Network Of Underwater Sensors To Measure Dangerous Tsunamis In Real Time

Tsunamis -- giant seismic sea waves, sometimes as high as a five-story building -- can crash against coastal communities, kill thousands of people instantly and devastate property. They are produced by undersea earthquakes, or landslides or volcanic eruptions.

"From locations all around the Pacific, we cannot now predict what kind of tsunamis form, where they are from, and how to accurately gauge their magnitude," said Philip L.F. Liu, Cornell professor of civil and environmental engineering. "With a new array of instruments, we can start to research tsunamis and perhaps we'll be able to save lives."

Liu explained that tsunamis travel at speeds close to 600 miles an hour in the open ocean and at 100 miles an hour closer to the shore, and they are still difficult to predict. Thus, last spring, scientists gathered at the Natural Hazards Mitigation Program workshop, in Santa Monica, Calif., sponsored by the National Science Foundation, and formulated objectives to study tsunamis.

The report from the workshop, "Tsunamigenic sea-floor deformations," appears in the journal Science (Oct. 24, 1997). It was prepared by Liu; Costas Synolakis, of the University of Southern California; George Carrier, of Harvard University; and Harry Yeh, of the University of Washington.

One initiative of the workshop, now being reported, is that bottom-pressure recorders (BPR's) and seismic instrument arrays for real-time monitoring of tsunamic development will be deployed by next year. The instruments will be placed by the National Oceanic and Atmospheric Administration (NOAA) in strategic parts of the Pacific rim, such as south of the Aleutian Islands chain and along coastal areas of Asia.

Another initiative from the workshop was to study sea-floor deformation characteristics, obtained from seismic data, during undersea earthquakes that turn into tsunamis.

Liu explained that these natural, hydrologic terrors have devastated many parts of the world. The 1960 tsunami, resulting from an undersea earthquake near Chile, killed 5,000 people, and the tsunami traveled at airplane-like speed through the water to the Hawaiian island chain, where it killed 61 people and caused millions of dollars in property damage. After striking Hawaii, the tsunami continued nine more hours, finally striking Japan and killing 150 people.

The tsunamis do not occur after every oceanic earthquake, said Liu. For example, if the sea floor shakes from side-to-side, then the effect on tsunami will be minimal. But, if there is an up-and-down motion, a tsunami develops. Liu said seismologists now detect several minor tsunamis annually.