Mexico City's metro system is sinking rapidly. could be yours next

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Solano-Rojas and his colleagues found the cave-in in the area of ​​an overpass near the Olivos station, which collapsed in 2021 when a metro train was traveling on it. “We did part of this analysis before 2021 and we found that there was disparate displacement happening in that area,” Solano-Rojas says. “We were like, 'Oh, yeah, this looks like something could happen here in the future.' We think it's not a coincidence that we found it.'' Solano-Rojas was careful to say that the possible contribution of landslides to the disaster would require further assessment, and cited construction errors in the official investigation. and landslides have not been mentioned.

For this study, researchers looked at underground subway infrastructure, not subway sections — basically, the parts of the system they could verify visually. (The photo below shows the spacing of the columns supporting an overpass.) But by providing the system's operators with information about how quickly its infrastructure can degrade, their work can hopefully inform interventions. For example, engineers may add material beneath a railway to restore lost height. However, strengthening subways may be more challenging. “We don't have a concrete solution to this,” says Shirazei. “In most cases, when that happens, it results in the project being shut down and a new lane being tried to open.”

The photo shows a train crossing the bridge

Courtesy of Dario Solano-Rojas

This is not just a problem in Mexico City. Earlier this year, Shirzaei and his colleagues found that the East Coast's infrastructure is in serious trouble due to slow – but steady – deterioration. They calculated that 29,000 square miles of the Atlantic coast would sink by 0.08 inches per year, affecting 14 million people and 6 million properties. About 1,400 square miles are sinking by 0.20 inches per year.

The researchers found that individual subsidence not only threatens railways, but also all kinds of other critical infrastructure, such as embankments and airports. In a metropolis like New York City there is the additional problem of heavy weight being pushed onto the ground, which alone causes pressure on the ground. The Gulf region is also sinking. On both coasts, subsidence is greatly exacerbating the problem of sea level rise: as the water is rising, the land is sinking.

Wherever this is happening in the world, people need to stop over-exploitation of groundwater to slow down landslides. Newer-style systems are already relieving pressure on aquifers. For example, recycling toilet water into drinking water is becoming cheaper and cheaper. And more cities are deploying “sponge” infrastructure — lots of green space that allow rainwater to soak into the underlying aquifer, essentially re-inflating the land to prevent subsidence. Such efforts have become increasingly urgent as climate change has increased drought in many parts of the world, including Mexico City, putting further pressure on groundwater supplies.

With increasing satellite data, cities can get a better handle on landslides that they cannot immediately avoid. “I really feel like there is an opportunity for governments to use these types of studies to create more structured action plans,” Solano-Rojas says.