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The earthquake in Chile and the polar axis: analysis from our centre in Matera

No major shifts so far at the ASI Space Geodesy Centre

As with any event that produces a movement of the Earth’s mass, the recent, extremely violent earthquake in Chile also caused a shift in the Earth’s axis of inertia with respect to its rotation axis. However, it should be pointed out that much larger movements occur continually, above all as the result of atmospheric and oceanic circulation: the difference is that a seismic event is of a "transient" nature, whereas atmospheric and oceanic circulations have much longer timescales.

Using data from the International Laser Ranging Service, the global system which uses lasers to measure, with millimetre resolution, the distance between a network of stations on Earth and reflectors on satellites, the ASI Space Geodesy Centre in Matera (which has been the Official Primary Combination Centre since 2004) calculated the residual motion of the pole in comparison with values from immediately before the earthquake. Preliminary results do not show significant disparities, i.e. greater than one millisecond of arc, equivalent to about three centimetres. Corresponding research following the 2004 Sumatra earthquake showed a very clear difference of about two milliseconds of arc, equivalent to about six centimetres. However, it is important to wait for the results from other geodesic networks, based on independent observational techniques, before drawing conclusions; estimates of atmospheric and oceanic angular momenta supplied by specialised international research centres will give precious interpretative help in separating the seismic effect from phenomena of a different nature that interact with it.

This evaluation differs from those obtained using theoretical models of the planet (such as the one produced by the Jet Propulsion Lab in Pasadena, California) which can estimate the extent of a shift on the basis of geophysical and seismological data. This is the type of calculation used in meteorological forecasts, which are based on data observed before a particular date and on theoretical models of how atmospheric phenomena develop.

Giuseppe Bianco,
Centro di Geodesia Spaziale  - Matera
Agenzia Spaziale Italiana
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