Engineering and the Mexico City Earthquake
Phillip Keane posted on September 30, 2017 |

It’s been a bad month for Mexico, having endured three earthquakes in September alone. The worst of these quakes struck the densely populated capital Mexico City on the Sept. 19, measuring in at a magnitude of MW 7.1 and resulting in 344 deaths and over 6,000 injuries. The casualties are still being counted as of this morning, 10 days after the event, although it is being reported that the final damaged buildings have been declared clear today. The long process of rebuilding property and lives can now begin.

Hotel in Mexico City wrecked by earthquake this month. (Image courtesy of Angel Hernandez/EPA.)
Hotel in Mexico City wrecked by earthquake this month. (Image courtesy of Angel Hernandez/EPA.)
It should be pointed out that this month’s Mexico City earthquake occurred (coincidentally) exactly 32 years after the 1985 Mexico City earthquake, which itself resulted in over 10,000 fatalities. On the morning of Sept.19, a memorial service for the 1985 earthquake was held, and national earthquake drills were conducted up and down the country. Then two hours after the drills were performed, at 1pm local time, the earthquake hit.

Mexico is a seismic hotspot, largely thanks to it sitting at the junction of three tectonic plates. And Mexico City suffers from amplified earthquake effects due to being built on top of an ancient lake bed. The sediment layers on the lake bed can amplify the effects of a quake. “When earthquake waves pass through it, it jiggles, magnifying the vibrations,” John Bellini, a geophysicist with the U.S. Geological Survey, told The Verge. “So the reason that Mexico City seems susceptible to more damage is because of this amplification effect of the lake bed.”

Since the 1985 earthquake, new building rules and emergency procedures have been implemented to reduce the destruction caused by these more powerful earthquakes in Mexico City. For the most part, the rules appear to be working: Most of the buildings that sustained heavy damage this month were those that were built prior to 1985 and were therefore not subjected to the new rules. In addition, many properties destroyed were built after 1985, but by unscrupulous construction companies who try to save money by using thinner mixed cement, or thin walls (in contradiction to the rules).

Although these rules were relatively quick to draft, implementing them into building codes and seeing wide adoption can potentially take decades. And this lag in adoption by the construction industry shows the disconnect between the state of the art at the time, and the state of the art by the time these rules are implemented. The pre-1985 buildings collapsed recently because they were constructed according to knowledge at the time. The post-1985 rules were based on the lessons learned in the 1985 quake. And now, 32 years later, everyone is talking about how the current state of the art could have helped Mexico City…and how long it will take to implement.

For the first part, the research horizon for earthquake detection and damage reduction is looking pretty good. Much of what determines whether a structure will survive or not is down to the ductility and strength of the materials. Flexible materials will dissipate forces better that brittle ones. Engineers are currently researching use of laminated wood building frames due to the flexibility of the engineered wood. In addition, there is research into using polymers and foams in between building joints, to allow the building to flex and dissipate stress under force.

Shape memory alloys, self-healing materials, variable-stiffness meta-materials, big data, satellite remote viewing and early warning systems connected to infrastructure grids that shut down to prevent damage during an event…all of these things are either being researched or developed as we speak. From a research standpoint, there are reasons to be optimistic. However, as mentioned, the industry takes time to respond, and bureaucracy takes even longer.

“I’m confident that we do know how to build structures that can go through the most severe earthquake shaking, but we’re not currently doing that,” said Thomas Heaton, professor of geophysics and engineering at Cal Tech, in an interview with Futurism.com. “People are too busy making money to really invest in what’s necessary based on things that we’ve learned over the last 20 to 30 years.”

All Mexico City can do is stay prepared, and wait. The good news is that there is useful technology just around the corner. They’re just not sure when exactly it will arrive.

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