Guest Post from:
PETER T. ERDELYI & ASSOCIATES, INC. • Architectural Engineering & Structural Design since 1974
1975 Sawtelle Blvd Ste 175 • Los Angeles, CA 90025 www.erdelyi.com
Here’s the next serving of our bite-sized engineering stories as they happened at Peter T. Erdelyi & Associates.
SHAKING ALL OVER
In light of the recent earthquakes I thought that sharing a few lesser known facts will help to understand what earthquakes are actually all about.
The earthquakes of California are caused by the movement of huge blocks, or plates, of the earth’s crust – the Pacific and North American plates. The Pacific plate is moving northwest, scraping horizontally past the North American plate at a rate of about 2 inches per year, which is about the rate your fingernails grow. (This maybe explains why my wife has to go to the manicurist so many times a year.:)) You can compare this movement to when you snap your fingers. Before the snap, you push your fingers together and sideways. Because you are pushing them together, friction keeps them from moving to the side. When you push sideways hard enough to overcome this friction, your fingers move suddenly, releasing energy in the form of sound waves that set the air vibrating and travel from your hand to your ear, and you hear the snap. The same process goes on in an earthquake. Slow movements in the earth’s outer layer push the sides of the faults together. The friction across the surface of the fault holds the rocks together so they do not slip immediately when pushed sideways. Eventually enough stress builds up and the rocks slip suddenly, releasing energy in waves that travel through the rock to cause the shaking that we feel during an earthquake. [Read more…]