[Marxism] To Carlos A. Rivera

acpollack2 at juno.com acpollack2 at juno.com
Mon Dec 27 16:18:35 MST 2004


"It's a matter of resources," says Charles McCreery, director of the Pacific Tsunami Warning Center in Ewa, Hawaii. "We know that tsunamis can occur in all the world's oceans, but we have the most organized warning system in the Pacific because that's the most seismically-active region. In other places tsunamis are much less frequent, so it's been hard to find resources for them."

CNN this afternoon quoted a scientist saying the money for an early warning system -- not GPS, but buoys, radios, people to staff them -- is worth spending. This gets, weirdly enough, back to the question of social security insurance, with small s's and i's. It would cost millions, and perhaps only be used once every few decades -- but work that out in dollars per life...
     
December 27, 2004 
 
The Science of Tsunamis

The Indian Ocean Has Few
Of the Early-Warning Systems
That Ring the Pacific Ocean
By SHARON BEGLEY and GAUTAM NAIK 
Staff Reporters of THE WALL STREET JOURNAL
December 27, 2004; Page B1

Experts, let alone victims, never saw it coming.

Before yesterday, there had never been such a devastating tsunami -- a seismically-generated ocean wave -- triggered by an earthquake beneath the Indian Ocean. As a result, Southeast Asia had nothing like the tsunami-warning system that is in place along the Pacific coast. Nor has a quake-generated tsunami started in the Indian Ocean ever crossed the entire Indian Ocean basin, as yesterday's did, reaching from Sri Lanka, Indonesia and Thailand all the way to the east coast of Africa.

"In records going back to 1509, most tsunamis spawned in the Indian Ocean have had only one run-up," or have hit in only one place, says oceanographer Eddie Bernard, director of the Pacific Marine Environmental Laboratory, Seattle, part of the U.S. Department of Commerce. "There do not seem to be any tsunamis that were Indian Ocean-wide."

That largely reflects the fact that 95% of the world's earthquakes occur in the Pacific Ocean, and tsunamis almost always are triggered by earthquakes. The Pacific Rim is ringed with early-warning systems intended to detect an imminent tsunami in time to allow people to flee to higher ground.

The International Tsunami Information Center, for instance, established in 1965 by an agency of UNESCO (the United Nations Educational, Scientific and Cultural Organization) to improve tsunami preparedness, focuses on nations that rim the Pacific. In the U.S., tsunami research, modeling and warning programs are limited to the Pacific coast, Hawaii and Alaska. Countries bordering the Indian Ocean have virtually no early-warning system.

"It's a matter of resources," says Charles McCreery, director of the Pacific Tsunami Warning Center in Ewa, Hawaii. "We know that tsunamis can occur in all the world's oceans, but we have the most organized warning system in the Pacific because that's the most seismically-active region. In other places tsunamis are much less frequent, so it's been hard to find resources for them."

The earthquakes that cause tsunamis almost all occur where tectonic plates -- shards of the earth's crust -- meet. Magma rising up from deep within the Earth causes the plates to move. Along faults such as California's San Andreas, the plates are slip-sliding past each other, occasionally getting stuck and then suddenly jerking forward again -- producing an earthquake.

The wall of water that devastated the coasts of Sri Lanka, India, Indonesia and Thailand yesterday was born where two tectonic plates behave differently, in what is called a subduction zone. About 6.2 miles beneath the Indian Ocean, one such plate, called the India plate, is moving slightly more than two inches a year toward the northeast, according to the National Earthquake Information Center, Golden, Colo. Where it meets another plate, called the Burma plate, it dives under, or subducts. Yesterday, a section of the India plate about 620 miles long slipped under the Burma plate, says the National Earthquake Information Center. That caused the sea floor to lift up and then drop down again, with catastrophic results.

"A zone where one plate is slipping under another is the most dangerous kind of plate boundary for generating tsunamis," Dr. McCreery says. The diving plate causes the ocean floor to deform, "pushing it up and then down again," he says, carrying the entire water column with it. That has occurred before in the Indian Ocean, but never with this magnitude.

