TSUNAMI WARNING SYSTEMS CONTINUE TO IMPROVE
By Cliff Harris
‘Tsunami’ is a Japanese word meaning "large waves in harbors." This description is a particularly apt one, especially after seeing the tremendous amount of damage this past March 11 from the killer tsunami that occurred some 30 minutes after the record 9.0 earthquake in the bays and harbors of northeastern Japan that killed at least 10,000 people.
Most tsunamis have occurred following strong earthquakes along the so-called ‘Ring of Fire’ in the Pacific Ocean regions. A section of the ocean floor shifts radically, either up or down, just prior to a catastrophic tsunami. Submarine landslides also occasionally cause tsunamis, but these are rare.
When the ocean floor suddenly drops as an earthquake shifts the sea vertically, it has an effect similar to when a plug is pulled from a bathtub drain. The downward movement of the sea floor into the ‘hole’ before it rises sharply back to the surface creates the deadly tsunami wave.
This displacement of a vast quantity of water sends huge waves of great force radiating from the epicenter of the strong earthquake in all directions. However, in most cases, it’s almost impossible to see these waves until they crash upon the shores causing enormous amounts of damage like they did in Japan.
At the same time, knowing the depth of the ocean through which the tsunami is moving, makes it possible to predict just when it will arrive at a given point.
The speed of the tsunami is well known. It travels at between 500 and 600 miles per hour, near the speed of a jet aircraft.
There are actually two main facts that scientists must determine after a strong earthquake in order to predict the exact cause of the tsunami.
First, these scientists must know the precise epicenter of the quake and the depth of the ocean over which the tsunami is traveling. Recent extensive soundings in the Pacific have shown an average ocean depth of about 14,000 feet.
Second, by multiplying the average water depth by the acceleration of gravity, thirty-two feet per second, and taking the square root of the sum, the specific speed and the direction of its path can be determined.
For example, a huge undersea earthquake in the Gulf of Alaska could be expected to produce a tsunami that would reach San Francisco in about 5 hours. An earthquake centered offshore from Los Angeles would reach Cape Horn in the southern tip of South America in approximately 17 hours.
Since the late 1940s, this knowledge has led to an advanced tsunami warning system throughout the Pacific. Following the deadly May 1960 tsunami in Hawaii, which killed 61 people in Hilo on the eastern side of the Big Island, scientists have been issuing wave-size predictions for particular regions. This helped save many lives following the huge earthquake in Alaska on Good Friday in 1964. Even the recent tsunami in Japan would have seen a much higher death toll without the much improved warning systems. Some people had only minutes to reach higher ground.
In our current cycle of increased earthquake activity in the Pacific ‘Ring of Fire’ regions, we could see at least a couple of more disastrous tsunamis in the next decade, possibly even along the western U.S. coastlines. Stay tuned.