2. Earthquakes

3. Case Studies
Haiti 12th Jan 2010
New Zealand 3rd Sept 2010
7.0 magnitude
Focus depth: 8.1 miles deep
Fault line that was previously undetected
Epicentre: 25 miles from Port au Prince
Deaths: 230,000
7.0 magnitude
Focus depth: 7.5 miles deep
The Alpine and the Hope faults
Epicentre: 35 miles from Christchurch
Deaths: 0
Why with so many similarities between the two earthquakes, did so many die in the Haiti earthquake?

4. Reasons: Poor nation (poorest country in the Northern Hemisphere)
Haiti 12th Jan 2010
New Zealand 3rd Sept 2010
Poor nation (poorest country in the Northern Hemisphere)
Little experience with earthquakes (previously undetected fault line)
Non-existent building standards
4.53pm lots of people out in the streets
Wealthy developed country
More experience with earthquake (active fault line)
High construction codes
4.35am people asleep in their beds

5. Haiti
6mts after the earthquake?

6. Earthquakes
Definition: Earthquakes are vibrations or tremors in the earth’s crust, and are caused by the movement of the plates which makes the crust stretch and tear. This increase in stress and pressure is greater than the strength of the rocks which suddenly give way along a fault line in the crust.

7. Earthquakes
Tremors: shock waves which travel out from the origin or focus of the earthquake
Focus: The point deep in the crust at which an Earthquake begins.
Epicentre: Directly above the Focus on the surface is the Epicentre. The Earthquake is strongest here.

8. P and S waves
When an earthquake occurs, it releases energy in the form of seismic waves that radiate from the earthquake focus in all directions.
The different types of energy waves shake the ground in different ways and also travel through the earth at different velocities.
The fastest wave, and therefore the first to arrive at a given location, is called the P wave. The P wave, or compressional wave, alternately compresses and expands material in the same direction it is traveling.
The S wave is slower than the P wave and arrives next, shaking the ground up and down and back and forth perpendicular to the direction it is traveling.

9. Earthquake Waves Two types:
P waves or compression waves, shake the ground back and forth in the same direction as the wave is moving. These are very fast and do little damage, they can pass through a building in less than a second.
An S wave or shear wave, shakes the ground back and forth perpendicular to the direction the wave is moving. They arrive after the P waves as they travel more slowly, and can damage buildings.

10. Surface waves
A surface wave is a seismic wave that is trapped near the surface of the earth. (The Love and Rayleigh waves)

11. Earthquake Depth
Shallow earthquakes: Less then 70km below the surface (mid-ocean ridges, continental-continental plate collision & conservative plate boundaries)
Intermediate earthquakes: km below the surface (oceanic-continental plate collisions)
Deep earthquakes: Greater then 300km below the surface (oceanic-oceanic plate collision)

12. Measuring and recording Earthquakes
Seismographs
The Richter Scale
The Modified Mercalli Scale
Moment Magnitude Scale

13. Seismograph
Sensitive instruments called seismographs record earthquake waves
Global Seismic Networks (GSN) is a web of 128 recording stations across the world
These detect earthquakes and help monitor nuclear tests

15. Seismograph Reading
P waves
S waves

16. Richter Scale
A scale which was devised by Charles F. Richter. It is a measure of the amount of energy released by an earthquake.

17. Moment Magnitude Scale
The Moment Magnitude Scale is the successor to the Richter Scale and is today used by seismologists.
It measures the energy produced by earthquakes. It again goes from 1 upwards. At each step about 32 times more energy is released than at the previous step.

18. Modified Mercalli Scale
A measure of the observed effects of an earthquake
Seismologists seek information from people on the severity of earthquake effects
Roman numbers i to xii are used to show intensity of the earthquake

19. Modified Mercalli Scale