One unexpected finding from the scientists’ experiments was that their laser pulses triggered not only seismic waves but also airborne waves that skimmed over the models’ top surfaces. There’s plenty more to investigate using these models, the researchers suggested. These results were presented today at AGU’s Fall Meeting 2021. “ are in some sense opposite of our conventional understanding.” That’s a surprise, said Park, because sedimentary basins have long been believed to be amplifiers of ground motion. Those waves tended to be selectively reflected back at the edges of a basin, the team showed. The researchers found that higher frequencies of ground motion in their models-corresponding to real-life frequencies above 1 hertz-were generally reduced within basins. The thermal energy of the laser pulses heated the models, resulting in differential stresses that translated into movement, albeit very small: Park and her colleagues recorded ground motion at the top of the models on the order of tenths of nanometers. The team members generated extremely tiny earthquakes in their models by bombarding them with megahertz-frequency laser light. “It has all these structures within it,” said Park. But in actuality each one captures a range of geological structures within the 50-kilometer-wide Los Angeles basin at a scale of 1:250,000. The models the researchers produced, measuring roughly 20 centimeters long by 4 centimeters wide by 1 centimeter thick, aren’t much to look at from the outside, said Park. “That’s how you can print a variable range of densities.” By changing the printing parameters-including the speed of the sintering laser and its power-it’s possible to control how much pore space remains, said Park. The researchers printed their models much in the same way that ink is printed on paper: They laid down successive layers of powdered stainless steel and then used a laser to heat and join (“sinter”) the layers together. “If it’s rigid, it has a much larger range of material properties.”
That choice was mainly dictated by steel’s rigidity, said Park. That’s roughly a factor of 10 better than the spatial resolution of a numerical model that’s commonly used to study the Los Angeles basin, said Park.Īfter experimenting with materials such as rubber and plastic, Park and her colleagues settled on stainless steel as their preferred printing medium. Park and her team realized that they could reproduce even relatively small natural variations in density-corresponding to about 10 meters in size in real life-in their 3D printed models. “We don’t want to have our model running for 20 years.” A Boost in Resolutionįor that reason, Sunyoung “Sunny” Park, a seismologist at the University of Chicago, and her colleagues recently began 3D printing models of the Los Angeles basin. Nweke, a civil engineer who works on natural hazards at the University of Southern California in Los Angeles who was not involved in the research.īut reproducing the small-scale details of a sedimentary basin in a numerical model is challenging, said Nweke, given inherent trade-offs between a model’s spatial resolution and the computational time required to run it. “Imagine a bowl being filled up with stuff,” said Chukwuebuka C. They start out as depressions that over time become filled in with lower-density material deposited by rivers and landslides. Sedimentary basins are complex geological structures.
“We don’t want to have our model running for 20 years.” Get the most fascinating science news stories of the week in your inbox every Friday. That’s wholly unpredicted by numerical models, the team noted.
They found that the highest-frequency seismic waves-those that generate sudden changes in acceleration and are therefore the most destructive to buildings-were actually attenuated within the models’ basin.
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Now, to more thoroughly study how seismic waves travel through a sedimentary basin, researchers have conducted a series of seismic experiments using 3D printed models of the underbelly of Los Angeles. Add in the fact that these cities are prone to earthquakes, and that’s potentially a recipe for disaster: Numerical modeling has suggested that ground shaking is amplified within basins.īut such modeling-an oft-used resource for understanding ground motion in sedimentary basins-is often limited in its spatial resolution and is furthermore constrained by the equations it receives as input. Some of the world’s largest cities-including Los Angeles, Mexico City, and Santiago-are located in naturally occurring sedimentary basins.
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