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6.8 Honshu Earthquake | May 07, 2008
Today at 1:45 in the morning local time a magnitude 6.8 earthquake struck off the coast of Japan, light shaking was felt in Tokyo and other coastal areas, though no major damage was reported. Bulletins from the West Coast/Alaska Tsunami warning center said no tsunamis were expected along the west coast. A series of strong aftershocks continues to rock the region and none of these are expected to generate tsunamis either. Seismometers around the world, including South Carolina are recording the passing of these great earthquake waves.
Seismograph of Earthquake waves passing through New Hope, SC From the Ceri Memphis and USGS websites.
This was a shallow thrust earthquake (meaning the fault was at a low angle to the surface and the two sides moved towards each other). Japan is prone to these types of earthquakes because the Pacific plate is moving towards and under Japan. As the two plates move towards each other and Japan overrides the Pacific plate the two sides occasionally get stuck. The movement around the stuck location continues and energy builds up on the stuck area as the rocks bend against each other. When that stuck area lets go rocks snap back into their original shape and release the energy in the form of shaking (like stretching a rubber band and then suddenly letting it go).
Unlike Japan, South Carolina’s earthquakes are not caused by two plates moving past each other, instead they are caused by fractures within the North American plate moving slightly and getting stuck. The fractures within the plate are moving slightly because of the overall push on the edge of the plate from the Mid-Atlantic ridge. South Carolina has a number of these fractures at just the right angle such that the push on the plate makes those fractures move and get stuck.
Curator: hallcr@cofc.edu
