3. Earthquakes - can they be managed? Learning Outcomes – by the end of this section, you should be able to • understand the global distribution and causes of earthquakes in relation to plate boundaries; • know and understand that there may be physical consequences of earthquakes: – liquefaction; – tsunami; • know and understand the causes and impacts of earthquakes and evaluate the management responses using two case studies (one in an MEDC and one in an LEDC): – identify the plates involved; – describe the short and long term impacts on people and the environment; – evaluate the management response to earthquakes including o prediction/precautions before the event and o immediate and long term strategies implemented after the event. Key Terms
Dorothy’s dilemma... We make choices everyday. From the moment we get up (what cereal will I have this morning?) right through to the night time (Will I do my Geography
homework or watch the next exciting instalment of Panorama on BBC2 - can’t miss that one, you know!!). From the mundane (what time will I get up on
Saturday) to the important and life shaping (how quickly should I reply to his/her text so that I don’t appear too desperate and too much of a stalker?!?!
Oh, I really fancy him/her but I want to play it cool ... but not so cool that he/she thinks I’m not interested at all. AGGHHH - help!!) But I bet you never have faced Dorothy’s dilemma. One normal day, her day was filled with normal choices, things that she never really thought twice about. Until she was suddenly thrust into an almost unimaginable situation and faced with the most
staggering of choices - should I get my leg cut off without anaesthetic - or should I allow myself to slowly be burned alive?… So what’s the story here? Check out the video of the 1989 Loma Prieta earthquake to see what choice you would make if you were faced with Dorothy’s dilemma…
GCSE Theme C: The Dynamic Earth – Lurgan College Geography Department
3.1 Earthquakes - where and how? What is an earthquake?
How do earthquakes occur?
The focus and the epicentre The focus is
The epicentre is
GCSE Theme C: The Dynamic Earth – Lurgan College Geography Department
Measuring earthquakes Earthquakes are measured using seismographs. These measure the vibrations of the earth’s crust caused by an earthquake. The size (or magnitude) of the quake can be expressed using the Richter Scale (from 1 to 10).
On the graph below, add the magnitudes for the following earthquakes: Dudley, 2002; Loma Prieta 1989; Boxing Day tsunami 2004.
GCSE Theme C: The Dynamic Earth – Lurgan College Geography Department
Location of earthquakes Compare this map of earthquake epicentres with you earlier map of plate boundaries. Complete the following statement: Most major earthquakes occur ________________________________.
GCSE Theme C: The Dynamic Earth – Lurgan College Geography Department
3.2 Physical consequences of earthquakes Learning Outcomes – by the end of this section, you should be able to •
know and understand the following physical consequences of earthquakes: o tsunamis o liquefaction
Key Terms
A. Tsunamis Girl, 10, used geography lesson to save lives A 10-year-old girl saved her family and 100 other tourists from the Asian tsunami because she had learnt about the giant waves in a geography lesson, it has emerged. Tilly Smith, from Oxshott,
Surrey, was holidaying with her parents and seven-year-old sister on Maikhao beach in Phuket,
Thailand, when the tide rushed out.
As the other tourists watched in amazement, the water began to bubble and the boats on the
horizon started to violently bob up and down. Tilly, who had studied tsunamis in a geography class
two weeks earlier, quickly realised they were in danger. She told her mother they had to get off the beach immediately and warned that it could be a tsunami. Her parents alerted the other
holidaymakers and staff at their hotel, which was quickly evacuated. The wave crashed a few minutes later, but no one on the beach was killed or seriously injured. In an interview with the Sun, Tilly gave the credit to her geography teacher, Andrew Kearney, at
Oxshott's Danes Hill Prep School. She said "Last term Mr Kearney taught us about earthquakes and how they can cause tsunamis.”
