1. 1. How do earthquakes travel through the earth? By seismic waves
National Geo Clip
1. How do earthquakes travel through the earth?
By seismic waves
2. On what device do scientists record earthquakes?
A seismometer or seismograph
On what scale do scientists measure the magnitude of earthquakes?
The Richter scale
Each number higher on the Richter scale releases how much more energy than the number below it?
30 times the energy (10 times the shaking)
5. How many earthquakes occur each year around the world?
100,000 (but only 1,000 cause damage)

2. Kaupapa / Learning Outcome
At the end of todays lesson I can explain
how earthquakes happen
the different types of waves associated with an earthquake
how a seismograph works

3. Earthquakes
An earthquake is the release of energy that has been stored in rock due to the gradual movement of the earth’s crust and results in damaging seismic waves being created

4. Focus vs Epicentre Focus Epicentre
Where the fault deep in the crust actually started to break
Epicentre
The point on the surface directly above the focus

5. What moves? Earthquakes are caused by movement along a fault
A Fault is any crack in rock that has movement along it
*Reminder*
A fault can occur anywhere, but they are normally near tectonic plate boundaries

6. What this means

7. Types of Earthquake Waves
3 different types of waves move through the Earth’s crust during an earthquake

8. Types of Waves
P-Waves or primary waves are the first waves to hit as they move the fastest (8km/s). They squeeze and stretch the rock.

9. Types of Waves
The next waves to hit are the secondary waves (S-Waves). These waves move at 5km/s and make the ground shake up and down as well as from side to side.

10. Types of Waves
Traveling at 4km/s are the last waves to hit, the L-Waves. These waves do the most damage as they travel near the surface of the crust.

11. Types of Waves All three together.
Now do the worksheet on P, S, L waves

12. Features
P- Waves
S - Waves
L - Waves
Full Name
Primary
Secondary
Long
Action
Push / pull
Up / down / sideways
Rolling
Travelling Speed
Speed km/s
Speed km/s
Speed km/s
Arrival
First
Second
Third
Damage Level
Minor
Moderate
Major
In Water
Pass through
Absorbed
Location
In crust
Surface only

14. Seismograph

15. The energy ________ travels outwards as _____
The energy ________ travels outwards as _____. The point in the Earth’s crust where this happens is called the _____, the point directly above the focus on the Earth’s surface is called the _________. Seismologists use ___________ to determine the magnitude and ________ of earthquakes.
released
waves
focus
epicentre
seismographs
location
seismographs focus location
waves epicentre released

16. Earthquakes – The Scales
Earthquakes are measured on different types of scales.
The Richter Scale – Measures the magnitude of the earthquake (how much energy is released) on a scale of 1 to 10.
Each step up represents 10 times more energy released
Problem is, it doesn’t really work…

17. Earthquakes – The Scales
Instead of the Richter scale a similar scale, called the Moment Magnitude scale, is used
This scale is similar to the Richter scale but each step up represents 32 times more energy released
A step from 5 to 6 represents an increase of 32 times the energy
A step from 5 to 7 represents an increase of almost 1000 times the energy

18. Earthquakes – The Scales
A more objective method is to measure the effect on humans and buildings
The Modified Mercalli Index – Measures the damage done at a particular location.
How much it shook
Everyone will have a slightly different value for where they lived

19. Modified Mercalli Index
MM 1: Imperceptible Barely sensed only by a very few people.
MM 2: Scarcely felt Felt only by a few people at rest in houses or on upper floors.
MM 3: Weak Felt indoors as a light vibration. Hanging objects may swing slightly.
MM 4: Largely observed Walls may creak, and glassware, crockery, doors or windows rattle.
MM 5: Strong Generally felt outside and by almost everyone indoors. Most sleepers are awakened and a few people alarmed.
MM 6: Slightly damaging Felt by all. Glassware and crockery break. Slight non-structural damage may occur.
MM 7: Damaging General alarm. A few weak buildings are damaged.
MM 8: Heavily damaging Alarm may approach panic. A few buildings are damaged and some buildings destroyed.
MM 9: Destructive Some buildings are damaged and many weak buildings are destroyed.
MM 10: Very destructive Many buildings are damaged and most weak buildings are destroyed.
MM 11: Devastating Most buildings are damaged and many buildings are destroyed.
MM 12: Completely devastating All buildings are damaged and most buildings are destroyed.