Is your building safe after an earthquake? These cheap sensors could tell you
By Lizzie Wade
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In recent years, small accelerometers—devices that precisely measure movement in 3D space over time—have gotten better and cheaper. Used in smartphones, cars, and video game controllers, the accelerometers are now sensitive enough to detect faraway tremors and subtle building vibrations.
Researchers at Grillo say installing Pulse sensors on each floor of a building lets them measure a crucial indicator of structural health, a ratio called interstory drift—how much floors suddenly jerk out of alignment during a quake. "Buildings can withstand some interstory drift," says Monica Kohler, a civil engineer and seismologist at Caltech. But beyond a certain threshold that varies by building, they become permanently damaged and can even collapse, she says. To determine damage, these systems compare a building's interstory drift to limits determined by computer models—ideally crafted from structural drawings for that particular building.
That's not realistic for individual homes or schools in a developing country such as Mexico. Instead, Grillo uses standard blueprints for various building types. The concrete-frame, two-story elementary school here, for example, is "as typical as you're going to get in Mexico," says Andrés Meira, an architect and the founder and CEO of Grillo. "Unless there's some trickiness in how they constructed it, we should have a pretty good idea of how it should move." Grillo has declined to install Pulse in buildings that don't follow standard designs.
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Pulse doesn't replace those expert inspections, but should serve as a tool that experts can use to prioritize their work in the chaotic hours and days after a strong quake, [Luis Rodríguez Abreu, a seismologist at Grillo,] says. It can also warn people of hidden damage, which can be deadly. For example, 50 minutes after the shaking stopped in Mexico's 2017 earthquake, a four-story office building in Mexico City collapsed—after some people had returned to work inside.
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