because the angular frequency has increased; it has increased because the moment of inertia has dropped; it has dropped because the Earth became more uniform and compact. Pieces of the Earth have fell into the holes.

Note that the change equals 1.5 x 10^{-11} of a day: another leap second just because of the Chilean earthquake would be needed after 10^{11} seconds or 3,000+ years. This relative accuracy, 10^{-11}, should be trivial to measure with the state-of-the-art atomic clocks that can achieve the relative accuracy up to 10^{-16} or something like that.

Also, the Earth's figure axis - around which the planet is "balanced", whatever it exactly means - has been separated from the axis of the spin by 10 meters or so. The position of the figure axis shifted by 8 centimeters. You can see that 120 such earthquakes, if operating in the uniform and proper direction, would be enough to align the two axes. ;-)

So far, it's pretty hard for the mankind to do something that could compete with the earthquake's effect on these orbital, spinning, and geometric parameters of the ellipsoid. Imagine the hysteria if we were able to shorten the day by a microsecond, too. The alarmists would surely blame the evil free markets for shortening of the mankind's lives by a few hours (in total). ;-)

#### 1 comment:

1. Nice article, small comment :-) Though I agree with almost all, I disagree with the last bit: if we were able to shorten a day by a few milliseconds, a person's life would not be shortened, but would APPEAR to be LONGER, by a few hours total, would it not. That is assuming we would live the same absolute length of time ;-)