1. Earthquakes

2. Earthquakes
Result from abrupt movements on faults or fractures in the Earth’s lithosphere
Energy is slowly accumulated in rocks
Two plates slide past one another
Parts of plates stick because of friction
As the rest of the plate continues to slide, more friction energy is created.

3. Seismic waves
Focus – point where first seismic waves begin (center of earthquake)
Epicenter – point on Earth’s surface directly above focus.

4. Waves
Waves – vibrations that move outward from focus (“center” of earthquake)
2 types of waves
1. Body waves – travel though Earth’s interior
-Primary waves (P-wave): highest velocity, first to be detected
-Secondary waves (S-wave): travel slower and are detected afterwards
2. Surface waves – travel on Earth’s surface

5. P Wave
S Wave

6. Surface Waves
The two surface waves are Love (L) waves and Raleigh waves.
L-waves cause the ground to move side to side.
R-waves roll like an ocean wave causing the ground to go up and down

7. Measuring Earthquakes
Seismograph – measures and records vibrations of a earthquake.
Information displayed on a Seismogram
Distance vs. time graph
P wave faster than S wave

8. Seismogram

9. Using the Seismogram
The distance between the beginning of the first P wave and the first S wave tells you how many seconds the waves are apart.
This number will be used to tell you how far your seismograph is from the epicenter of the earthquake.
Using three seismographs, a map and a compass, the epicenter can be located.

10. Locating the epicenter of an earthquake

11. Richter Magnitude Scale
Developed by Charles Richter
Scale that assigns a single number to quantify the amount of seismic energy released by an earthquake.
Base-10 logarithmic scale, which means an earthquake that measures 5.0 on the Richter scale has a shaking amplitude 10 times larger than one that measures 4.0.

13. Effects Intensity is a measure of the damage caused by an earthquake.
It is measured by a number on the modified Mercalli scale.
The drawbacks are unreliability and differing factors like building materials, distance from quake, foundation of the buildings, opinions of people, etc.
Effects of earthquakes include:
Shaking and ground rupture
Landslides and avalanches
Fires
Soil liquefaction
Tsunami
Floods
Human impacts