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A small earthquake could pose a big risk to a US city

Aerial view of Salt Lake City, Utah

Aerial view of Salt Lake City, Utah

Downtown Salt Lake City, Utah, could sustain serious damage in a relatively small earthquake. Credit: Aerial Archives/Alamy

Seismology

11 June 2021

The structure of faults beneath Salt Lake City, Utah, shows how the ground could liquefy during a shaking.

Geologists have long known that Salt Lake City, home to 200,000 people, lies atop a network of geological faults. Now, research shows that, during an earthquake, these faults could cause the ground beneath downtown buildings to flow like liquid.

The city, which is Utah’s capital, lies between two large mountain ranges created by geological activity. Active faults snake near those mountains, along them and beneath Salt Lake City. But it has been unclear precisely how the faults linked underneath the city, and how much damage they might cause during a large earthquake.

Lee Liberty at Boise State University in Idaho and his colleagues probed the buried faults by repeatedly dropping a 200-kilogram weight along the city’s streets. The scientists then analysed how seismic energy from the impact rippled through the ground.

They found that faults shoot through many rock layers that lie beneath the city. Even a relatively small earthquake, with a magnitude of less than 5, could cause the ground to liquefy in these areas. A 6.5-magnitude earthquake could damage buildings substantially.

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