Superstition: Belief in the Age of Science by Robert L. Park

Author:Robert L. Park [Park, Robert L.]
Language: eng
Format: epub, pdf
ISBN: 9781400828777
Publisher: Princeton University Press
Published: 2008-01-25T06:00:00+00:00

THE TECTONIC PISTON

For scientists, whose business it is to understand why things happen, natural disasters become experiments. While religious leaders pondered questions of divine punishment and whether humans are subjected to testing by some supernatural intelligence, geophysicists were studying the data from seismic stations around the world. A gigantic earthquake centered in the Indian Ocean about a hundred miles west of Sumatra was the proximate cause of the tsunami. But what had caused the earthquake?

It was one of the most powerful earthquakes recorded since the invention of the modern seismometer. We live on the thin, solid crust of a molten planet that has been cooling since it was formed 4.5 billion years ago. The crust is broken up into tectonic plates, great slabs of rock that push against one another along fault lines as Earth continues to cool. Occasionally the plates fracture or slide over one another. Earthquakes are abrupt movements of these tectonic plates along the fault lines.

Like a stick bent until it snaps, elastic energy built up between two major plates in the Indian Ocean was suddenly released as one plate abruptly slid over the other. Not every quake below the ocean results in a major tsunami, but because one tectonic plate was forced upward by the movement, it acted like a giant piston, pushing up a huge volume of water. The water spread out across the ocean in concentric ripples, like pouring a pail of water into a pond.

Tectonic earthquakes are an inevitable natural phenomenon. On a smaller scale, they occur somewhere in the world every day. This one was simply much larger than most. Nevertheless, because it was centered far out at sea, the earthquake itself caused little damage. Although the waves were very high, they were also very wide, so that ships at sea experienced only a gentle rocking as the tsunami passed beneath them. The devastation came when the waves reached the shoreline.

The tragedy was that in the time between the earthquake and the arrival of the tsunami at Banda Aceh, there was plenty of time for people to seek higher ground—if they had known. The shock wave from the quake, traveling at the speed of sound through the Earth, was detected by seismometers around the world, but while each seismic station knew there had been a major earthquake, they did not immediately know where. All they knew was the time when the shock waves arrived at their seismometer.

Actually, two shocks are recorded: the P-wave, or compression wave, that travels through the Earth, and an S-wave that travels along the surface like a wave on the ocean. The P-wave travels faster. From the separation between the P and S waves, the distance from the seismometer to the epicenter can be calculated. If the distance from three widely separated stations is known, scientists can pinpoint the location of the quake.

The most modern seismic stations are located around the Pacific Ocean: Japan, Hawaii, and the west coast of the Americas in particular. The rim of the Pacific has a history of severe volcanic eruptions, earthquakes, and tsunamis.

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