Earthquake Survivors Tell Their Stories

ANATOMY OF AN EARTHQUAKE

"WE ARE SO ACCUSTOMED TO LIVING ON SOLID EARTH THAT WHEN THAT BEGINS TO SHAKE THE MIND IS OVERWHELMED." -"THE VIOLENT EARTH."

"EARTHQUAKES  are among the most destructive and powerful forces in nature," notes The Word Book Encyclopedia.  That statement is  no exaggeration, for the energy released by a severe quake may be 10,000 times greater than that generated by the first atom bomb! Adding to the terror is the fact that earthquakes can happen in any climate, during any season, and at any time of the day. And although scientists may have some idea where powerful temblors are likely to occur, they cannot specify when. 

Earthquakes occur as a result of masses of rock changing position below the earth's surface.  This type of activity goes on continuously. Often, the shock waves that result  are not powerful enough to be felt at  the earth's surface, but they can be detected and recorded by a seismograph.  At other times, enough rock breaks and enough shift takes place to shake the surface violently. 

But why is there constant movement in the earth's crust? "An explanation is to found in plate tectonics, a concept which has revolutionized thinking in the Earth's sciences, "says the National Earthquake Information Center (NEIC).  "We now know that there are seven major crustal plates, subdivided into a number of small plates," NEIC adds,  "all constant motion relative to one another, at rates varying from 10 to 130 millimeters [three eighths of an inch to five inches] per year."  Most earthquakes, NEIC says, are confined to narrow belts that define the boundaries  of the plates.  This is where 90 percent of major earthquakes are likely to occur.

Next time: ANATOMY OF AN EARTHQUAKE/Magnitude and intensity.

From the Awake! magazine