GCSE Theme C: The Dynamic Earth – Lurgan College Geography Department
http://news.bbc.co.uk/cbbcnews/hi/newsid_4130000/newsid_4137800/4137839.stm Use the animation contained on this webpage and the information in the text box to help you complete the table below. The tsunami behaves very differently in deep water than in shallow water. In deep ocean water, tsunami waves form only a small hump (the maximum height of the 2004 tsunami caused by the earthquake at the margin of the IndoAustralian Plate and the Eurasian Plate was 60cm), barely noticeable and harmless. They generally travel at a very high speed of 300 to 600 mph. However, in shallow water near coastlines, a tsunami slows down to only tens of kilometres an hour. But, as it does so, the height can increase considerably. Scientists investigating the damage in Aceh found evidence that the wave reached a height of 24m when coming ashore along large stretches of the coastline, rising to 30m in some areas when travelling inland. The first warning sign of a possible tsunami is the earthquake itself. However, tsunami can strike thousands of kilometres away where the earthquake is only felt weakly or not at all. Also, in the minutes preceding a tsunami strike, the sea often recedes temporarily from the coast. Around the Indian Ocean, this rare sight reportedly induced people, especially children, to visit the coast to investigate and collect stranded fish on as much as 1.5 miles of exposed beach, with fatal results.
Cause An earthquake along the boundary between the _____________________ and _____________ plates forced the seabed _________. This displaced (moved) ________ of cubic kilometres of water.
Characteristics In deep water…
…at the shore
Wave length Wave height Speed
Consequences See question on next page (note you don’t have to learn these facts – this is not a case study).
GCSE Theme C: The Dynamic Earth – Lurgan College Geography Department
Study figure 1 and 2 which show information about the earthquake in the Indian Ocean on 26 December 2004. Answer the questions which follow. Figure 1 A map of the earthquake affected area
Country
Indonesia
Malaysia
Sri Lanka
India
Thailand
Deaths
130,736
68
21,411
12,405
5,394
Figure 2 The deaths resulting from the earthquake in some of the affected countries
(i) Giving a reason for your choice, state the type of plate margin shown in the diagram. __________________________________________________________________________________ _______________________________________________________________________________ (2) (ii) State fully two reasons why the death totals in Indonesia were so high compared with other countries. In this question, you’ve got to go looking for evidence from the map, trying to identify reasons. Look at all the information given for clues. Look at the key, see what information has been included. Look at the map – look especially at Indonesia’s location. What ideas can you come up with?
Reason 1 __________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ _______________________________________________________________________________ (3) Reason 2 __________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ _______________________________________________________________________________ (3)
GCSE Theme C: The Dynamic Earth – Lurgan College Geography Department
B. Liquefaction What happened here? What do you notice as unusual in this photo?
GCSE Theme C: The Dynamic Earth – Lurgan College Geography Department
Liquefaction is a phenomenon in which the strength and stiffness of a soil is reduced by earthquake shaking or other rapid loading. In areas where the ground is made of soil rather than rock, the shockwaves sent out by an earthquake causes the grains to lose contact with each other. Instead, they are surrounded by water, causing the soil to flow more like a viscous liquid. You can demonstrate this process to yourself next time your go the beach. Stand on the sand just after an incoming wave has passed. The sand will easily support your weight and you will not sink very deeply into the sand if you stand still. But, if you start to shake your body while standing on this wet sand, you will notice that the sand begins to flow as a result of liquefaction, and your feet will sink deeper into the sand. After the shaking, as the soil water pressure falls again, the ground solidifies once more.
Before the shaking ________________ between grains holds sediment together so ground is solid During the shaking • Grains lose ___________ with other grains and instead are completely surrounded by __________ • Ground begins to act like a ________________ • Anything built on liquefied soil will tend to collapse. After the shaking • water pressure _______ • ground become ___________ again
Liquefaction can have devastating impacts on buildings. This photo shows a building that experienced liquefaction during the 1989 Loma Prieta earthquake. • What evidence is there here that liquefaction has occurred? • What would it have been like to have been inside the building when this happened? o What would you have seen? o How would you have felt? o What would you have done?
GCSE Theme C: The Dynamic Earth – Lurgan College Geography Department
3.3 Earthquakes - causes, impacts & management response As we have already seen, earthquakes can cause horrendous loss of life and livelihood for people who live in areas stuck by major earthquake events. We’re about to look at two case studies of specific earthquakes, their impacts and the attempts people have made to deal with the earthquake hazard. Before we get in to the case studies themselves, however, we’re going to take some time to brain storm potential factors that influence the extent to which people are affected by earthquakes. Once we’re done with the case studies, we’ll come back to this and see if there are any more factors we can add.
GCSE Theme C: The Dynamic Earth – Lurgan College Geography Department
Loma Prieta, 1989 An earthquake in the USA (an MEDC)
A. Cause
•
Using your previous map of plate boundaries, name the two plates involved in this earthquake. Add their names to the map above too.
