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

2. 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

3. 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

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

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

7. 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

8. 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

9. 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!

12. 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

13. 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!

14. 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

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

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