Metal 3D Printed Model Offers Insight into Earthquakes’ Seismic Waves

It seems like no matter where you live, there is some sort of extreme weather situation to deal with; I’m in Ohio, so we have tornadoes all spring. In more tropical climes, like Australia, India, and North America’s Gulf Coast, there are hurricanes, and blizzards are fairly common in the upper Midwest and the Great Plains, though they can also strike high altitude mountaintops in the tropics.

Out west, and in places like Nepal and Haiti, there are earthquakes, which have always seemed really scary to me; more than 9,000 people were killed in a huge earthquake in Mexico City in 1985, even though its epicenter was over 200 miles away. But researchers at the University of Chicago are using 3D printing to learn more about how the ground shakes after an earthquake, and how the layers underground can either increase or decrease the damage.

University of Chicago geoscientist Sunyoung Park shows seismic wave simulations from a new technique that uses metal 3D printers to better understand earthquake shaking.

Different layers, built up over billions of years, make up the ground, and they’re all different—some may be brittle, others soft. During an earthquake, these layers all react differently, and seismic waves can ricochet depending on how intense and deep the quake is, in addition to nearby geography. So it’s very tricky to predict the damage an earthquake might cause. For instance, Mexico City is built on an ancient basin that’s surrounded by mountains, and researchers believe that the area’s soft foundation caused the shaking to be stronger, which led to terrible damage. Computer models help a little, but they’re not perfectly accurate.

“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 at small scales—that is, down to the level of a mile across or less. For example, if there are aquifers filled with water or magma chambers, how do those affect waves? We don’t know very well,” said Sunyoung Park, a geophysicist with the University of Chicago.

Physical models of the ground have also been tried, but they take a long time to make, and the scope and range is limited at best. But 3D printing might be a better approach for modeling an earthquake. Park and the other researchers published a paper on their work, describing how they used a Concept Laser M2 Cusing metal 3D printer, and its direct metal laser melting (DMLM) technology, to gain a better understanding of how seismic waves move through the ground. The printer’s laser heats stainless steel powder to form multiple layers on top of each other, and by changing up the speed and intensity of the laser, it can actually simulate different rock types by making the layers more dense or porous.

“We know that you would experience the same earthquake differently if you were in a basin or on a mountain, but predicting or simulating that is really difficult, in part because it’s just hard to get the level of detail you need. With these 3D models you can get a level of granularity that really helps you see patterns that you wouldn’t otherwise. It’s a really neat technique,” explained Park, who was the lead author of the study.

Park, center, works with members of her group Sifang Chen, left, and Jiong Wang, right.

The team wanted to study how seismic waves with differing frequencies spread through the ground, and specifically focused on high-frequency waves, as they’re believed to be responsible for more building and infrastructure damage. Using the printer, they 3D printed an 8 inch-long replica, at a 250,000 to 1 scale, of the rock underneath Los Angeles, which is not dissimilar to the rock under Mexico City. Using lasers and other equipment, the researchers simulated an earthquake, and monitored the 3D printed model to see how the waves moved through the layers.

According to Park, the results were very similar to data recorded during actual earthquakes, but they were surprised by some findings, such as the fact that “the high-frequency waves are more diminished” within the basin, “which is almost exactly the opposite of what was previously thought.” Because other scientists observed that low-frequency waves were amplified within a basin environment, they figured it would be the same way for high-frequency waves. But using the metal 3D printed model, the UChicago team discovered that high-frequency waves seem to reflect off at the edge of the basin.

Park explained, “It seems to imply that what we have been understanding for low-frequency waves does not hold up for the higher-frequency waves, and that we may need a different framework to understand these shakes.”

Setup for the seismic experiments on the 3D printed model. Thin arrows show the locations of the laser source (red) and receiver (blue). Thick red arrow shows the direction at which the laser is scanned along the top side of the model.

In addition to the fact that it only takes a few hours to print one of these models, they can also be reused; Park said that the team has used its Los Angeles replica in over 2,000 experiments. Plus, she believes that these models could be used for similar types of research as well.

“We could even do other planets; for example, we know from seismic sensors on the moon and Mars that they experience Marsquakes and moonquakes, but their recordings look quite different from those of earthquakes. You could imagine creating scale models of the moon or Mars to try to understand,” she concluded.

Park holds a prototype model, which is made in translucent material to show the layers. The metal block to the left is a completed model representing the ground below Los Angeles.

(Source: University of Chicago / Photos by Jason Smith)