Of the axis of the Earth and the earthquake in Chile

It will be you read up to the satiety that the recent earthquake in Chile has provoked a change in the axis of rotation of the 8 cm Earth and a reduction of the day in approximately 1,26 microseconds. The same way, although with less aftereffect mediática, numbers happened for the earthquake of Sumatra of the year 2004 of 7 cm of deviation of the axis and 2,7 microseconds of reduction of the day.
Those that they follow this blog will not turn out to be strange to them that it has looked at anything beyond the news I hope there was locked up cat.
The result is that perhaps the numbers are true. Or perhaps not. The first thing that is convenient to know (something that all the means have not made clear) is that the above mentioned changes have not measured themselves but there are results of a computer simulation. Since we have already commented other times, the accuracy of the simulations depends on multiple factors difficult to control, especially in very complex models like this one. Also, on having been simplifications of the reality, his results do not reflect necessary what really it has spent but only one more or less good approach.
They say that the Earth turns something more quickly and that his axis has moved due to the earthquake of Chile. This can be true or perhaps not. The above mentioned effects are not verifiable today because they are much underneath of our measurement capacity and, a little that they not all have said, there are no real information but result of a computer model.
How much of good? Since it is not possible to know since at present the rotation of the Earth can only measure itself to an approach of approximately 20 microseconds. Therefore, the empirical assertion of the reduction of the day is impossible for the time being, the same as the 8 cm supposed change in the terrestrial axis since the models work with an average error of approximately 50 cm.
I want to make clear that this post is not to criticize the news but to insist once again on the absolute need to distinguish between information (real measurements) and results of simulations. The above mentioned are affected by multiple suspense sources so that the results should always happen with an estimation of the same one. Also, I will give information to value if these 8 cm are something important or not,
The author of the simulations is Richard Gross, a geophysical one of the JPL with a wide trajectory in this type of works and a specialist in the factors that they affect to the terrestrial rotation. His models base that the rotation speed depends on the masses distribution both in the surface and inside the Earth. In this sense, the proper ambience influences the above mentioned rotation and Gross mentions that the days throughout the year change about a microsecond due to home changes in the share-out of the air masses.
What leaves something to me out of game is that Gross does not mention the due movements of the badges adrift continental, slightly much more important than the earthquakes or the ambience. Let's suppose that we have a recipient GPS between the hands. When we look at his screen we see three position information: latitude, length and height. Logically this information happens with regard to a reference system: to say 40th of North latitude supposes knowing where there is the origin of latitudes (the Ecuador); the same way, to say 10th of length West supposes knowing where there is the origin of lengths (the midday origin).
The GPS uses a reference system called WGS84 (World Geodetic System 1984). WGS84 is an artificial construction formed by three axes of coordinates and a surface of revolution called ellipsoid that comes closer at the average level of the oceans of the world.
Three axes it allows to give a position in the space and the ellipsoid is used like surface of reference to the heights. The exact definition of these elements is essential to know to what there refer the geographical coordinates or any others that we could use. The principal characteristics of the WGS are (be fixed in the italics):

• three Cartesian axes and the ellipsoid are geocentric: they have his origin in the center of masses of the Earth (including seas and ambience).
• the axis Z coincides with the axis of rotation of the Earth since International Reference Pole points to.
• the axis X points at the 0th meridian of length also known as meridian of Greenwich.
• the axis Y is orthogonal with the previous ones and with the Xth it defines the equatorial plane.

The interesting of this matter is that none of the previous references is fixed: neither the center of masses, nor the Pole nor the midday zero. Greenwich and the meridian that it defines are on a continental badge that moves, then his position with regard to the rest of the world changes continuously. Also we know that the axis of rotation of the Earth is not fixed but it ranges in the due time, between other causes, adrift continental (to see in the end). Finally, the center of masses of the Earth is not also in the same point but it changes as everything moves in the surface. The consequences are those that they can suppose: the poles, parallels and meridians are not stationary with regard to any point in particular of the Earth.
You tackle in the area of South America (of Wikimedia Commons)
In effect, owed adrift continental, the different parts of the world move and several centimeters change relative position a year. The Meridian and the International Pole of Reference become stationary for agreement with regard to the average of the above mentioned movements and his position has to recalcularse and redefinirse of continuous form. The magnitude of the movement is not spectacular but undoubtedly more influential than the atmospheric changes or the earthquakes (that are only movements in the area of friction of badges, to see top figure). For example, in England the latitudes and lengths WGS84 change to a constant valuation of approximately 2.5 cm a year in direction NE. Other parts of the world as Hawaii or Australia move about 10 cm a year.
That's why, when they hear or read that thing about 8 cm of change do not fall down in the temptation of believing that if it was not that's why we would live in a calm and static way. Further at all of the reality, here nothing remains a lot of time neither in the same place, or the axes, or the masses, or the rotation of the Earth, or us. For addition, they will see in the lower figure that the Pole is moving continuously and his place has changed more than 11 meters in the last year, a number that allows to do to itself an idea about which we are speaking.
Movement of the North Pole in the last year. The units are thousandth of second of arch (more) where 1 more is equivalent approximately to 3 cm (available in Earth Orientation Centre).
More wood:
As this was ending there appears in the "news" of Earth Orientation Centre a note that comes to the hair:

The earthquake of Chile of February 27, of magnitude 8.8, has caused detectable effects neither in the place of the pole of rotation nor in the speed of the same one.

The previous thing does not mean that the effect does not exist but, as he was commenting more above, it is not verifiable because the "normal" changes are much bigger and because the resolution of the methods of measurement is ruder enough than the effect that he wants to measure himself.