TOPIC 1:TECTONIC PROCESSES AND HAZARDS (Lesson 8)

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

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

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

4. WHITEBOARD STARTERWhat are the names of the following plate boundary types: • 1.Where two plates move apart from one another? • Divergent/constructive • 2.Where two plates move towards one another and meet? • Convergent/destructive • Where two plates move past each other either in the same or different directions? • Conservative/transform/slipping/transform

5. 4. There are three types of convergence at a destructive plate boundary. Name the types of plates involved in each: • 1. Ocean- continent convergence • 2. Ocean- ocean convergence • 3. Continent- continent convergence ( collision) 5. Volcanoes cannot be found at Conservative or collision plate boundaries 6. An example of a conservative plate boundary is? • San Andreas fault line, California, USA • https://www.youtube.com/watch?v=FIgksa3x11w

6. EARTHQUAKES!!

7. 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- Your Booklet:P.

8. 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)

9. WHITEBOARD Q In pairs discuss what you think an earthquake is exactly?

10. WHAT ARE EARTHQUAKES?( write notes p.) • 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.

11. FASTEST PERSON ON THE BUZZER………! When and where was the largest earthquake ever recorded? • http://geology.com/records/largest-earthquake/ • CHILE May 22 1960- Magnitude 9.5 • See Table 1.1 p.9 Hodder :Largest recorded magnitude earthquakes since 1990

12. Epicentre, focus and seismic waves The focus/hypocentre is the origin of the earthquake below the ground surface and is the point at which the rock moves Seismic waves are ripples of energywhichstart at the focus and cause the ground to move Theepicentreisdirectly above the focus on the earth’s surface. It is where the earthquake is most strongly felt.

13. Draw the diagram below: A Cross section of an earthquake Epicentre seismic waves Focus/hypocentre Fault line

14. Earthquake intro clips • https://www.youtube.com/watch?v=8QNigxTN384 • ( Ian Stewart- the anatomy of an earthquake) • http://www.bbc.co.uk/schools/gcsebitesize/geography/natural_hazards/earthquakes_video.shtml • http://www.bbc.co.uk/learningzone/clips/what-causes-earthquakes/14060.html

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. What causes large earthquakes? • https://www.youtube.com/watch?v=8bOlKZTasxI

18. Where do earthquakes happen?SEE DISTRIBUTION OF EARTHQUAKES IN BOOKLET p.Read/highlight..

19. TASK: Describe and explain the global distribution of earthquakes. ADD THIS QUESTION:Which areas are of particularly high risk?

20. Add these new key terms… • The distribution of earthquake activity reveals the following pattern of tectonic activity: • 1) The ‘OCEAN FRACTURE ZONE’ (OFZ)- a belt of activity through the oceans along the mid- ocean ridges, coming ashore in Africa, the Red Sea, the Dead sea rift and California. • 2) The ‘CONTINENTAL FRACTURE ZONE’(CFZ)- a belt of activity following the mountain ranges from Spain, via the Alps, to the Middle East, the Himalayas to the East Indies and then around the Pacific.

21. BBC Earthquake animation: causes and characteristics of earthquakes • http://news.bbc.co.uk/1/hi/sci/tech/7533950.stm

22. Causes: why do earthquakes happen?P. • 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.

23. 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

24. Which boundaries are these and what is happening?https://www.youtube.com/watch?v=Kg_UBLFUpYQ‘Tectonics of the Planet Earth from @10.11 secs’ earthquakes at destructive plate margins SEE PREVIOUS PPT NOTES and Edexcel New A level Hodder book p4

25. Q:Where do many earthquakes form?A: At all major plate boundaries! Figure showing the tectonic setting of earthquakes

27. Earthquakes form at Conservative Margins

28. 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

29. 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

30. 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

31. *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

32. 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 kilometres). 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.

33. 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 ‘focus or hypocentre’

34. Destructive( convergent) 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 2. Crust Melts in subduction zone and creates a deep ocean trench 3.Friction causes heat which melts ocean crust in to mantle in the BENIOFF ZONE which causes earthquakes

35. 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

36. TASK: RESEARCH FAULTS https://www.youtube.com/watch?v=qQ9Mw_rtDng&feature=player_embedded 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 and Weebly lesson 8 slide 32 onwards)

37. 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

38. THRUST/MEGATHRUST/FAULTS • Thrust/Megathrust fault: • 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

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

40. *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.

41. 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 at @20mm per year. It generated huge seismic waves and the devastating tsunami. https://www.youtube.com/watch?v=FRY3fN-NY30 • http://www.bbc.co.uk/science/earth/natural_disasters/earthquake#p00gfgjj

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

43. CW TASK • 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???????

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

45. TASK: RESEARCHHow are intraplate earthquakes formed? • https://www.geolsoc.org.uk/Plate-Tectonics/Chap3-Plate-Margins/Mid-plate(Ref : The Geological Society) • http://www.ck12.org/earth-science/Intraplate-Earthquakes/lesson/Intraplate-Earthquakes-MS-ES/

46. Minor earthquake occurs in Cornwall Oct 17th 2016 • http://www.bbc.co.uk/news/uk-england-cornwall-37791494

47. 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.

48. Whilst intraplate earthquakes are relatively rare and are not as large as earthquakes found along plate boundaries they can still cause a large amount of damage………………..

49. Intraplate earthquake: Gujarat, NW India 2001

50. Effects of intra plate Gujarat earthquake 2001