The Science Behind Earthquakes: What Causes Them?
You may have noticed that your left elbow always seems to twinge about five seconds before an earthquake, or that your Chihuahua tends to run in counterclockwise circles 10 times just before one hits, but the truth is that no one, scientist or animal, has yet been able to predict an earthquake's occurrence. We may not know when they're coming, let alone how to stop them, but science has been able to determine what causes them. Trying to predict an earthquake's arrival may not yet be possible, but learning about what causes them and remaining ever vigilant for the next one is vital.
The Earth's Ballet
The earth's surface is comprised of approximately 20 ever-moving tectonic plates, which all go in different directions, angles and speeds in a type of continuous, albeit awkward, ballet. When these plates become stretched out or squeezed tight, the pressure causes massive rock formations to form around their edges, which are called plate boundaries. The rocks create friction as the tectonic plates continue their slow-moving, slip-slide past and around each other, sometimes sticking together in spots even as the plates continue to move. As the pressure builds, the sticking rocks ultimately give way and shift with massive force, exploding the earth's crust upward in an attempt to reduce the pressure and causing a fault or crack in the earth's surface. The outward waves of energy that result cause the shaking, rocking and rolling we have come to know of as earthquakes.
Where Most Earthquakes Happen
Except for the very deepest earthquakes, most occur along geologic fault lines. One of the most famous faults, the 810-mile-long San Andreas, goes through the entire state of California and was responsible for the Great San Francisco Earthquake of 1906, which caused catastrophic destruction and loss of life. The San Andreas Fault is where the North American and Pacific Plates touch, often with devastating consequences.
Faults range in size from microscopic to many miles long. The longest faults can result in massive earthquakes when the plates below them collide and rupture. The highest magnitude of any earthquake yet recorded occurred in Chile in 1960, when the Nazca Plate descended below the South American Plate, causing a massive earthquake with a magnitude of 9.5, as well as a series of destructive foreshocks and aftershocks.
Earthquakes can also be caused by people, though these tend to be localized and smaller in nature. Mining, impoundment of reservoir water and wastewater disposal may all occasionally be at cause, but do not rival nature's fury when the big ones hit.
What Can We Do About Them?
We can't predict them but we can prepare for them. Having your family, friends and co-workers participate in earthquake drills, perusing your home to determine its structural safety and creating safe, indoor spaces can all contribute to increased safety during and after an earthquake occurs. Learning all you can about earthquake safety, understanding their causes and teaching others what you've learned is a big safety, as well as an educational plus.
Resources:
Southern California Earthquake Center
U.S.G.S. Earthquakes Hazards Program
Corey Whelan is a freelance writer in New York. Her work can be found at Examiner.com.
To learn more, visit CBS Los Angeles's Earthquake Resource Center
