On Tuesday, September 19, a magnitude 7.1 earthquake shook Mexico City, toppling buildings and crushing cars. There are now more than 200 dead. The earthquake hit about 100 miles away from Mexico City at 1:00 p.m. local time. (See heartbreaking photographs of the destruction.)
More About Earthquakes
Earthquakes, also called temblors, can be so tremendously destructive, it’s hard to imagine they occur by the thousands every day around the world, usually in the form of small tremors.
Where Do Most Earthquakes Occur?
Some 80 percent of all the planet's earthquakes occur along the rim of the Pacific Ocean, called the "Ring of Fire" because of the preponderance of volcanic activity there as well. Most earthquakes occur at fault zones, where tectonic plates—giant rock slabs that make up the Earth's upper layer—collide or slide against each other.
These impacts are usually gradual and unnoticeable on the surface; however, immense stress can build up between plates. When this stress is released quickly, it sends massive vibrations, called seismic waves, often hundreds of miles through the rock and up to the surface. Other quakes can occur far from faults zones when plates are stretched or squeezed.
Earthquake Magnitude Ratings and Their Impacts
Scientists assign a magnitude rating to earthquakes based on the strength and duration of their seismic waves. A quake measuring 3 to 5 is considered minor or light; 5 to 7 is moderate to strong; 7 to 8 is major; and 8 or more is great.
On average, a magnitude 8 quake strikes somewhere every year and some 10,000 people die in earthquakes annually. Collapsing buildings claim by far the majority of lives, but the destruction is often compounded by mud slides, fires, floods, or tsunamis. Smaller temblors that usually occur in the days following a large earthquake can complicate rescue efforts and cause further death and destruction.
Loss of life can be avoided through emergency planning, education, and the construction of buildings that sway rather than break under the stress of an earthquake.
Warning: Some of the photos below contain graphic imagery.