November 28, 2002	Thursday	Ramazan 22, 1423

ANCHORAGE: While it did little serious damage, the magnitude-7.9 earthquake that rattled interior Alaska earlier this month revealed a bounty of scientific information for seismologists and geologists.

They discovered deep cracks in glaciers that mirror the fault at the quake’s source and a previously undetected neighbouring fault, and they gained a better understanding of earth movements and earthquake ripple effects.

The November 3 earthquake started as a vertical thrusting motion south of Fairbanks, then transformed into a horizontal shaking motion along the well-known Denali fault, releasing most of its seismic energy on the eastern end, scientists said.

A quake of 7.9 magnitude is capable of causing tremendous, widespread damage in populated areas. In that thinly populated part of Alaska the earth shifted as much as 22 feet (6.7 metres), leaving chasms in roads, knocking buildings off their foundations and tipping over heavy fuel tanks.

“If this would have happened in California, it would have been just disastrous,” said Alaska state seismologist Roger Hansen.

The initial shaking led to the discovery of a previously unknown thrust fault, a feature that moves vertically.

“The discovery of the thrust fault was completely a surprise,” said Peter Haeussler, a U.S. Geological Survey scientist helping lead the post-quake studies. “Before that, it was completely unknown. People didn’t know that fault existed.”

QUAKE BENEATH GLACIER

The earthquake was the first recorded since 1958 that had run beneath a glacier, Haeussler said. Aerial surveys afterwards revealed deep cracks that followed the Denali fault’s route.

“It’s almost like a huge mole track,” Haeussler said.

Until now, scientists had not known exactly where the fault ran beneath the glaciers. The cracks and marks on the ice surface solved that mystery, he said: “There it is. There’s the location.”

Details about the earthquake were gleaned with the help of instruments already in place, some of them put there after a magnitude-6.7 quake that occurred in the same area two weeks earlier.

Some of the findings are documented in a so-called “ShakeMap” issued by the USGS. The map, the first of its kind, identifies the areas of most violent shaking and is meant to help emergency managers plan for future events.

The Denali fault has been studied for years, but until recently some scientists were unsure whether it was capable of producing a major quake. Not so after November 3, said Hansen.

“I think that laid that to rest,” he said.

The Denali fault, a so-called “strike-slip” system located entirely on land, is similar to California’s famous San Andreas fault. But the effects of the earthquake were far different from what they would have been farther south.

“This type of quake would be the, quote, Big One, unquote, that they are all expecting on the San Andreas fault,” Haeussler said.

ONLY ONE INJURY: Alaska’s most destructive earthquake hit magnitude 9.2 in 1964 and killed 131 people. That earthquake was centred offshore in Prince William Sound and produced by a different type of fault, one that separates oceanic and continental rocks. It was the second most powerful earthquake in recorded history.

The November 3 quake, though one of the most powerful recorded on U.S. soil, produced only one serious injury, a broken arm suffered by an elderly woman who slipped while fleeing her home.

Much of the property damage occurred to roads and bridges, where the toll is at least $25 million, according to state estimates. Some affected villages have had drinking water problems.

The trans-Alaska oil pipeline shut down after pieces of some vertical supports fell off, but the line itself was unscathed and oil flow resumed three days after the earthquake.

Fairbanks, Alaska’s second-biggest city, was spared the brunt of the earthquake, even though it was only 93 miles north of the epicentre. That was thanks to the eastward trend of the seismic energy.

At the time the quake struck, Hansen, a Fairbanks resident, thought it was merely an aftershock of the October 23 tremor.

Coffee sloshed from a cup on his table, and a picture fell of a bookcase, but the quake did not seem that powerful to him, he said. “I didn’t think much of it until I realised it didn’t quit,” he added.—Reuters