Operators of the 800-mile trans-Alaska oil pipeline said Sunday night they probably won't know until midmorning today how long the line will remain shut down because of Sunday's earthquake.

The pipeline, vital for the state's economy, began shutting down automatically after the 7.9 quake hit. Workers with Alyeska Pipeline Service Co. took over manual control and had the entire line down by 2:12 p.m., said spokesman Mike Heatwole.

The pipe did not break and no oil spilled, he said.

But eight of the H-shaped brackets that cradle the 48-inch line above ground were damaged. At each support, a metal piece called a shoe that supports the pipe on the bracket's crossbeam fell to the ground, Heatwole said.

At five brackets, the crossbeam was damaged or dropped out, leaving the pipe hanging, he said.

The damage occurred at Mile 588 of the pipeline, about 48 miles south of Delta Junction.

Alyeska mobilized as many as 100 workers Sunday, Heatwole said. They looked for pipeline damage from the air and on the ground. Damage appeared to be isolated to the area south of Delta Junction, he said.

At first light, Alyeska planned to send out teams with experienced engineers to assess the damage, Heatwole said.

Workers will begin cribbing -- building wooden support structures to relieve stress on the pipeline.

"We don't know how long we're going to be shut down," Heatwole said Sunday night.

The pipeline, in operation for more than 25 years, crosses three fault lines, including the Denali fault that spawned Sunday's quake and runs near where the damage occurred.

The pipeline was built with many features to prevent catastrophe, including an earthquake detection system that can shut down the line automatically.

Some above-ground sections zigzag across the landscape to allow the pipeline to expand or contract, like an accordion, from earthquakes or temperature changes.

The shoes on the H support beams move, allowing the pipeline to slide back and forth and side to side.

The pipeline is rated to withstand earthquakes of magnitude 5.5 to 8.5 depending on the area. The section south of Delta Junction where the damage occurred Sunday is designed for an 8.0 quake, Heatwole said.

Shutting down the pipeline is a complex operation. Along the pipeline, valves close and pump stations stop. Oil production from North Slope wells also must slow or stop.

The pipeline is vital to the state's economy. Each day it carries more than 1 million barrels of crude oil worth more than $25 million at current prices. The state government depends heavily on oil royalties and taxes.

Alyeska is an Anchorage-based consortium that operates the pipeline for the six oil companies that own the line -- BP, Conoco Phillips, Exxon Mobil, Amerada Hess, Unocal and Williams.