TOPIC 1:TECTONIC PROCESSES AND HAZARDS (Lesson 9)

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?

PREVIOUS 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

WHITEBOARD STARTER QS

Recap: 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)

Today’s lesson objective Specification 1.3a) To explain how earthquake waves (P,S and L waves) cause crustal fracturing , ground shaking and secondary hazards(liquefaction and landslides) Ref: Hodder p8-11

SEISMICITY: EARTHQUAKES: SEISMIC WAVES

WHAT IS A SEISMIC WAVE AND HOW IS IT FORMED?? RECAP Q: WHAT IS A SEISMIC WAVE AND HOW IS IT FORMED??

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.

S (Secondary/Shear) Wave Types of Seismic Waves P (Primary/Push) Wave S (Secondary/Shear) Wave L (Love) Wave R (Rayleigh) Wave

Measuring Earthquakes - Seismometer

Types of Seismic Waves as recorded on a seismogram P & S are Body Waves which travel through the earth L & R are Surface Waves with the largest amplitude, travel around the surface of the earth and cause most damage

SEISMIC WAVES Seismic waves are waves of energy which ripple out from the focus rather like ripples in water when a rock is thrown into a pond. There are three types of seismic waves, each travelling at different speeds: 1)Primary (P) waves: These travel fastest, moving through solids and liquids, through the body of the earth. They are compressional, vibrating in the direction they are travelling. They cause rock particles to compress and dilate, pushing them apart and then back together, shaking the earth backwards and forwards.

p wave animation

http://www.bbc.co.uk/schools/gcsebitesize/science/21c/earth_universe/seismic_wavesrev1.shtml http://www.classzone.com/books/earth_science/terc/content/visualizations/es1002/es1002page01.cfm

DO THE SLINKY EXPERIMENT!

SECONDARY(S)WAVES 2. Secondary(S) waves: Travel at half the speed of P waves through the body of the earth. They vibrate at right angles to the direction of travel. They shake the earth up and down, shearing rock at the same time. They cannot travel through liquids but do more damage than P waves N.B ONE EARTHQUAKE CAN CAUSE BOTH P AND S WAVES!

S WAVES s wave animation (click) Attach one slinky to the centre and at right angles to another and see how P waves can set off S waves!

Locating the Epicentre of an Earthquake Gap between first P and S arrivals is 61 seconds 61 second gap gives distance of 617km to the epicentre Gulf of Mexico 10th September 2006 30 seconds Need to find the time difference between the arrival of the first P wave and the first S wave

SURFACE WAVES 3.Surface waves: When S waves reach the surface they radiate out from the epicentre travelling along the surface to form surface waves These are the slowest moving seismic waves and they move slowly near to the land surface. Since they rock the foundations of man made structures they are, however the MOST DESTRUCTIVE!

TYPES OF SURFACE WAVES: LOVE WAVES!(L WAVES) AND RALEIGH WAVES LOVE(L) WAVES cause the ground to move sideways RALEIGH WAVES have a rolling motion making the earth move up and down Surface waves are transmitted at the earth’s surface much like a water wave on the sea surface and cause the most damage to life and property

raleigh wave animation love wave animation

Love and Raleigh surface waves

Effect of different seismic waves on a seismogram

Remember…. http://www.youtube.com/watch?v=8bOlKZTasxI Seismic waves are the result of stress and strain NOT the cause of an earthquake! Seismic waves are waves that are as a result of earthquake activity in the earth. P S & L waves occur when: The energy radiates outward from the fault in all directions in the form of seismic waves like ripples on a pond. The seismic waves cause crustal fracturing as they move through the earth and when the waves reach the earth’s surface, they shake the ground and anything on it, like our houses and us. http://www.youtube.com/watch?v=P53OJd_lxew http://www.youtube.com/watch?v=8bOlKZTasxI