Mexico-1985

Mexico - 19th and 20th September 1985

• Earthquake registering 8.1 and 7.5 on the Richter scale

Cause

The Cocos Plate and the North American Plate moved towards each other, undergoing subduction. As a result of friction, enormous stress accumulated in the rocks. When the rocks jerked free, an earthquake occurred.

Effects

Along the coastal lines, seismic waves or tsunamis as high as 20m swamped fishing boats, trawlers and freighters. Mexico city was the worst hit. Hundreds of buildings such as office blocks and hotels collapsed. Many people were trapped and killed. Other structures were badly damaged and had to be demolised. Communications were disrupted as telephone links, roads and railways were destroyed. Fires broke out. Even sewers broke, discharging their contents onto the shattered roads. The whole city was completely destroyed. The death toll was 20,000. Many more were seriously injured. 30,000 people were left homeless.

Why Mexico City was severely damaged

Mexico City was built on thick layers of soft silt and peat of a lake. This did not provide a good foundation for the city. The soft, unsteady material amplified the vibrations, causing the ground to shake. The vibrations caused the grounds to lose strenght by liquefaction and many buildings collapsed.

The city was also densly populated. With many people, the rescue teams were not able to tend to all the people because of the damage caused to transportations and communications.

Fires also broke out because of ruptured and damaged gas mains and power lines. It was difficult to put out the fires because of the broken water pipes.

Back to Case Studies