1. Earthquakes and Seismic Waves

2. Introduction
Earthquake = the shaking and trembling that results from movement of rock beneath Earth’s surface
Focus = area beneath Earth’s surface where rock under stress breaks and causes an earthquake
Epicenter = point on the surface directly above the focus
Intro to Earthquakes

3. Seismic Waves
A. Earthquakes produce vibrations called Waves. B. Waves carry energy. C. Seismic waves are vibrations that travel through Earth carrying energy released during an earthquake.
Earthquakes

4. Waves
D. Seismic waves carry energy from an earthquake away from the focus, through Earth’s interior and across the surface.
E. Three main categories of Waves:
Primary Waves (P waves)
Secondary Waves (S waves)
Surface Waves
Brain Pop Waves

5. Waves The first waves to arrive are Primary waves.
P waves compress and expand the ground.
After P waves come Secondary waves.
S waves are seismic waves that vibrate from Side to Side as well as up and down.
When P waves reach the surface, some of them become Surface waves.
Surface waves move more slowly than P or S waves but they produce severe ground movements.

6. Seismic Wave Speeds Refer to Textbook ….page 56 Math Skills
Answer Questions 1 – 4
X axis is Distance from Epicenter and Y axis is arrival time
minutes
4 minutes
2000 = 3.5 minutes and 4000 = 4.5 minutes

7. Waves

8. Measuring Earthquakes
There are at least 3 different measures for rating earthquakes.
Two methods for measurement:
Mercalli Scale
Richter Scale
Mercalli Scale = Rate earthquakes on the level of damage at a certain place
Brain Pop Earthquakes

9. Mercalli Scale

10. Richter Scale
Richter Scale = rating of an earthquake’s magnitude based on the size of the earthquake’s seismic waves
Magnitude is a number geologists assign to an earthquake based on the earthquake’s size
the seismic waves are measured by a seismograph
How does a seismograph work?

12. Richter Scale

13. Comparing Magnitudes Comparing Magnitudes Moderate damage
An earthquake’s magnitude tells Scientists how much energy was released by the earthquake
Earthquakes with a Magnitude of 6 cause?
Moderate damage
32 times the energy of a
Magnitude 5 Quake

14. Locating the Epicenter
Geologists use seismic waves to locate an earthquake’s epicenter.