Seismic Waves 3d - Students know why and how earthquakes occur and the scales used to measure their intensity and magnitude.

Energy travels throughout Earth…not just at the surface! When rocks break and an earthquake occurs a significant amount of stored energy is released. Seismic waves - energy that travels through Earth in the form of waves Energy travels throughout Earth…not just at the surface! The waves start at the focus – the area in the crust where the rock breaks Seismic waves travel outward from this point This outward traveling energy causes earthquake damage

Focus The focus is the starting point of an earthquake It is where the rock actually snaps and motion occurs Most of the time it is underground

Epicenter Spot on Earth’s surface directly above the focus Experiences the most energy during the earthquake

Waves of Energy! Types of Waves 3 types of waves: Primary waves (P-Waves) Secondary waves (S-Waves) Surface Waves

Primary Waves P-waves Fastest – arrive at a location before any other waves Push-pull waves –pushes and pulls at rock as it travels through it Pass through solids and liquids – travels through magma Because they travel through liquids and solids, P-waves can travel through the liquid and solid interior of Earth and affect locations on the other side of Earth

Secondary Waves S-waves Arrive second at a location Slow waves – travel at slow speeds (about ½ of Pwaves) Shake waves – vibrate and move up and down Solids-only – travels through solid rock only

Moves both up and down and side to side! Surface Waves Does not travel through Interior of Earth! Travel on the surface of Earth Slowest type of wave MOST DESTRUCTIVE! Moves both up and down and side to side!

How are Waves Measured? Scientists measure waves by using a seismograph It draws a zigzag pattern that depicts the seismic waves It creates a printout called a seismogram

By looking at the seismogram, two conclusions can be made Speed of the waves Distance to the Earthquake Epicenter The greater the distance between the S and P waves, the further away the earthquake epicenter!

Distance to Epicenter Use a time-travel graph Find the time between the P and S wave from seismogram. Use the time-travel graph and find spot on the graph where the S and P waves are separated by time you found in step 1. Drop a line straight down at the location and read the distance off graph. It shows the average travel times for P & S waves The difference in arrival times is used to calculate the distance from the seismograph station to the earthquake epicenter

Once distance is know, that distance (radius) can be plotted on a map from the seismic station picking up the waves.

How many seismic stations are needed to find epicenter? Once 3 stations map radius, the exact epicenter is where the 3 circles intercept