Earthquakes and Magnetic Stripes on the Sea Floor

23 Feb 2012

Presentation of science to Joe Public is often jazzed up - in books, on TV and in museum displays and the classroom. Take, for example, sea floor spreading (see page 3 at We are all familiar with the pattern of stripes on the Atlantic sea bed radiating out from the Mid Ocean Ridge. There are diagrams and drawings that have been somewhat set to create that piano key pattern of striping. The mapping of the sea floor was largely done by surface vessels  and the result was really quite chaotic, jerky, and broken lines were the rule rather than the smooth thick and prominent lines as we are generally shown by those that would teach us the facts of science.

It is a hypothesis that the magnetic stripes record reversals of the earth's magnetic field. Submersibles were used at one location in the Pacific and they showed that the magnetic anomalies the scientists onboard looked at mostly went down some 3.5 km and magnetism obviously went even deeper than that - but was out of range. This required an explanation as it was unexpected. It was proposed that lava extruded not only from the centre of a spreading ridge but along its sides too. The clear pattern of reversals as assumed in Plate Tectonics Theory, the consensus model, may not strictly be true as there are numerous small scale anomalies that are perhaps related to changes in the intensity of the geomagnetic field rather than its polarity.

The december of 2004 Boxing Day Sumatra earthquake (and tsunami event) is thought by some to have affected the core-mantle boundary leading to a geo-magnetic 'jerk' (quoting a paper in Space Science Review 155 (2012)'Geomagnetic Jerks: Rapid Core Field Variations and Core Dynamics'). The author of the New Geology piece is at pains to promote his Shock Dynamics Theory of rapid movement of the continents and rapid mountain building events but leaving that aside the consensus model does seem to be somewhat minus the role of the Sun's magnetic field within the Solar System. The existence of different polarity zones at different depths suggest the source of magnetic anomalies lies in deeper levels of ocean crust not yet drilled or dated and that the anomalies may well have a connection with seismicity rather than reversal episodes.