A CONVENTION centre鈥檚 extension, built for the Winter Olympics in Salt Lake City earlier this year, straddles an active earthquake fault line according to geologists in Utah. They say their warnings weren鈥檛 heeded when the extension was built and that if a quake does strike, the building could be torn in two.
Roy Shlemon was called to the Salt Palace construction site to give a second opinion in 1999, after local geologist David Simon found what looked like a fault line. By digging trenches and examining the soil layers, they found that the ground had fallen by 1.5 metres between 7000 and 8000 years ago, and that there had been several more recent, smaller shifts. 鈥淭here鈥檚 no doubt in my mind that this is an active fault,鈥� says Simon.
In Utah, as in many places around the world, it鈥檚 illegal to build across a fault known to have been active in the past 10,000 years. While most of the damage during a quake is caused when the ground shakes, buildings stand no chance if the ground beneath part of the foundation drops by say a metre. But relocating Salt Palace would have cost millions of dollars, so the county planning authority sought further opinions.
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Consultant Les Youd said he believed the slip might have been caused not by a quake but by soil liquefaction, brought on by a tremor in a known fault line nearby. Movements in a layer of silt about 30 metres down could have forced slabs of land to slip sideways downhill, he says, creating the appearance of a vertical shift in the soil. Because the water table has dropped since then, a future quake wouldn鈥檛 cause the same problems.
In 2000, an independent consultancy firm based in California concluded that there wasn鈥檛 enough evidence of faulting, so the building was completed, with steps taken to strengthen the foundations.
In Youd鈥檚 opinion, it was the right decision. But Shlemon and Simon disagree. Simon points out that the slip is linear and unbroken, it lines up with a known fault that is six blocks further north, and branches into multiple cracks near the surface 鈥� all evidence more consistent with faulting than sideways spreading. 鈥淭he lateral spread hypothesis just isn鈥檛 physically possible,鈥� says Simon. Shlemon will present their views at an environmental catastrophes meeting in London this week.
The two geologists are concerned that financial pressures might have been a factor when Salt Palace was given the go-ahead. 鈥淚f you get enough [scientific] opinions, eventually you鈥檒l get the one you need,鈥� says Simon. He and Shlemon argue it would have been better to play safe. 鈥淚f you have a plane and there鈥檚 a 50:50 chance the wing will come off, you don鈥檛 fly,鈥� says Shlemon.
Youd agrees that further studies should be done to find out where the fault line just to the north actually stops. 鈥淲e still don鈥檛 know where it goes. Finding these faults should be a high priority,鈥� he says.
But there are no plans to do that, says Gary Christenson from the Utah Geological Survey. An imaging technique called seismic reflection profiling could be used, but it鈥檚 expensive. And if a fault were found, demolishing buildings would be very unpopular, Christenson points out. 鈥淭hat would be impossible here.鈥