1. TASK Outline the features of seismic waves.
Explain how they are responsible for different primary and secondary hazards ( 6 marks)
Tips
Explain : Give reasons
Define hazard
Say how each type of wave is different but more importantly how and why each might influence primary and/ or secondary earthquake hazards

2. RESEARCH EXTENSION TASK
Research the significance of P and S waves on giving us indirect evidence for the internal structure of the earth

3. Indirect evidence for the structure of the earth: seismic waves

4. Indirect evidence for structure of the earth: Seismic waves (N
Indirect evidence for structure of the earth: Seismic waves (N.B see later earthquake notes)
Vibrations from large earthquakes are detected as seismic waves by seismographs all around the world.
Analysis of many earthquakes over the last 100 years has helped geologists to build up a detailed picture of the inside of the earth.
P and S waves are seismic waves that travel through the layers of the earth, so are called ‘body waves’.
P waves travel fast and CAN move through solids and liquids
S waves travel more slowly and CANNOT travel through a liquid.

5. The nature of P and S waves
P and S waves travel:
1.Faster if the rock becomes more rigid and more incompressible
2.Slower if the rock becomes more dense.
By studying the nature of P and S waves this has become indirect evidence as to the composition of the earth’s different layers.

6. So, where are P and S waves found exactly?...
P waves, like sound waves, consist of successive compression and stretching of particles in the rocks .
They can therefore be found in the earth’s solid inner core as well as the mantle since they can travel through solids and liquids.
S waves, on the other hand, travel more slowly and are transverse waves, meaning that particle motion is sideways. Since S waves cannot travel through liquids they are not found in the outer core. They are found in the mantle, however.

7. The ‘Shadow zone’
In 1906 Richard Oldham noticed that for large earthquakes, the P and s waves were not recorded by seismographs located within a zone which lay at large distances from the focus( point of earthquake origin) i.e between 103 – 143 degrees. This is called ‘the shadow zone’ (see diagram)

8. To Summarise..
Seismic waves give us information that helps in the understanding of the earth’s interior.
P and S waves travel through the earth from the focus of an earthquake and are recorded on a seismograph.
The velocity of the waves depends on the density and elasticity of the medium through which they pass.
The timing of the waves received on the seismograph has enabled scientists to locate the core of the earth and determine other aspects of its interior….

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

10. Let’s Revisit 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)……

11. Can you give some examples?
WHITEBOARD QUESTONS
What is the difference between a primary/ secondary earthquake effect/ hazard??
Can you give some examples?

12. What is an earthquake effect ?
.A primary effect is any damage caused as a direct result of the seismic waves travelling through the crust.It is immediate eg ground shaking, building and bridge collapse, trapped people, cracking gas pipes
A secondary effect is any damage that results from the primary effects – not the quake itself eg. Fires from gas mains, disease from poor sanitation, traffic grid lock, liquefaction, tsunami

13. Are these primary or secondary effects ?

14. What has happened here?

15. Secondary effect/ hazard: Liquefaction
See ‘Japan quake- incredible liquefaction taking place , ground shifting’

16. What is soil liquefaction? ?
When the ground shakes it causes water in the ground from saturated soils to rise up to the surface (N.B Saturated soils are those in which the pore space between individual particles is completely filled with water)
As it does it turns the ground to ‘jelly like mud’
It often happens where the ground is not solid but infilled. Soils with a high water content lose their mechanical strength ( e.g poorly compacted sand and silt)
As a result the liquified soil may flow and the ground may crack and move.
(See clip on model of liquefaction)

17. See Fig 1.13 Hodder p.10

18. Why is soil liquefaction so hazardous?
Liquefaction can cause buildings to settle, tilt and eventually collapse in the most serious of events.
In some cases tilts of up to 60 degrees have been recorded eg. Japan.
Land adjacent to rivers and sloping ground can present a hazard by sliding under low- friction conditions across a liquefied soil layer. This is called LATERAL SPREADING, sometimes creating large fissures or cracks in the ground surface.

19. Effects of liquefaction…

20. Liquefaction causes considerable damage to surface structures ( e g roads and bridges) and underground and overhead utilities( gas, electricity, sewerage)
Buildings may ‘sink’ as a result
Certain areas are more prone to liquefaction than others e.g. San Fransisco, where development has occurred on reclaimed land thus the area is more vulnerable. Estimated US$ 100,000 mill worth of damage caused in 1989
The short term impact on the delivery of aid and the longer term rebuild costs can be substantial as a direct result of this secondary impact

21. LANDSLIDE: another secondary hazard…

22. What is a landslide and how hazardous are they?
A landslide is the rapid downslope movement of rock or soil. They typically occur in response to a trigger such as a rainstorm or slope failure due to ground shaking in an earthquake which destabilises the hillside and causes it to move downslope. Most problematic in countries that are part of the India-Eurasian plate collision, esp China, Nepal, India and Pakistan.
As many destructive boundaries occur in mountainous areas, landslides( as well as rock falls and avalanches) can be major secondary impacts.

23. LANDSLIDES cont…
Studies linking earthquake INTENSITY to landslides show that they rarely occur when magnitudes are less than 4 but that significant problems occur when they are larger.
Research by the USGS suggests that over the last 40 of all deaths caused by earthquakes globally ( excluding those from shaking, building collapse and tsunami) are attributable to the secondary effects of landslides. E.g. in the 2005 Kashmir, Pakistan and 2008 Sichuan, China earthquakes, landslides accounted third of all deaths

24. Time for an exam question: June 2010 Q1
Time for an exam question: June Q1. Study fig 1, a photo of an area in northern Pakistan after a recent earthquake. Using fig 1 only, comment on the evidence that suggests that an earthquake has recently taken place ( 7 marks)

25. TASK:RESEARCH QUESTION
‘With reference to named examples explain why some locations are more at risk from liquefaction but others from landslides.’ (8 marks)
Tip : Use RECENT examples eg Nepal 2015, Japan 2011,San Francisco 1989, Christchurch New Zealand (any others?)
Explain physical processes. Think about how geology affects them
What human factors make some locations more at risk than others?
Refer to the exam question throughout- emphasis on which locations are more at risk than others and why………….
Refs:
Hodder P.9-10
Oxford P 13-15
READ ARTICLE IN GEOGRAPHY REVIEW MAGAZINE- ‘AFTER THE SHAKING (p.26-27)
Any other source you can find..

26. Nepal Earthquake 7.5 April 25 2015