1. Earthquakes

2. Focus
The point beneath Earth’s surface where rock breaks under stress and causes an earthquake

3. Epicenter
The point on Earth’s surface directly above an earthquake’s focus

4. Seismic Waves

5. Seismic wave generation
Seismic waves are released when rocks that are under pressure bend and then break, releasing energy
The point at which the rock breaks is called shear strengh
Elastic rebound - When the rocks break and go back to their original shape releasing energy

6. Seismic Waves
A vibration that travels through Earth carrying the energy released during an earthquake

7. What determines how much the ground shakes during an earthquake?
How close a location is to the epicenter
The types of rock and soil surrounding the epicenter determines how much the ground shakes

8. What are the different kinds of seismic waves?
There are three types of seismic waves:
Primary Waves (P waves)
Secondary Waves (S waves)
Surface Waves

9. An earthquake sends out two types of waves P waves and S waves
When the waves reach Earth’s surface at the epicenter, surface waves develop.

10. Primary Waves

11. Primary Waves (P Waves)
A type of seismic wave that compresses and expands the ground
The first wave to arrive at a seismomoter

12. P wave movement P waves compress and expand like an accordion
When P waves arrive they vibrate the particles of the crust forward and back along the path of the wave

13. Secondary Waves

14. Secondary Waves (S Waves)
A type of seismic wave that moves the ground side to side

15. How are P waves different from S Waves?
P waves compress and expand the ground
These waves cause buildings to contract and expand
P waves travel through solids and liquids
S waves vibrate from side to side
These waves vibrate from side to side and thrust the ground up and down, or back and forth
S waves can not move through liquids

16. Surface Waves

17. Surface Waves
A type of seismic wave that forms when P waves and S waves reach Earth’s surface
Surface (L-waves) cause the most damage

18. Detecting Seismic Waves

19. Seismograph
A device that records ground movements caused by seismic waves as they move through Earth

20. Seismometers Old School vs. New School

21. Measuring Earthquakes

22. The Mercalli Scale

23. Mercalli Scale
A scale that rates earthquakes according to their intensity and how much damage they cause

24. Magnitude
The measurement of an earthquake’s strength based on seismic waves and movement along faults

25. The Richter Scale

27. Richter Scale
A scale that rates seismic waves as measured by a particular type of mechanical seismograph

28. How are the Mercalli scale and the Richter scale similar
How are the Mercalli scale and the Richter scale similar? How are they different?
Both measure the strength of an earthquake
The Mercalli scale measures the strength in terms of extent people notice the earthquake and the amount of damage caused
The Richter scale measures the size of seismic waves

29. Locating the Epicenter

30. P-S interval

31. How do scientists calculate how far a location is from the epicenter of an earthquake?
Scientists calculate the difference between arrival times of the P waves and S waves
The further away an earthquake is, the greater the time between the arrival of the P waves and the S waves

32. Steps to finding an Earthquakes epicenter
Step 1: Calculate the S-P interval
This is how much time is between the 1st P-wave and the 1st S-wave

33. Step 2- determine distance to epicenter using a time-travel graph

34. Step 3- map circumference showing where EQ could
To do this, find the distance to the epicenter and draw a circle at that distance around the seismograph location using the scale on your map.

35. The point where all three circles intersect is the epicenter
Houston
800 Km
Savannah
900 km

36. Direct vs. Indirect Damage
Direct Hazards- damage caused by the earth shaking
Collapse of buildings, broken power lines, pipelines, roads and bridges
Indirect Hazards- a side-effect of the ground shaking
Fire, landslides, tsunami

37. Tsunami
Travel at great speeds which make warnings difficult (1000km/hr)
Not very high waves on the ocean, only a m, but can be more than 30 m high when crashing on shore

38. What effects the amount of damage caused during an earthquake?
Duration of Shaking
Direction of Motion
Underlying Earth Materials
Loose, wet soil will sustain more damage than bedrock

39. Designing Earthquake Resistant Structures