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

27. Or at Destructive Plate Boundaries…..
5. Fold mountains form as sediments are crumpled up on leading edges of continental masses
1.Convection currents cool and descend causing two plates to be pulled towards each other( or by ‘slab pull theory’)
Oceanic crust denser/heavier but thinner forced beneath lighter continental crust
Continental Crust
Oceanic Crust
4. Could lead to rising magma (molten rock) – volcanic eruption
3.Friction causes heat which melts ocean crust in to mantle in the BENIOFF ZONE which causes earthquakes (SEE NOTES..)
2. Crust Melts in subduction zone and creates a deep ocean trench

28. SUBDUCTION ZONE
Subduction zone - where two tectonic plates move towards one another subduction can occur. This involves an oceanic plate sliding beneath either a continental plate or another oceanic plate.
Subduction zones are often noted for their high rates of volcanism, earthquakes, and mountain building. This is because subduction processes result in melting of the mantle that produces a volcanic arc as relatively lighter rock is forcibly submerged

29. Shallow-focus and deep-focus earthquakes
The majority of tectonic earthquakes originate at the Pacific Ring of Fire in depths not exceeding tens of kilometres. Earthquakes occurring at a depth of less than 70 km are classified as 'shallow-focus' earthquakes, while those with a focal-depth between 70 and 300 km are commonly termed 'mid-focus' or 'intermediate-depth' earthquakes.
In subduction zones, where older and colder oceanic crust descends beneath another tectonic plate, deep-focus earthquakes may occur at much greater depths (ranging from 300 up to 700 kilometers). These seismically active areas of subduction are known as ‘Benioff zones’
Deep-focus earthquakes occur at a depth at which the subducted lithosphere should no longer be brittle, due to the high temperature and pressure.

30. What is the ‘Benioff zone’? (Ref Hodder p.7)
The BENIOFF ZONE is an area of seismicity corresponding with the slab being thrust downwards in a subduction zone.
The different speeds and movements of rock at this point produce numerous earthquakes.
It is the site of intermediate/ deep-focused earthquakes.
This is an important factor in determining earthquake magnitude since it determines the position and depth of the ‘hypocentre’

31. What is the hypocentre? (Ref : Hodder p.8 see fig 1.10)
This is the ‘focus’ point within the ground where the strain energy of the earthquake stored in the rock is first released.
The distance between this and the epicentre on the surface is called the FOCAL LENGTH
The hypocentre can occur at any depth between the earth’s surface and about 700km.
The most damaging events are usually shallow focus , with a hypocentre of less than 40 km

32. TASK: RESEARCH FAULTS
What is a normal fault?
What is a strike/ slip fault?
What is a thrust/ Megathrust fault and how is it caused?
What is meant by the term a locked fault?
(Ref : Hodder p.7)

33. Faults : Another zone where earthquakes occur
Two sides of the fault slip horizontally past each other ; transform boundaries are a particular type of strike-slip fault
Normal faults occur mainly in areas where the crust is being extended such as a divergent boundary /constructive
Reverse faults occur in areas where the crust is being shortened such as at a convergent boundary/destructive

34. THRUST/MEGATHRUST/FAULTS
Formed at a subduction zone at the point of plate contact. When the plates are locked together, frictional stress builds.
When this stress exceeds a given threshold, a sudden failure occurs along the fault plane that can result in a ‘mega thrust earthquake’ e.g. Japan earthquake and tsunami March 2011
This releases strain energy and radiates seismic waves

35. Diagram to show tectonic activity and cause of ‘mega thrust earthquake’ in Japan

36. LOCKED FAULT
It is common for the leading edge of a megathrust fault to LOCK under high friction. This locked fault may hold for thousands of years, building up enormous strains of energy before releasing.
The process of strain , stress and failure is referred to as the ‘elastic rebound theory’.
A locked fault is therefore one that is not slipping because the frictional resistance on the fault is greater than the shear stress across the fault- so it is stuck.

37. Such faults may store strain for extended periods that is eventually released in a large magnitude earthquake when the frictional resistance is eventually overcome
E.g The 2004 Indian Ocean tsunami was the result of a megathrust locked fault(subducting Indian Plate)with strain energy building per year. It generated huge seismic waves and the devastating tsunami.

38. Diagram to show a tsunami forming as a result of strain energy being released from a locked fault

39. TASK
‘Explain the physical processes which would account for the reasons why some earthquakes are of low and some are of high hazard risk.’ (10 marks) TIPS What is a hazard/hazard risk? Explain: give reasons why Physical processes: detail required at different plate boundaries Include key terms: e.g plate boundary types, subduction, Benioff zone , hypocentre…. Give examples (Ref Hodder p4-9)

40. Human activity can also cause earthquakes e. g
Human activity can also cause earthquakes e.g. FRACKING FOR SHALE GAS (Lancashire UK-2011-present)
So, are humans also responsible for earthquakes?
See ‘The Times ‘ newspaper article ( synoptic angle..)

41. Recap: Where do earthquakes happen
Recap: Where do earthquakes happen? Are they ALL found at plate boundaries?

42. TASK: RESEARCH How are intraplate earthquakes formed?
: The Geological Society)

43. INTRAPLATE EARTHQUAKES
@ 5% of earthquake activity takes place WITHIN a plate, AWAY from a plate boundary…
The causes of intra plate earthquakes is still not fully understood . Some are associated with pre existing weaknesses in plates which can become reactivated.
It is thought that zones of weaknesses occur as plates (pieces of solid lithosphere) move about on a spherical surface. Intra plate earthquakes therefore form along these lines of weaknesses.

44. Whilst intraplate earthquakes are not usually as large as earthquakes found along plate boundaries they can still cause a large amount of damage………………..

45. Intraplate earthquake: Gujarat, NW India 2001

46. Effects of intra plate Gujarat earthquake 2001

47. TASK
Research 5 facts (LITERALLY!) about the Gujarat India earthquake 2001

48. H/W/CW
Make brief notes on the case study of the Market Rasen earthquake, Lincolnshire UK Feb 27th 2008.
Why did it occur if the UK is not on a plate boundary?

49. See H/W Task ( separate yellow sheet)
Mystic Meg 2016?!
‘With the use of examples, describe the characteristics and explain the causes of earthquakes.’

50. TASK: Describe and explain the global distribution of earthquakes
TASK: Describe and explain the global distribution of earthquakes. Which areas are of particularly high risk?

51. PLENARY
Devise 3 factual questions ( with answers) from this lesson and test your neighbour!
5 mins- GO

52. Learn all key terms for a quick points test next lesson
H/W
Learn all key terms for a quick points test next lesson