Dynamic+crust

THE DYNAMIC CRUST

What causes earthquakes? Earthquakes occur when stress builds up in zones of weakness in the earth’s crust. These areas are known as //faults.// The released energy from a broken fault radiates in all directions. The //epicenter// is the term used for the point directly over the earthquake on the surface. __ Measuring Earthquakes __ A Seismologist is a person who studies earthquakes. The scientific tool they use is called a seismograph. During an earthquake, the earth shakes. How much it shakes is called the //magnitude.//

__ Earthquake waves __ • P-waves are also known as //primary// waves. This is because they travel the fastest. • P-waves are also known as compressional waves which can be thought of as a “push/ pull” movement. • P-waves travel through all materials. • S-waves are also known as //secondary// waves because they travel slower and ALWAYS arrive after P-waves. • S-waves travel like light waves in that they are “side to side” waves. • S-waves only travel through Solids (S=S).

__ Locating an epicenter __ This has to do with figuring out the difference in P-wave and S-wave arrival times. The closer (in minutes and seconds) they are together, the closer you are to the epicenter. Conversely, the farther the time between P-waves and S-waves, the farther you are located away from the epicenter.

Brain Teaser: If they occur at the same exact time, where are you located???