•
Use the information in the diagram to the right to help you complete the following:
The last major earthquake (over 7.0 on the Richter Scale) prior to 1989 was in _____________ (measuring ____ ). Since then, the ________________________ & _____________________ plates moved in different directions. But ___________ at the plate margin resulted in a build up of _____________, which caused the plates to slowly ___________. Then, in October 1989, all the pressure was suddenly released in a massive __.9 earthquake whose epicentre was at _________________.
GCSE Theme C: The Dynamic Earth – Lurgan College Geography Department
B. Impacts The specification asks us to examine the short and longer term impacts on people and the environment. Being able to understand what is meant by terms and then being able to classify things under these terms is an important skill to work on for your exam. Classify the impacts then add them to your notes in the table below.
Short term impacts On people
Long term impacts On people
On the environment
On the environment
GCSE Theme C: The Dynamic Earth – Lurgan College Geography Department
Short term impacts Firstly, the impacts on people. Altogether, there were 66 deaths and 3,757 injuries as a result of this earthquake. The highest concentration of fatalities, 42, occurred due to the collapse of the Cypress overpass. In addition, over 12,000 lost their homes. Shaking of the ground caused a number of buildings to collapse, especially the older buildings in the Bay area which were built on unstable clays.
Secondly, the impact on the environment. There were landslides in the surrounding rural areas, eg the Santa Cruz mountains, where a number of roads were closed. Liquefaction occurred in the central San Francisco Bay Area (eg Treasure Island) on land reclaimed from the sea. These sites typically had 10 to 30 feet of loose, sandy fill. The extent of liquefaction and its consequences were limited, however, due to the short duration of strong shaking in this earthquake (8 to 10 seconds). Long term impacts The main long term impacts on people were as follows: over 10,000 people lost their jobs as roughly 4000 businesses were totally destroyed. The cost of the repairs came to over $7 billion. As far as the built environment was concerned, the Bay Bridge re-opened within one month, but the work needed to protect it from another big ‘quake didn’t start until 2002 and isn’t due for completion until 2011. The Cypress overpass had to be demolished, and it took until 1997 until a (single storey!) replacement was completed.
GCSE Theme C: The Dynamic Earth – Lurgan College Geography Department
C. Management Response i. Predicting earthquakes Although California is heavily monitored by seismographs, it is not currently possible to predict when an earthquake will occur. All scientists have been able to do is give the probabilities of an earthquake occurring in a certain area. For example, there is a ___% probability of a major earthquake in the Bay area of San Francisco in the next ______ years! Not much use for knowing when to order an evacuation!
ii. Precautions before the event Much more can be done in this area to try to reduce the impacts of earthquakes. •
Preparing people A lot has been done to prepare the people of California for earthquakes. For example, starting in 2008, California has had a state wide earthquake drill called the Great California Shake Out. Visit this website (www.shakeout.org) and make some notes on what happens during the drill. Include things like the numbers of people who took part and the main advice that is given about what to do during a quake.
This is a Health and Safety Officer from a Californian university, setting a good example of how to prepare for an earthquake. What precautions has he taken? • Preparing buildings Following earlier earthquakes, a number of the modern skyscrapers in San Francisco have been designed to be more earthquake resistant. For example, the occupants of the Transamerica Pyramid were unnerved as the top floor of the skyscraper swayed more than 1 foot from side to side for more than a minute during the 1989 ‘quake. However, rubber shockabsorbers placed in the foundations, allowed the building to flex with the shaking, and reduced the shake forces by 25%.
GCSE Theme C: The Dynamic Earth – Lurgan College Geography Department
iii. Strategies adopted after the event In the immediate aftermath of the earthquake, emergency services were dispatched to rescue survivors. These included the fire service who attended the collapsed Cypress overpass and who managed to extract Dorothy Otto from her trapped car using the jaws of life. Other officials and police searched buildings for survivors. In the longer term, there were improvements to some of the structures damaged during the quake. For example, the Bay Bridge re-opened within one month, and the work needed to protect it from another big earthquake started in 2002 and is due for completion by 2011. In addition, following the 1989 earthquake, the seismometers (which would have given vital information about the location of the epicentre) had their power source cut off. Since then, many have been updated to have their own emergency generators so that they can keep working after any future earthquake.
