1. Earthquakes and Seismic Waves

2. Earthquake – shaking and trebling that results from the movement of rock beneath Earth’s surface. Plate movement causes earthquakes from stress and faults in Earth’s crust. When the rock breaks earthquakes happen

3. Most Earthquakes start in the lithosphere about 100 kilometers of Earth’s surface.
Focus – area beneath Earth’s surface where rock that is under stress breaks, causing an earthquake
Epicenter – the point on the surface directly above the focus

4. Seismic waves are vibrations that travel through Earth carrying the energy released during an Earthquake
Seismic waves move out from the focus in all directions through the interior and across the surface

6. 3 main seismic waves
P Waves – Primary waves
First to arrive
They compress and expand the ground
Can damage buildings
Travel through solid and liquid

7. S Waves – Secondary waves
Seismic waves that vibrate from side to side as well as up and down
Travel through solid not liquid

8. Surface Waves – when P waves and S waves reach the surface, some become surface waves.
Move slower than P waves and S waves, produce severe ground movement
Can make the ground roll like ocean waves

10. Measuring Earthquakes
Mercalli Scale
Rates Earthquakes by the level of damage at a given place
12 steps
I-III people notice vibration
IV-VI slight damage
VII-IX Moderate to heavy damage (buildings off foundations or destroyed)
X-XII Great destruction (cracks in the ground, waves seen on surface)

12. The Richter Scale
Magnitude a number geologists assign based on the earthquake size
Geologists measure seismic waves and fault movement with a Richter scale
Seismic waves are measured by a seismograph
More accurate for small, nearby earthquakes

14. Moment Magnitude Scale
Rating system that estimates the total energy release
Rates near or far earthquakes
Use data from the seismographs, kind of seismic waves, how strong they were, movement along the fault and the strength of the rocks that broke

15. Locating the Epicenter
Use seismic waves to locate an earthquake’s epicenter
P waves arrive first, then S waves close behind
They use the arrival time between the P waves and S waves, the farther away the greater the time between the arrival
They then draw three circles using data from different seismographs, where they all intersect that is the epicenter.

16. News Report As a television news reporter, you are covering an earthquake rated between IV and V on the Mercalli scale. Write a short news story describing the earthquake’s effects. Your lead paragraph should tell who, what where, when and how. (The Mercalli Scale on page 55 Figure 9 will help)