"From the historical record, it looks like there were two tsunamis originating in subduction zones in the Indian Ocean in the 1800s, and another in the mid-1990s, but these had purely local effect," he says.

A quake that measures 9.0 on a scale of earthquake intensity brings devastation that makes everything else in the historical record pale. "The massive vertical rupture in the sea floor acted like a gigantic wave machine, displacing a huge amount of water," says seismologist Brian Baptie of the British Geological Survey.

 
In the deep ocean, such undulations generated by the "wave machine" typically aren't even detectable by ships. The wave crests often measure less than three feet high and are hundreds of miles apart, so sailors sense nothing amiss and typically don't even know that they are riding atop a growing tsunami. Because the crests are so small and infrequent, it isn't even obvious how fast the tsunami is traveling in the deep ocean: at the speed of a jet, about 500 miles an hour.

Ships and sturdy boats sailing in deep waters can usually ride out a tsunami, Dr. Baptie says. In shallower waters, though, the tsunami usually wins, he says, adding that in the past, tsunamis have been known to deposit ships located in coastal waters hundreds of meters inland.

Once the tsunami reaches a coastline it slows down and begins traveling at about the speed of a regular wind-generated wave, perhaps 20 to 30 miles an hour. But now it is enormously more dangerous than it was in the open ocean. As the waves slow down near land, all the energy of the wave gets compressed into much less depth. That causes the wave height to increase.

"The tsunami looks less like a regular wave than like a flash flood or a fast-rising tide, with the ocean rising," Dr. McCreery says. Tsunamis rarely "break" the way regular ocean waves do; the wall of water just barrels onto land, petering out only as it reaches far inland.

Scientists have developed a precise formula to predict how a wave will behave once it reaches the coast. The speed of the tsunami is proportional to the depth of the ocean through which it travels; specifically, it equals the square root of the gravitational constant (9.8 meters a second) times the depth of the ocean in meters. That formula allows scientists to warn coastal residents when a tsunami is to strike.

Because the Pacific Ocean is so well instrumented, with seismic detectors scattered throughout the basin, "tsunami warning centers can locate an undersea earthquake within three to 15 minutes after it occurs and assess the tsunami threat within minutes," Dr. McCreery says.

A tsunami that has traversed an entire ocean basin, called a deep-water tsunami, also slams into the coast like a very strong, very fast tide, as if the whole ocean is rising. Tsunamis typically hit in a group of three to 10 waves, separated by troughs, Dr. Bernard says.

Because the triggering mechanism -- be it an undersea earthquake, volcano or landslide -- moves such an immense volume of water up and down, tsunamis can propagate across entire ocean basins: they have been known to travel across the entire Pacific Ocean in less than 24 hours. Although a single quake produces only one tsunami, aftershocks can cause smaller ones.

In the worst tsunamis, a wall of rushing water called a bore forms. It arrives onshore packing huge destructive power. Right behind it is a deep, fast-moving flood that can sweep away almost anything in its path. In 1755, a tsunami originating with an earthquake in the Atlantic Ocean obliterated Lisbon and surrounding areas, killing 60,000 people. The 1883 tsunami triggered by the eruption of the Krakatoa volcano on an island off Indonesia killed an estimated 36,000 people. Although tsunamis from Krakatoa reached as far as Australia and Hawaii, the waves were not very tall and therefore did very little damage. Almost all the devastation was confined to Indonesia's Java and Sumatra. The most recent catastrophic tsunami, in 1998 off Papua New Guinea, killed an estimated 2,200 people.

Although nothing can be done to damp, let alone stop, a tsunami once it has been triggered deep under the ocean, coastal residents can watch for signs that one is imminent. The earthquake that caused the tsunami also can cause nearby ground to shake, Dr. Bernard notes (although many of the regions struck yesterday were too far from the quake's epicenter to feel that). Also, "an approaching tsunami will drain the coastline as water rushes out," he says.

People in its path can hear a tsunami's approach, he says: it sounds as loud as a jet plane or a locomotive. When they see the rushing water or hear the approaching tsunami, he says, they have about five minutes to flee to higher ground.

Write to Sharon Begley at sharon.begley at wsj.com10 and Gautam Naik at gautam.naik at wsj.com11

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