1. TOPIC 1:TECTONIC PROCESSES AND HAZARDS
(Lesson 8)

2. 1. Why are some locations more at risk from tectonic hazards?
ENQUIRY QUESTION 1:
1. Why are some locations more at risk from tectonic hazards?

3. Previous lesson Objectives
To have detailed understanding of processes occurring at destructive (convergent) and conservative ( transform)plate boundaries

4. DO THE PLATE BOUNDARY CARD SORT
STARTER
DO THE PLATE BOUNDARY CARD SORT

5. EARTHQUAKES!!

6. Specification content : Earthquakes
1.1 The global distribution and causes of earthquakes
1.1c The causes of intra – plate earthquakes
1.3 Physical processes explain the causes of tectonic hazards
1.2c Physical processes impact on earthquake magnitude and focal depth (Benioff zone)
1.3a Earthquake waves (P,S and L waves)cause crustal fracturing , ground shaking and secondary hazards
( liquefaction and landslides)

7. Ref: Edexcel Book 1 p8-Booklet:P. ONWARDS
LESSON OBJECTIVES
1.To describe and explain the global distribution of earthquakes
2.To explain how earthquakes are formed at plate boundaries and how intra plate earthquakes are also formed
Ref: Edexcel Book 1 p8-Booklet:P. ONWARDS

8. WHITEBOARD QS
In pairs discuss what you think an earthquake is exactly? How is it caused? Where is it caused and why? When are where was the largest ever recorded magnitude earthquake?

9. FASTEST PERSON ON THE BUZZER………!
When and where was the largest earthquake ever recorded?

10. The largest ever recorded magnitude earthquake!
CHILE May Magnitude 9.5
See Table 1.1 p.9 Hodder :Largest recorded magnitude earthquakes since 1990

11. WHAT ARE EARTHQUAKES?
Earthquakes are vibrations caused by earth movements at plate margins and at major fault lines (fractures of rock strata).Faults are zones of pre- existing weakness in the earth’s crust.

12. BBC Bitesize- earthquake intro

13. Epicentre, focus and seismic waves
The focus is the origin of the earthquake below the ground surface and is the point at which the rock moves
Seismic waves are ripples of energy which start at the focus and cause the ground to move
The epicentre is directly above the focus on the earth’s surface. It is where the earthquake is most strongly felt.

14. A Cross section of an earthquake
Copy the diagram and define the term focus, epicentre and seismic waves.
A Cross section of an earthquake
Epicentre
seismic waves
Focus
Fault line

15. Whiteboard Qs What do you think is meant by the terms:
‘ Earthquake Intensity’
‘ Magnitude’ ?????????

16. KEY TERMS:
EARTHQUAKE INTENSITY: This is a measure of the ground shaking. It is the ground shaking that causes building damage and collapse and the loss of life from the hazard
EARTHQUAKE MAGNITUDE: This is related to the amount of movement , or displacement in the fault which in turn is a measure of energy release. It is therefore related to the strength of an earthquake and is measured at the epicentre.
(see Table 1.1. Hodder- largest recorded magnitude earthquakes since 1900)

17. Where do earthquakes happen? SEE TASK IN BOOKLET

18. Why do earthquakes happen?
Earthquakes are caused by sudden movements comparatively near to the earth’s surface
The movements are preceded by a gradual build up of tectonic strain, which stores elastic energy in crustal rocks.
When the pressure exceeds the strength of the fault the rock fractures.
This produces the sudden release of energy, creating seismic waves which radiate away from the point of fracture
The brittle crust then rebounds on either side of the fracture (‘elastic rebound theory’) which is the ground shaking, that is , the earthquake is felt at the surface.

19. Elastic Rebound Theory and Earthquake Generation
Undeformed rocks
Rocks deform due to build up of stress
Rocks fracture and stress is released as seismic waves

20. SEE PREVIOUS PPT NOTES and Edexcel New A level Hodder book p4
Which boundaries are these and what is happening? ‘Tectonics of the Planet Earth secs’ earthquakes at destructive plate margins
SEE PREVIOUS PPT NOTES and Edexcel New A level Hodder book p4

21. BBC Earthquake animation

22. Q:Where do many earthquakes form? A: At all major plate boundaries!
We know there are three types of plate boundaries: Divergent, Convergent and Transform. Movement and slipping along each of these types of boundaries can form an earthquake.
Depending on the type of movement, the earthquakes occur in either a shallow or deep level in the crust.
The majority of tectonic earthquakes originate at depths not exceeding tens of kilometers.
In subduction zones, where old and cold oceanic crust descends beneath another tectonic plate, “Deep Focus Earthquakes” may occur at much greater depths (up to seven hundred kilometers!).
These earthquakes occur at a depth at which the subducted crust should no longer be brittle, due to the high temperature and pressure. A possible mechanism for the generation of deep focus earthquakes is faulting.
Earthquakes may also occur in volcanic regions and are caused there both by tectonic faults and by the movement of magma (hot molten rock) within the volcano. Such earthquakes can be an early warning of volcanic eruptions.
Figure showing the tectonic setting of earthquakes

24. Earthquakes form at Conservative Margins

25. e.g.San Andreas Fault, USA
The San Andreas Fault is the border between two tectonic plates — the North American Plate and Pacific (Nazca) Plate

26. Earthquakes also form at Constructive(Divergent) plate boundaries e. g
Earthquakes also form at Constructive(Divergent) plate boundaries e.g. the Mid Atlantic Ridge(MAR)
AS SECTIONS OF THE CRUST SLIDE PAST ONE ANOTHER, SHALLOW FOCUS EARTHQUAKES ARE CREATED, ORIGINATING CLOSE TO THE SURFACE