2. In the Beginning It was not until the 1960s, when the secrets of the deep ocean floor began to be revealed, that scientists found the explanation of the cause of earthquakes. This became know as the theory of plate tectonics.

3. Tectonic Theory The tectonic theory says that the earth's surface is fragmented into huge slabs called tectonic plates. These chunks of move across its surface in response to forces and movements deep within the planet The plate boundaries, where plates collide, grind past each other, or move apart, are areas of intense geological activity.

4. Cause Most volcanoes and earthquakes occur at these boundaries. Earthquakes happen when the pressure between two tectonic plates is so intense that the plates shift their positions suddenly, causing the earth to shake

5. During a severe earthquake, the ground can shake so violently that entire cities are reduced to rubble Sometimes these disasters kill thousands of people. Most of the time they cause little damage to people and property.

6. Aftershocks For months after a quake people may feel unsettling aftershocks; small tremors that follow a major earthquake

7. Longest Tremor! The Alaskan earthquake of March 27, 1964, lasted 4 minutes. Most last less than a minute.

8. http://www.youtube.com/watch?v=VSgB1IWr6O4

9. K.S. What is an aftershock?