Anchorage earthquake put new mapping tool to the test

A new USGS tool modeled potential liquefaction sites after the Nov. 30 Anchorage earthquake (Courtesy of U.S. Geological Survey).

The 7.0 Anchorage earthquake last month caused several landslides and other dramatic ground movements. It was one of the first big tests of a new computer model aimed at quickly estimating how significant those ground failures will be following an earthquake.

The model is from the United States Geological Survey (USGS). After a big earthquake, it generates a map almost instantly indicating where major landslides and ground sinking or shifting are likely to take place. It also estimates how many people may be affected.

Kate Allstadt is a researcher with USGS in Colorado and helped develop the model. She says it’s intended to help first responders understand where the hardest hit areas may be in the minutes and hours after an earthquake.

“It can help decision makers figure out what areas should be a priority,” she said. “[And] if roads are blocked, which is often something that happens by landslides triggered by earthquakes, what areas might be cut off.”

Researchers have been testing the model for a few years and the public version was released in August. Allstadt says the Nov. 30 earthquake was the first chance for scientists to see for themselves on the ground how well the maps worked after a major event.

For the Anchorage earthquake, the model estimated significant landslides and other ground failures would affect about 4,400 people.

Allstadt was in Anchorage for a week of field research in early December to see if the model got it right.

“A lot of the work we did when we were in the field is taking the maps produced by these models and going to the places where they predicted higher probability of landslides and liquefaction and seeing what actually happened,” she said.

Allstadt says overall, the maps were pretty accurate. But she says they tended to overestimate where soil sinking and liquefaction might occur. And, she says, the maps are missing some important details: while they may accurately predict a large landslide that blocks a major road, they could miss a smaller slide that impacts just one house.

“Something that we’ve already been planning to do is to go to higher resolution to capture the areas that are maybe not going to produce dramatic rock avalanches, but they can be really impactful, because they’re often closer to where people live,” she said.

The model generates ground failure maps for any earthquake greater than magnitude 5.0 in the U.S and 6.0 around the world.

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