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"On This Day" In Engineering History

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March 9, 1957 - Andreanof Island Quakes

Posted March 09, 2007 6:00 AM by julie

March 9, 1957: The Andreanof Islands Earthquake

Today marks the 50th anniversary of the Andreanof Islands Earthquake off the coast of Alaska. With a magnitude of 9.1 on the Richter scale, this earthquake was centered at 51.5° N and 175.7° W, just south of the Andreanof Islands, a subgroup of the Aleutian Islands. Local damages from the Andreanof Island Earthquake included the destruction of two bridges on Adak Island, as well as ruined houses and roads. Mount Vsevidof, a volcano that had been dormant for 200 years, also erupted as a result of the quake. Most significantly, the Andreanof Islands Earthquake resulted in a 15 - 16 m tsunami that, in addition to hitting local coastlines in the Aleutians, continued on to Hawaii and caused over $5 million (USD) worth of damages. Villages on the Hawaiian islands of Oahu and Kauai were destroyed before the tsunami continued on to San Diego Bay, California; Chile; El Salvador; Japan; and many other areas of the Pacific Ocean. Amazingly, no lives were lost in either the earthquake or the tsunami.

Early tsunami protection and detection systems were very limited in 1957. Primitive protection systems included coastal defenses such as concrete sea walls to blunt the impact of waves, and gates that would slam shut to protect harbors. Unfortunately, however, these systems did nothing to warn scientists about tsunamis. The primary predictor of a potential tsunami was the seismometer, an instrument which would issue a warning when a large, shallow earthquake was detected under the seafloor. The problem with these early tsunami detection and warning systems was simple - not every earthquake leads to a tsunami. Although Hawaii had established the Pacific Tsunami Warning Center in 1948, high levels of inaccuracy had led to costly evacuations.

Modern tsunami detection systems use sensors that sit on the seafloor and can detect a tsunami passing overhead. Japan, for example, laid a cable containing these sensors outwards from its coastline. Since the tsunami of December 2004, the U.S. National Oceanic and Atmospheric Administration (NOAA) has decided to add bottom sensors to its warning system, too. These sensors operate by sending a signal to an attached buoy which then relays a message via satellite when a tsunami is detected. With this modern tsunami detection system, the sensors could give potential victims hours of warning time, depending on where the tsunami originates.

Fortunately, the tsunami caused by the Andreanof Islands Earthquake did not cause any casualties. Subsequent research and development in tsunami detection systems has led to advanced technologies that will hopefully help to avert disasters like the 2004 tsunami that struck the South Pacific.






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