On Sept. 19, 1985, an earthquake struck Mexico City — and it was a big one, rating at 8.1 magnitude.
Despite the epicenter being 250 miles west from the city, the National Institute of Standards and Technology (NIST) said the quake shook the relatively unstable ground for nearly three minutes. "As the aquifer under the city has slowly drained, it has been discovered that the city sits atop a combination of dirt and sand that is much less stable than bedrock and can be quite volatile during an earthquake," NIST said in a report.
The death toll was unthinkable — 10,000 perished. Some 30,000 were injured. An estimated 250,000 were left homeless. Nearly 3,000 buildings were completely demolished. And another 100,000 had serious damage.
Worsening the blow, just over a day later, a 7.5-magnitude aftershock hit.
In the aftermath, scientists looked at what could be done to prevent such a tragedy of this magnitude from happening again. By 1990, an early warning system, called SASMEX was in place to give immediate warning to those in harm's way. This was combined with efforts to reinforce the city's structures and establish strict building codes for new structures to protect against future quakes, according to the Christian Science Monitor.
All of this is extremely relevant to the United States and, in particular, California. With depleting groundwater, a side effect has been a rise in the Earth's surface, which may end up triggering small earthquakes, according to the National Science Foundation. And we're due for another big quake soon, as previous major quakes in the region have happened every 110 to 140 years. Los Angeles isn't out of the woods, according to the Smithsonian Magazine. The last big quake to hit that region was 1857, with the 7.9-magnitude Fort Tejon quake, 158 years ago. And we're sitting at 147 years since the 1868 temblor on the Hayward Fault in the San Francisco area, while the northern part of the San Andreas fault last hit San Francisco in 1906 — 109 years ago — which has been compared in the tragedy's magnitude to Hurricane Katrina.
(Photo at top: Mexico City's General Hospital collapsed in the quake. Source: United States Geological Survey)