Seismic Waves Just like doctors use an MRI, CT scan, or an x-ray to see inside our bodies, geologists use seismic waves. Mapping the Earth’s Interior Allows scientists to see how energy travels from the point of an earthquake through the Earth’s interior. • Travel outward in all directions • Energy is passed from one rock particle to another like dominoes
Correlate • Density • Speed Or • Density • Velocity
Types • 2 Main Types of Waves: • Body • Surface • Types of Motion • Back and forth • Side to side • Up and down • Body Waves – travel through the body of a medium • 2 types: • P Waves (primary) • S Waves (secondary) • Surface Waves – travel along the surface of a body • 2 types: • Love Waves • Rayleigh Waves
P Waves Back and Forth Parallel to Wave Direction • Fastest • traveling at about 6 to 7 kilometers (about 4 miles) per second • arrive first at the seismometer. • Squeeze and un-squeeze earth materials as they travel • produces a change in volume for the material • Bend slightly when they travel from one layer into another • Can move through a solid, liquid, or gas • move faster through denser or more rigid material • slow down when they pass through the liquid, outer core • Create a shadow zone as they slow as they pass through the liquid core arriving later and further away than expected
S Waves Side to Side Perpendicular to Wave Direction • Half as fast as P-waves • traveling at about 3.5 km (2 miles) per second • arrive second at seismographs • Produce a change in shape for the earth materials they move through • Can only move through solids • since solids resist a change in shape • cannot travel through liquid • Create a shadow zone since they cannot move through the core
When an earthquake occurs, both S and P waves radiate outward. Because the rocks increase in density as depth increases, the path of the waves bends.
S waves are detected over a little more than 1/4 of the earth's surface resulting in a S wave shadow zone. Evidence: liquid core P waves are detected on the opposite of the Earth, but a P wave shadow zone is created from 103o to 142o. Evidence: liquid core Explanation: as the waves move through the liquid core they are bent or refracted.