Lasers and 3D printing reveal how the ground shakes after earthquakes

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On a sunny September morning in 1985, a massive earthquake killed more than 9,000 people in Mexico City, even though the quake’s epicenter was about 200 miles away.

The worst damage occurred in the city itself, in part because Mexico City is built on an ancient basin surrounded by mountains. The soft foundation is thought to have amplified the shaking, causing seismic waves to ricochet through the ground.

Scientists are concerned because many populated cities around the world, such as Los Angeles, are built on similar basins, and it has been difficult for researchers to understand how the ground moves during such earthquakes. But an innovative technique using 3D printing and lasers could help improve our knowledge of what happens during ground shaking and how different formations and layers beneath the ground mitigate or increase earthquake damage. earth.

“We know you would feel the same earthquake differently if you were in a basin or on a mountain, but predicting or simulating that is really hard, in part because it’s just hard to get the level of detail that you need,” Sunyoung Park said. , a geophysicist at the University of Chicago and lead author of a study describing the process published in Scientific reports. “With these 3D models, you can get a level of granularity that really helps you see patterns that you wouldn’t see otherwise. It’s a really great technique.

Ground Truth

Under our feet, the ground is composed of different layers deposited for eons. These can range from soft clay to brittle shale. Everyone reacts differently to an earthquake – for example, more flexible layers can absorb some movement, while others amplify it. The depth and intensity of an earthquake as well as the surrounding geography can also play a role, causing waves to ricochet. All of these factors combine to make predicting earthquake damage extremely difficult.

Scientists can use computers to try to model what’s going on, but that’s imperfect. “Simulating all of this is really hard to do, not only because it’s computationally intensive, but we don’t know enough about the physics on a small scale, that is, up to a mile in diameter or less,” Park explained. “For example, if there are water-filled aquifers or magma chambers, how does that affect the waves? We don’t really know.

Since the 1920s in Japan, scientists have experimented with building real physical models of the ground to understand what happens during earthquakes. But they are extremely laborious and limited. “You have to cut out a lot of individual layers and try to glue them perfectly together, and there are so many different types of rock that it’s hard to get accurate replicas,” Park said.

Park and his collaborators therefore thought that it would be a perfect application for 3D printing.

With a special metal 3D printer, they could create as many layers as they wanted, perfectly nested on top of each other. It starts with metal powder, which is heated by a laser to form one layer at a time; by varying the intensity and scanning speed of the laser, they can make each layer more porous or denser, to simulate different types of rock.

Using this method, the scientists created an exact replica (at a scale of 250,000 to 1) of the rock beneath the city of Los Angeles, which was just eight inches long.

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