Imagine you are sitting in your desk at school and the ground begins to shake, books are knocked off shelves and the lights begin to swing. This rumbling is what happens when an earthquake occurs.
Earthquakes are one of the deadliest natural disasters. All in the span of two weeks, Mexico suffered through two large earthquakes, with the predicted death toll at 1,000 people.
Thirty-two years ago, on September 19th, an earthquake struck Mexico City, killing 10,000 people. This year, on the anniversary of this tragedy, an earthquake hit Mexico City with a magnitude of 7.1. Only twelve days earlier, on September 7th, an earthquake with a magnitude of 8.1 struck Mexico, the most powerful quake to hit the country in a century.
What Causes Earthquakes?
These earthquakes in Mexico were caused by plate tectonics. The theory of plate tectonics is that the lithosphere (the outer layer of the earth) is separated into many pieces, or plates, that shift across the earth's surface like cracked ice on a lake. The shifting of tectonic plates is caused by the liquid inner core of Earth flowing underneath them. These plates interact with each other in areas where they meet, called fault lines.
Mexico is located above a type of fault line called a subduction zone. A subduction zone is an area where the ocean floor forces its way beneath the edge of a continent. In Mexico, the Cocos tectonic plate forces its way beneath the continental edge of North America.
When the two plates grind against each other, sometimes they get stuck, or locked in place. Despite them not being able to move, they continue to push against one another over the course of years. Once enough energy builds up between the locked plates, in a matter of seconds, one plate breaks free and shifts up or down. This results in an earthquake or tsunami.
Mexico City is more likely to have earthquakes of large magnitudes because it sits on an ancient lake bed filled with sediment. The sediment magnifies the tremors, behaving similarly to a bowl of jelly when shaken.
Are They Related?
Both recent earthquakes in Mexico occurred deep within the Cocos plate, rather than on the surface, which significantly weakened the impact of their tremors. The first quake hit off the southeast coast of Mexico city, causing a substantial amount of damage. However, the proximity of the second quake's epicenter, the origin of the quake above Earth’s surface, to Mexico City resulted in a much larger impact.
This difference in location and large magnitude of the quakes has led scientists to believe that these two quakes were not related. Over the past week, Mexico City has continued to endure aftershocks or small tremors caused by a previous earthquake. The good news is that an earthquake of high magnitude is unlikely to happen again anytime soon in the Mexico City area.