GCSE Theme C: The Dynamic Earth – Lurgan College Geography Department
An earthquake in an LEDC
A. Causes
B. Impacts Short term impacts On people
Long term impacts On people
On the environment
On the environment
GCSE Theme C: The Dynamic Earth – Lurgan College Geography Department
C. Management Response (i) Predictions/precautions before the event
(ii) Strategies implemented after the earthquake
GCSE Theme C: The Dynamic Earth – Lurgan College Geography Department
Earthquake risk assessment Location: ______________________________________________ Risk
Precautions taken to reduce or manage risk
Procedures to follow in the event of an incident
Assessment Prepared by: _________________________________ Date: _____________________________
Reflecting on the exercise 1. If we followed all your advice on improving safety, how much of a difference would it make to the hazard potential of the room if a Loma Prieta sized earthquake were to strike?
2. The point of exercises like this in California is to make people more aware of the specific risks associated with earthquakes before one strikes so that, during and after a major quake, they know more instinctively what to do. What impact do you think exercises like this actually make to people during an earthquake?
3. Why might making these improvements be more challenging in an LEDC? Explain your answer. (Clue: what is one of the main differences between an MEDC and LEDC?)
4. How would you complete the following sentence?
Similar sized earthquakes tend to cause more damage in LEDCs because‌
GCSE Theme C: The Dynamic Earth – Lurgan College Geography Department
Death toll
Study the table and the graph which show a selection of earthquakes from some MEDCs and LEDCs including the size of and number of deaths caused by the earthquake. • Classify the countries as MEDC or LEDCs on both the table and graph. • To what extent do you agree with the following statement: As the magnitude of the earthquake increases, the numbers of deaths caused increases.
Magnitude
We’ve already seen from our two case studies that the loss of life resulting from the Loma Prieta 1989 earthquake was much lower than that of the ___________________________ earthquake. Let’s take a slightly broader look to compare a series of earthquake in MEDCs and LEDCs to see if that is a general pattern between all MEDCs and all LEDCs.
Location
Differences in earthquakes between MEDCs & LEDCs
Java
6.3
5,800
Bam-Iran
6.6
27,000
NorthridgeLos Angeles, USA
6.7
60
ChuetsuJapan
6.9
39
Kobe, Japan
7.2
6,400
KashmirPakistan
7.6
87,000
Gujarat-India
7.9
30,000
TangshanChina
8.2
242,000
Indian Ocean
9.2
229,000
9.5
300,000
9 250,000 8.5 8
200,000
7.5 150,000 7 6.5
100,000
6 50,000 5.5
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GCSE Theme C: The Dynamic Earth – Lurgan College Geography Department Death toll
Why is this the case? Why do earthquakes cause more damage in LEDCs than MEDCs? Use your understanding of your case studies and the extract below to help you answer the question below. On 17 October 1989, an earthquake measuring 7.1 on the Richter scale rocked the United States city of San Francisco. The Loma Prieta earthquake, as it became known, killed 68 people and brought more than 24,000 homes crashing down. This was certainly a disaster, but a relatively minor one compared to what hit Izmit, Turkey on 17 August 1999. That earthquake, registering 7.4 on the Richter scale, took the lives of at least 17,100 people and flattened 300,000 homes. Why would two earthquakes of similar magnitude have such different impacts? Timing had something to do with the difference in casualties – the San Francisco earthquake occurred in the afternoon, when relatively few people were at home. In Izmit, many people were sleeping and could not escape their collapsing apartments. But the main reason was that San Francisco was more prepared. In San Francisco, most houses, offices, sports stadiums, roads and bridges had been built to resist earthquakes, and emergency services were ready to lend assistance throughout the city. In Izmit, many buildings had been poorly constructed, and it was mostly these that collapsed. There was no real emergency plan: thousands of people made homeless by the quake had nowhere to go and little access to medical services. Diseases such as typhoid and hepatitis quickly became killers. The lessons from these two examples are clear: long-term planning can greatly reduce the impact of earthquakes, and it is most needed in developing countries. Adapted from: www.science.org.au/nova/088/088key.htm
“Earthquakes don’t kill people - buildings do.” Do you agree? Explain your answer. (HINT: take a ‘to what extent’ approach with this question) ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ GCSE Theme C: The Dynamic Earth – Lurgan College Geography Department
Handling case study questions Case study questions are common in the exam. But how do you score well in them? What is the examiner looking for in a successful case study exam answer? Take a look at this past paper question and the mark scheme to help you come to answer these questions. (e) Name an earthquake you have studied. (i) Explain the cause of the earthquake. (ii) State fully two strategies put in place after the event to reduce loss of life in future earthquakes. Earthquake _______________________________________________ (i) Cause ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ _____________________________________________________________________________ (3) MARK SCHEME Cause Level 1 (1) A simple stated cause e.g.
