The next frontiers in tsunami science
Research offers new hope - from timely forecasts to building codes and maps of potential destruction.
A quiet technological revolution is under way that could significantly improve scientists' ability to gauge undersea earthquake and tsunami hazards.
Researchers are pinging the seafloor with advanced sonar. Others are cross-examining coral to establish a region's offshore earthquake history. Still others are designing and testing sophisticated computer models for predicting how a tsunami could affect a broad segment of seacoast or a specific waterfront, block by block.
The goal is to help marine geophysicists track the restless motions of Earth's crust - especially the strain that waxes and wanes along submarine faults and plate boundaries - with a precision that only their landlubber colleagues have achieved.
The results, researchers say, could lead to more timely tsunami warnings, a clearer idea of the effect a tsunami could have on specific locations, and building and zoning codes that could significantly reduce the loss of life when a tsunami strikes.
The effort is now goaded by a sterner resolve since tsunamis swept across the Indian Ocean following an enormous earthquake off the coast of Sumatra early Dec. 26, killing well over 100,000 people.
Researchers note that an untold number of lives could have been saved if existing techniques, such as coastal tide gauges or undersea pressure sensors that detect a tsunami's passing, had been operating.
Yet, they add, warnings are virtually worthless without a local civil-defense infrastructure to receive and act on them. Indeed, reports emerging from the region over the weekend talk of misrouted government faxes, low-level officials not knowing whom to call, and governments failing to relay warnings for fear of antagonizing tourists with false alarms.
"Scientists, technologists, people who work in disaster management have been too complacent about prioritizing areas that need preemptive action," says Arthur Lerner-Lam, director of the Center for Hazards and Risk Research at Columbia University's Earth Institute. "If there's any good to come out of a situation like this, it will provide a wake-up call to take these threats seriously and make preemptive investments in warning technologies and mitigation strategies to reduce the vulnerability of populations."
Typically, tsunamis are triggered when large earthquakes alter the height of the sea floor where the quake occurs. This means that unlike wind-driven surface waves, which also can reach towering heights, a tsunami involves the entire water column from sea floor to surface. This gives it its destructive punch.
"People don't appreciate how powerful water can be," says Peter Raad, a professor of mechanical engineering at Southern Methodist University in Dallas who is working on ways to forecast a tsunami's impact on structures. A 10-foot wall of water moving at 30 miles an hour can strike with an initial force of 5 million to 6 million pounds, he says. The sustained flow behind the initial strike reaches hundreds of thousands of pounds of force.
While earthquakes are a primary source of tsunamis, undersea landslides, collapsing cliffs, and calving ice floes have also triggered them. Even human activities - from the explosion of a loaded ammo ship in Halifax Harbor during World War I to the collapse of landfill for an airport runway extension off Nice, France, in 1979, which set off a larger submarine landslide - have been responsible.
The East Coast has been hit by several small tsunamis, thought to have been triggered by submarine landslides or quakes along the mid-Atlantic ridge. The Mediterranean Sea and the Caribbean also have been hit. A subduction zone - an undersea trench where one plate of the Earth's crust plunges beneath another - stretches across the sea floor north of Puerto Rico and shows evidence of large-scale undersea landslides.
"The Puerto Rico Trench and the Scotia Trench in the South Atlantic have caused us to rethink the tsunami hazard in the Atlantic," says Jian Lin, a geophysicist at the Woods Hole Oceanographic Institution in Woods Hole, Mass.
Scientists face multiple challenges in characterizing earthquake risks on submarine faults and their potential for tsunamis. For instance, it's difficult to establish rupture histories. "Great" earthquakes, such as last month's, happen too infrequently in any one place to build a reliable statistical picture, Dr. Lerner-Lam says. "And you can't just send down a back hoe" to dig a trench along a fault and read the history written in layers of sediment.
Moreover, on land, satellite telemetry can relay data from sensors near a fault at the blink of an eye. At sea, data typically have to be recorded and retrieved later, unless sensors are linked to buoys or tied into undersea cables.
And it remains difficult to watch stress patterns change along faults in the seafloor crust - something terrestrial seismologists are doing for many land faults. Such patterns help researchers pinpoint faults likely to experience the next snap.
In addition, the time delay in refining estimates of earthquake strength can be troublesome. Fifteen minutes after the quake occurred, it was deemed strong enough to generate tsunamis - enough time for a "head for high ground" warning in many places. But it took several hours to determine that what initially had been pegged as a magnitude 8 earthquake actually was magnitude 9 - 10 times more powerful. That can make an enormous difference in how far inland waves actually go or how destructive they can be, Dr. Raad says.
For the tsunami problem itself, the most immediate payoff will come from deploying more buoys similar to those the National Oceanic and Atmospheric Administration (NOAA) is using off the West Coast and Hawaii. Pressure sensors on the sea floor are linked to the buoys, which can relay data to warning specialists on land.
Armed with that data, computer models currently running as prototypes could yield estimates of where and when a tsunami would make landfall and how far inland it would run, says Vasily Tito of NOAA's Pacific Marine and Environmental Laboratory.
Meanwhile, researchers are testing new high-frequency sonar techniques to monitor large-scale shifts in strain patterns around submarine faults and to "dig" into sea floor sediment for evidence of breaks in the layers. The breaks would reveal the sizes and relative history of temblors at a given location. Core samples would then allow scientists to date the quakes.
Others are working on how to minimize tsunami fatalities. With colleagues from six universities around the US, Raad is developing computer -simulation capabilities that will allow for more effective tsunami building codes and zoning practices. He notes that merely placing parking lots on a waterfront gives a tsunami steel-and-rubber ammunition to knock out buildings that might have withstood the tsunami itself.
Within the next five to 10 years, he says, the group hopes to have developed tools that will allow planners to play "what if" as they look for ways to reduce vulnerability - with scenarios tailored to the layouts of communities, undersea geography, and the direction from which a tsunami strikes.