Monday, August 29, 2005

Shifts in the Magnetic Poles…

As many of us know, there are two kinds of poles for the Earth, the Magnetic poles and the Geographical poles. Although the location of the geographical poles remains constant, those of the magnetic poles do not.
Scientists believe that they have discovered the possible reason for these shifts, being, that the Earth’s core rotates faster than its surface, by about 0.3 to 0.5 degree per year.

Structure of the Earth
Earth’s iron core consists of a solid inner core about 2,400 kilometers in diameter and a fluid outer core about 7,000 kilometers in diameter.
Whenever an earth quake occurs, the shock developed travels in the form of waves called seismic waves. These waves are of three kinds and travel with different velocity in mediums with different densities. Scientists have long been studying the anatomy of earth quakes using devices called Seismograms which record the intensity and the origin of an earth quake. Several hundreds of seismic stations equipped with similar devices are located all around the globe to constantly monitor and study the tectonic and crustal movements.

The unnatural phenomenon
Researchers reported observations of 17 sets of similar seismic waves – called waveform doublets – from earthquakes occurring in the South Sandwich Islands region off the coast of South America. The doublets, which were recorded at up to 58 seismic stations in and near Alaska with a time separation of up to 35 years, allowed the researchers to detect temporal changes along the sampling paths.
The similar seismic waves that passed through the inner core show systematic changes in travel times and wave shapes when the two events of the doublet are separated in time by several years. The only plausible explanation is a motion of the inner core.

Explained
The most likely explanation for why the inner core is rotating at a different speed is electromagnetic coupling. The magnetic field generated in the outer core diffuses into the inner core, where it generates an electric current. The interaction of that electric current with the magnetic field causes the inner core to spin, like the armature in an electric motor.
The fluid outer core decouples the solid inner core’s movement from the mantle. Because the fluid outer core is not very viscous, frictional drag is small.
The inner core plays an important role in the geodynamo that generates Earth’s magnetic field, which in turn could be the reason for varying magnetic poles.
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