Tuesday, January 6, 2009

'Very bad' tornado season has most deaths since 1968

'Very bad' tornado season has most deaths since 1968

Iowa's 2008 tornado season took 12 lives, injured at least 130 people and matched 2001 for the second-most twisters in a year at 105.

Pack those statistics into the four-month period of April through August and one word comes to mind: devastation. That was the same term many used to describe the EF5 storm that tore through Parkersburg and the EF3 tornado that struck the Little Sioux Boy Scout camp.

The Parkersburg twister accounted for eight fatalities when it spun a 43-mile path through Grundy, Butler and Black Hawk counties on May 25, and the storm that touched down near Little Sioux on June 11 killed four, including Boy Scout Aaron Eilerts, 14, of Eagle Grove.

"This is total devastation," said Sarah Harberts, 28, after Parkersburg was hit by the first EF5 tornado in Iowa since 1976. Harberts, who lives in Atlanta, was in Parkersburg visiting family on the day of the storm. Together, according to statistics from the National Weather Service, the pair of storms accounted for all 12 fatalities and more than $100 million in damages to homes, businesses and infrastructure.

"All of the buildings are gone; most of the tents are gone; most of the trees are destroyed," Lloyd Roitstein, president of the Boy Scouts' Mid-America Council, said days after a tornado ravaged the Boy Scout camp. "You've got 1,800 acres of property that are destroyed right now."

According to a year-end statement from state climatologist Harry Hillaker, 98 of 99 counties in Iowa, with the exception of Audubon County, reported tornadoes in June.

The deadly 2008 twister season in Iowa was "very bad" overall, National Weather Service meteorologist Jeff Johnson said, but especially when compared to past numbers.

According to state records, the dozen deaths in 2008 are the highest total since 1968. The National Weather Service began keeping official records in 1950.

"It was a very bad year, we had a lot of problems with tornadoes," Johnson said. Although the numbers were not favorable, advances in technology and science, he added, will help state weather experts work together with spotters from across the state in ensuring additional safety during tornado season.

"Probably the biggest advancement for us has been the Doppler radar, which isn't new technology," Johnson said, adding that robust spotter training has helped advance the ability to warn Iowans of possible storms. "It's really an integrated process - what we're doing here at the National Weather Service while working with spotters to mutually help each other, the end result has helped tornado safety overall."


Great Indian Ocean earthquake of 2004 set off tremors in San Andreas

In the last few years there has been a growing number of documented cases in which large earthquakes set off unfelt tremors in earthquake faults hundreds, sometimes even thousands, of miles away.

New research shows that the great Indian Ocean earthquake that struck off the Indonesian island of Sumatra on the day after Christmas in 2004 set off such tremors nearly 9,000 miles away in the San Andreas fault at Parkfield, Calif.

"We found that an earthquake that happened halfway around the world could trigger a seismic signal in the San Andreas fault. It is a low-stress event and a new kind of seismic phenomenon," said Abhijit Ghosh, a University of Washington doctoral student in Earth and space sciences.

"Previous research has shown that this phenomenon, called non-volcanic tremor, was produced in the San Andreas fault in 2002 by the Denali earthquake in Alaska, but seeing this new evidence of tremor triggered by an event as distant as the Sumatra earthquake is really exciting," he said.

Ghosh is to present the findings next week (Dec. 17) in a poster at the American Geophysical Union annual meeting in San Francisco.

The Indian Ocean earthquake on Dec. 26, 2004, was measured at magnitude 9.2 and generated tsunami waves that killed a quarter-million people. It was not known, however, that an earthquake of even that magnitude could set off non-volcanic tremor so far away.

The San Andreas fault in the Parkfield region is one of the most studied seismic areas in the world. It experiences an earthquake of magnitude 6.0 on an average of every 22 years, so a variety of instruments have been deployed to record the seismic activity.

In this case, the scientists examined data from instruments placed in holes bored in the ground as part of the High-Resolution Seismic Network operated by the University of California, Berkeley, as well as information gathered by the Northern California Seismic Network operated by the U.S. Geological Survey.

Signals corresponding with non-volcanic tremor at precisely the time that seismic waves from the Indian Ocean earthquake were passing the Parkfield area were recorded on a number of instruments as far as 125 miles apart.

"It's fairly obvious. There's no question of this tremor being triggered by the seismic waves from Sumatra," Ghosh said.

Scientists have pondered whether non-volcanic tremor is related to actual slippage within an earthquake fault or is caused by the flow of fluids below the Earth's surface. Recent research supports the idea that tremor is caused by fault slippage.

"If the fault is slipping from tremor in one place, it means stress is building up elsewhere on the fault, and that could bring the other area a little closer to a big earthquake," Ghosh said.

Monitoring tremor could help to estimate how much stress has built up within a particular fault.

"If the fault is closer to failure, then even a small amount of added stress likely can produce tremor," he said. "If the fault is already at low stress, then even high-energy waves probably won't produce tremor."

The work adds to the understanding of non-volcanic tremor and what role it might play in releasing or shifting stress within an earthquake-producing fault.

"Our single-biggest finding is that very small stress can trigger tremor," Ghosh said. "Finding tremor can help to track evolution of stress in the fault over space and time, and therefore could have significant implications in seismic hazard analysis."


Busy night for air-sea rescues

A fisherman whose boat sank after hitting a buoy in the Solent was plucked to safety last night by a passing rescue helicopter.

The man, in his 20s, was taken to hospital with shock and hypothermia after being winched to safety from the Solent. He sent out a mayday at 2344 yesterday when his boat, Sea Raider, started sinking as he returned home to the Isle of Wight.

He was rescued by helicopter, diverted en route to a medical evacuation in Jersey.

A spokesman said: "He was pretty lucky that the helicopter was in the air at the time otherwise he would have been in the water a lot longer. It's not so much the water temperature, which is about 7C, but the air temperature is pretty cold. Shock is a bigger killer than the water."

Meanwhile, a Burmese sailor was seriously injured in a 40ft fall on board a cargo ship, 600 miles off the west coast of Ireland last night. He was airlifted to safety in an operation masterminded by RAF Kinross and involving two US Army long-range helicopters, a Hercules aircraft and an aircraft tanker from the US airbase at Lakenheath in Suffolk.

A RAF Nimrod provided air cover and communications. The crewman man suffered spinal and cranial injuries.


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