USGS says Yellowstone earthquake hazard greater than previously thought

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JACKSON, Wyo. — A new U.S. Geological Survey report indicates a slightly greater earthquake hazard in the Greater Yellowstone region of Wyoming, Montana and Idaho than previously thought, a geophysicist says.

“The new maps show how Yellowstone has had a relative increase in the hazard,” University of Utah geophysicist Bob Smith said. “It’s not a lot — it’s like 5 to 10 percent of peak acceleration.”

The USGS map of seismic hazards also shows that the region is as seismically hazardous as anywhere in the United States.

“It’s an area of well-above-normal earthquake hazard,” Smith said. “And now with all the population going in — all the new roads and dams — also high risk.”

A seasonal Moose resident, Smith was an advisory review member for the USGS report.

The nationwide USGS hazard maps and adjoining documents were last updated in 2006.

The federal document has more real-world implications than most scientific studies because it is used to determine building codes and dictates how robustly buildings must be constructed.

In a sense, the USGS seismic hazard maps are predictions of the likelihood for earthquakes.

“They are forecast maps,” Smith said, “because these are calculations of ground motions in certain time periods ahead of right now — they are essentially forms of forecastablity.”

The Teton Fault in northwest Wyoming has the highest seismic hazard in the Greater Yellowstone area, Smith said.

The last major seismic event in the Yellowstone region was the 1959 Hebgen Lake Quake in Montana.

That catastrophic quake underlines the importance of the hazard maps, Smith said.

“This is all highlighted and amplified by the fact that we had the ’59 Hebgen Lake earthquake that killed 29 people. It was a magnitude 7.3,” he said.

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