The National Science Foundation has awarded Grilli a $204,000 grant to further his research and develop a computer model that will simulate the effects of underwater landslides. The model will be used to better predict the impact of tsunamis around the world and help prevent the loss of life that often results from the massive waves.
Commonly called tidal waves even though they have nothing to do with the tides, tsunamis are usually created by earthquakes that occur at the bottom of the ocean. The shifting ocean bottom causes the movement of seawater over large distances.
"In deep water the wave may only be a foot high, something a boat wouldn’t even feel, but it can travel as fast as a jet across the ocean," explained Grilli. "As the wave moves into shallow water it slows down and grows taller. It could be 50 or 60 feet tall or more by the time it reaches shore."
Grilli and other scientists have recently shown that underwater landslides caused by earthquakes often contribute significantly to the size and intensity of tsunami waves. By studying the topography of the ocean bottom where earthquakes have occurred, scientists have explained why some modest earthquakes have resulted in massive tsunamis.
"In an unstable area where there are large accumulations of sediment, like along the continental shelf, an earthquake could cause a major landslide. And that combination of events can cause huge tsunamis," said the Narragansett resident. It is now believed that 60 percent of all major tsunamis are caused by the combined energy of an earthquake and landslide.
Grilli notes that tsunamis occur all the time – perhaps thousands each year, the majority in the Pacific Ocean – but most are too small to notice. Two or three times each decade, though, large tsunami waves kill hundreds of people, most recently in 1998 when 2,000 people were killed in Papua, New Guinea.
"Those we worry most about occur in shallow water close to shore, because they hit the coast quickly without any warning," he said. "And if they hit in low-lying areas, the wave can propagate far inland and cause serious flooding and loss of life."
Grilli’s tsunami prediction model is designed as a hazard assessment and mitigation tool. "If you can predict where they are most likely to occur and predict their intensity and speed, then you can mitigate potential damage."
The computer model he is creating is actually a series of models, based in part on the results of past tsunamis and on experiments conducted in the URI wave tank. One model will examine how earthquakes make sediments move, while another will focus on the physics of the resulting movement of water. Grilli will also create a model that predicts the flooding that will occur from the wave. All the models will be used in conjunction with a Geographic Information System (GIS) map.
When the model is complete in the fall of 2003, it will be made available on the internet for use by organizations like the Tsunami Warning Center in Hawaii, the Federal Emergency Management Agency, and the worldwide community of tsunami researchers, hazard assessment agencies, and emergency preparedness professionals.