In an article in the swedish news paper Dagens Nyheter (News of the Day) they've talked to some scientists at the Chalmers Institute about how huge earthquakes, like the one recently in Chile which measured 8,8 on the Richter scale, actually change the axis of the earth and thus the duration of the earth day. Of course we're not talking about anything that will ever be noticed by the lay human in thousands of years. Apparently the above mentioned earthquake had shifted the earth axis by approximately 8 cm and shortened the duration of the earth day by 1,2 millionth of a second. WHat happens is simply that the earth quake reorganizes the materia in the Earth to make it smaller or larger (mostly smaller), and this in turn makes Earth turn faster, just like if you spin and spread or pull in your arms.
Why even bother about measuring such small changes? It obviously won't turn into the Apocalypse for humanity any time soon. Apparently it matters when sending stuff, to date mostly satellites and probes, into space. Apparatus used in GPS systems use the parameters of Earth to tell people where they are, and even small differences can turn into huge errors back on Earth. Just imagine driving right into someones living room just because your GPS is misinformed by 8cm!
And for space probes that are sent off way into space, few milliseconds off in the Earth Axis data could turn into driving kilometers off once you reach Mars. What seems like small errors here on Earth will turn huge over the course of very long distances. Something quite worth to think about once we decide to colonize space.
I thought this was really interesting because I had never heard anything about earth quakes also having this huge impact on Earth, beside the already huge impact it has on human lifes wherever it occurs. These are changes on a cosmic scale! Once you know of it you realize that it is quite logical of course, just nothing you ever think about. Although earth quakes never happen in sweden (I do not count the occassional, lame shrugs that barely shakes a block of houses as real earth quakes) it makes you think about how things that happen anywhere on earth really affect everyone on it. You easily get the feeling that we're isolated from other countries just because we don't see them, and somehow I think it is important that we think "This affects me too" when distaster strikes on the other side of the Earth.