January 18, 2005

Chicago researchers explain the science of tsunamis

Nearly three weeks after the devastating tsunami rocked South and Southeast Asia, international leaders are reviewing the grim tragedy and looking for lessons that might limit the destruction of future tsunamis.

Doug MacAyeal, a professor in the Department of Geophysics, said that even with existing technology, optimistic scenarios require a number of carefully coordinated steps. According to MacAyeal, if the precipitating event is an earthquake, scientists must first locate the earthquake by rapidly collecting and analyzing seismographic data. Armed with a precise origin, geoscientists and oceanographers then can determine wave direction and speed.

While tsunami travel is understood very precisely—MacAyeal said he can "write the equations in five minutes" for tsunami statistics­­—their creation is not yet an exact science. Ideally, according to MacAyeal, wave characteristics are determined from the coordination of computer models and real-time data from a tsunameter network.

Armed with landfall predictions, scientists issue alerts that are passed along to at-risk communities through civil communication networks. Internet and satellite-based telecommunications can easily outrun a 747, and this save lives-given a well-coordinated system.

Tsunami detection and warning systems, already in place in other parts of the world, have leaped to the forefront of international dialogue: The Prime Minister of Thailand established an investigatory panel; the UNESCO announced plans for a $30 million global detection system by 2007; and President Bush announced an extension of the US's resources. Though well intentioned, there are still many obstacles to tracking and predicting tsunamis.

Tsunamis, by definition, are not self-generating phenomena. The most powerful earthquake in 40 years caused the December 26 tsunami, but other sources include landslides, underwater volcanic eruptions or large meteorides. Each of these events could displace enough water to create a deep ocean wave, the early phase of a deadly tsunami. Moving as fast as a Boeing 747 and covering hundreds of square miles, deep ocean waves are notoriously difficult to detect, since they're only a few feet high.

Even an experienced mariner sitting atop a deep ocean wave is unlikely to notice anything out of the order. The only possible witnesses of a deep ocean wave are expensive and sophisticated tidal gauges or underwater tsunameter sensors developed by the National Oceanographic and Atmospheric Administration (NOAA).

While working in Hawaii at the Pacific Disaster Center (PDC), U of C Ph.D. candidate Leila Zajac was told to run for high ground if she saw an empty bay. Zajac said that that was an example of an early sign of a tsunami: a rapidly falling tide. As the deep wave reaches shallower water, it slows and grows. A given wave's final speed and height depends drastically on the underwater geography close to landfall.

Cost is the first hurdle for a warning system to be implemented in the Indian Ocean. In the Pacific, high costs are outweighed by high risk and regional economic wealth: More than 90 percent of the world's tsunamis and underwater earthquakes threaten US or Japanese territories. But before December 26, only a fringe group of scientists argued that a tsunami detection system in the Indian Ocean would be politically or economically feasible.

The second hurdle is uncertain data. For every clearly disastrous tsunami, there are legions of lesser waves and wave-producing events that pose uncertain threats. Scientists believed in 2003, a 7.8 magnitude underwater earthquake would produce a tsunami threatening the Aleutian Islands. Contrary to computer models and oceanographers' predictions, the earthquake produced no tsunami.

Tragic accounts from December 26 highlight the persistence of communication gaps. Disaster managers in the Pacific struggled in vain to warn their Indian Ocean counterparts, limited by a lack of telephone numbers. Zajac said that for developing island nations, there may be no phone numbers, a difficulty she and her co-workers at the PDC experienced with parts of French Polynesia. Even after a call is completed, gaps in local infrastructure are a formidable problem: Having seen the coming wave, a deputy mayor in Indonesia could only run down streets, banging on doors and shouting through windows.

In a more fundamental sense, even the best systems cannot guarantee safety: The recent tsunami's epicenter was so close to landfall that more than 45,000 Indonesians were killed less than a half hour after the quake. The time-lag issue is even more problematic for non-seismic events like landslides and meteorides.

Though well intentioned, tsunami warnings systems are no silver bullet. Dense and underdeveloped seaside communities are inherently at-risk.