What Makes a Tsunami?
Experts urge to have emergency plan
January 31, 2005 3:45 PM
Around the rim of the Pacific Ocean, from California to the island nations of Southeast Asia, lies a region known by geologists as the Ring of Fire.
Within this circle of seismically active terrain, volcanoes sprout like wheat while earthquakes rumble with ominous intent along fault lines defined by massive, continental-sized plates. It is a dangerous part of the world, a tectonic time bomb just waiting to happen.
In December, the inevitable finally did happen as a magnitude 9.0 earthquake struck off the island of Sumatra in the Indian Ocean. In a span of 3 to 4 minutes, the quake released as much energy as 475 million tons of TNT along a fault line over 1,000 miles long and nearly 100 miles wide, according to the U.S. Geological Service.
Scientists estimate the seabed dropped 65 feet, creating a wall of water as tall as a four-story building. The massive wave then spread outward at the speed of a jetliner, killing more than 150,000 people in coastal nations all around the Indian Ocean and leaving millions more in its wake coping with one of the worst natural disasters in human history.
San Francisco lies on the eastern edge of the Ring of Fire, surrounded on three sides by water. So could a tsunami like the one in the Indian Ocean affect people here, in earthquake-prone California?
“Any ocean, any coast is subject to tsunamis,” said Bruce Turner, one member of a team of oceanographers and other experts who monitor the coast of the Western United States at the West Coast and Alaska Tsunami Warning Center in Palmer, Alaska.
Using data gathered from seismometers scattered across the globe, Turner and his colleagues watch for the next big earthquake that might generate a tsunami. Since the warning center does not have funding for round-the-clock operations, Turner carries a pager hooked up to an Internet-connected computer that signals an alert when a major earthquake occurs near the Pacific Ocean.
Turner and the rest of the staff at the warning center must live within five minutes of the office, just in case they need to issue urgent warnings about a destructive wave headed for American shores.
Tsunamis have struck the United States several times over the past century, Turner said, including a wave that struck near the Bay Area in 1991, but caused no reported damage. The warning center was created after a magnitude 9 quake struck Alaska’s Prince William Sound, generating a tsunami that killed 157 people along the West Coast, he added.
Although the United States maintains a series of six tsunami detection buoys spread around the Pacific Ocean that directly measure tsunami waves, only three of the buoys are currently functional due to maintenance problems and the corrosive saltwater environment. Because of the difficulty in maintaining the buoys, Turner and other scientists rely on indirect methods of spotting killer waves.
“We’re very seismically oriented,” Turner said. “We have about 150 (data) channels coming in to us, most by Internet but some by private channels. We really don’t do a lot until the earthquake gets to a (magnitude) 6.5. At a 7.1, we send out a warning. The next few hours are a watch situation. We don’t take any chances.”
Oswaldo Garcia, chair of the Geosciences department at SF State, agrees that it’s best not to take risks when dealing with tsunamis, as they occur more often than many people may realize.
“Tsunamis are generated fairly frequently, mostly in the Pacific Basin,” Garcia said. “There’s an area west of Sumatra that’s very active.”
But Garcia said that danger of tsunamis is not solely dependant on the magnitude of an earthquake. The specific geology in an earthquake zone also plays an important role.
“There are different types of earthquakes. In our area, the type of interaction is a sidewise motion. You see a motion to the left here. The earthquakes that generate the tsunamis are the ones where you have subduction zones,” said Garcia.
Subduction zones are areas where, according to one widely held theory known as plate tectonics, parts of the Earth’s crust run into and over each other, causing one side to rise and the other to sink, sometimes violently and usually without warning.
“Chile and Alaska are two places where that happens pretty frequently,” said Garcia.
Garcia also pointed out that SF State students have an excellent opportunity to learn more about what causes earthquakes, volcanoes and tsunamis. The Geosciences department currently offers a 9-unit block of courses collectively called ‘Our Violent Planet,’ which is designed to give students insight into many of the natural forces that shape our world. Taking the courses counts towards general education credit and fulfills SF State’s Segment III graduation requirement.
“They’re popular classes,” said Garcia.
In Sacramento, Eric Lamoureux, a spokesperson for the Governor’s Office of Emergency Services, said that his office is prepared for a tsunami should one strike here.
“Our most significant risk for tsunamis is in Northern California,” said Lamoureux. “We’re certainly prepared to respond to all kinds of emergencies in this state.”
Still, Lamoureux cautions that the danger to California from a tsunami is relatively low. He said his office is spending much more time recently dealing with fires and floods, which are far more common in the state than either earthquakes or tsunamis.
“The important thing to note is that the probability of having devastation on the same scale as we saw in Asia is not going to happen here,” said Lamoureux.
While Lamoureux said emergency workers are ready to respond in the event of a large-scale natural disaster, he urges self-sufficiency.
“Know where your evacuation routes are in the event of an emergency,” Lamoureux said. “Having an emergency supply kit that is going to make you self-sufficient for at least a three-day period of time is really important. Be aware, be informed and don’t rely solely on the government to step in and take care of all your needs following a natural disaster.”
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