From NationalGeographicVideo, produced by National Geographic
Witness the destructive power of earthquakes, from home videos taken during a tremor. Video goes inside the Earth to show how an earthquake starts. Earth is covered by plates, when the plates are moved by the heat of the inner Earth, they grind against each other along lines called faults. When the plates motion is blocked stress builds up, finally the fault gives way. The released energy moves through the Earth called seismic waves. Seismic waves are measured by scientists on seismographs. Only about a thousand of these waves is strong enough to cause damage. About 10,000 people die each year in earthquakes. The strongest earthquake to date in North America measured 9.2, and was in Alaska on March 28, 1964. Video is good quality and has good information. Good for elementary grade and middle school students.