E a r t h q u a k e s

What are they? Earthquake – The shaking and trembling that results from the movement of plates beneath the earth’s surface. *Earthquakes happen because of stress………. “Stress” is a force that adds energy. The earth stores this energy in rocks until things eventually break, adjust or change shape – Then all of this energy is released at once! Interesting fact: The earth is never still! Everyday, there are about 8,000 earthquakes worldwide - some large, most small.

Some earthquake terms….. Fault- a break in the earth’s crust where slabs of crust slip past each other – usually along plate boundaries. Focus- where in the lithosphere an earthquake begins. This is where the stress or energy is released. Epicenter – The place on the earth’s surface directly above the focus.

How do we know where an earthquake’s focus and epicenter are? Just like in water, energy travels through the earth in waves. These seismic waves travel outward from the focus of an earthquake in all directions.

Scientists called seismologists measure and study these waves Scientists called seismologists measure and study these waves. They can determine when and where an earthquake occurred as well as how powerful it was. They can also tell what these waves travel through giving us accurate information about the earth’s interior.

Seismographs measure and record the vibrations of seismic waves Seismographs measure and record the vibrations of seismic waves. There are two main types of seismic waves measured: P- Waves and S- Waves “P” waves stand for primary waves because they travel the fastest and arrive first! “S” waves stand for secondary waves because they travel slower and arrive second! *Because scientists know exactly how fast these travel, they can take the difference in arrival times of the two and calculate how far away the event occurred. Once P and S waves have reached the earth’s surface they become what are called surface waves. These waves move very slow but produce the most ground movement and damage.

The effect of an earthquake can be measured in two ways: Magnitude Refers to the amount of energy released at the earthquake’s focus Intensity Refers to the observed effect an earthquake has on people, buildings and natural features.

When water is suddenly displaced it has a great affect When water is suddenly displaced it has a great affect. When this happens on a large scale or in a very large body of water the result is called a Tsunami. So…… A Tsunami is caused by nothing more than a large amount of water being displaced (taken up) by something very quickly. How can water be displaced on a large scale? Why are Tsunamis so dangerous? Why do most occur in the pacific ocean?

Some ways a tsunami can be triggered: Meteor impact Underwater Earthquake Landslide

As water gets shallower, the wave grows taller As water gets shallower, the wave grows taller. It has no where else to go but “up”. All low areas near coasts are in danger. Even a small Tsunami can destroy a large area.