•
Notes
• The earthquake in Japan was caused by plate movement.
Level 2 (2) A cause stated with some explanatory detail e.g.
• The earthquake in Japan was caused by movement along a
complicated destructive plate boundary/one plate goes under the other. Level 3 (3) A cause stated with good detail – including one fact or figure, e.g. plates named
• Kobe, in Japan , January 1995. This earthquake was caused by
movement along a plate boundary where the Pacific, Eurasian and
Philipine plates meet. This particular earthquake was caused by the
subduction of the Philippine plate beneath the Eurasian plate. Although this averages 10 cm per year, friction had stopped the smooth
movement of these plates for some time, until the pressure to move was
so great that they shunted and moved just over 2 m horizontally in the space of 20 seconds. This created shockwaves felt on the earth’s surface as an earthquake.
GCSE Theme C: The Dynamic Earth – Lurgan College Geography Department
(ii) Strategies ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ ________________________________________________________________________________ _____________________________________________________________________________ (6)
Two strategies (2 x 3 marks) Level 1 (1) Only one strategy noted – with a low standard of detail e.g. • After the event new building codes were introduced.
Notes
Level 2 (2) Two strategies covered fairly well or one strategy covered well • Buildings were strengthened after the earthquake. This meant that in future
events they would absorb the shockwaves rather than falling down. This would reduce the overall damage caused by another strong earthquake in a MEDC.
Level 3 (3) A top level answer which addresses two strategies in detail. One fact included for each strategy. • After the quake new building codes were introduced that meant high rise
buildings had to have flexible frames. This meant that they would sway rather than collapse. This would reduce the number of buildings that would collapse, reducing the deaths, as buildings tend to be a major cause of deaths in earthquakes.
•
Following this the government invested money to build several 100 000 litre water cisterns to supply clean water, and bought 11 bulk water supply
units for the ground fleet of the fire service and new wider (100 mm) hoses for the fire ships, so that large quantities of water could be
dispatched by the fire brigade in any future quakes, thus reducing damage caused by out-of-control fires.
GCSE Theme C: The Dynamic Earth – Lurgan College Geography Department
When you see three, use SCE! One very common type of exam question is the three mark question we’ll call the SCE question. There is a particular way you need to answer it, and we’re going to look at it now to teach you how to be successful with it in the exam.
1. Spotting SCE questions There are two clues: • The question will be worth three marks (or six marks but with two parts) • The command phrase may be ‘State fully one’
2. What is SCE? Let’s use this SCE question as a worked example.
Using evidence from the figure, state fully one reason why there were more deaths in Bourmerdes than Algiers. (3)
What does SCE stand for? Statement
What do these words mean? What is the main point of your answer?
Consequence
So what?!?
Elaboration
Tell me more!
Example of an answer
GCSE Theme C: The Dynamic Earth – Lurgan College Geography Department
2. Have a go Try completing this alternative answer to the above question:
S = There are fewer deaths in Algiers because it is the capital city. C=
E=
3. Common SCE errors What’s wrong with these answers?
S = There are more deaths in Boumerdes because it is closer to the epicentre. C = Therefore the shaking will be more severe here. E = Also, Boumerdes is not the capital city so there may not be as many rescue services here.
S = There are more deaths in Boumerdes because it is closer to the epicentre. C = Therefore the shaking will be more severe here. E = That’s why there are more deaths there.
4. Now practice some more (i) Earthquakes in LEDCs often result in more loss of life than earthquakes in LEDCs. State fully one reason why this is so. (3) __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ __________________________________________________________________________________ _______________________________________________________________________________ (3)
GCSE Theme C: The Dynamic Earth – Lurgan College Geography Department