The causes and effects of earthquakes and how people respond to them


Lesson 1: The structure of the earth

 

Learning objectives:

To know the structure of the earth – inner core, outer core, mantle and crust.
To be able to give the characteristics of each of these layers of the earth.

 

This unit builds on the work that you have done in your science lessons – please revise the work you have done on plate tectonics in science alongside the work you have done in geography. The two subjects complement each other well!

 

You need to know some basic information about the structure of the earth. The earth has four layers – inner core (at the centre), outer core, mantle and crust (see diagram below). Each of these layers has different characteristics.

 

 

The core extends to about half of the radius of the Earth. It is made mostly from iron and nickel and is where the Earth’s magnetic field comes from. It is very dense. The temperature is high and the outer core is molten. Towards the centre high pressure makes the inner core solid. Intense heat is generated in the inner core by decay of radioactive elements like uranium.

 

The mantle extends outwards from the core to the crust: a distance of about 2,900 km. It is mostly a semi-molten liquid upon which the Earth’s crust floats. The heat coming from the core generates convection currents in the viscous mantle that cause the crust above to move.

 

The crust is the thin layer of rock at the surface upon which we live. Eight elements make up over 98% of the Earth’s crust – although they are virtually entirely in the form of compounds.

 

Thanks to the pupils at Maghull High School in Liverpool who made this great little model and video clip to describe the structure of the earth:

 

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Can you work out which layer of the earth each of these statements refers to?

 

I am dense, very hot, made mostly of solid iron and nickel.

I’m iron and nickel too, but I’m liquid.

I’m really very thin and am mostly silicon, oxygen and aluminium

I’m a viscous semi-solid with convection currents circulating in me.

I just hang around on the outside.

 

Useful links:

The earth is like a great big grapefruit song
YouTube clip about the structure of the earth
BBC Interactive KS3 lesson about the structure of the earth - really good for revising key points

 

Lesson 2: Plate tectonics and the theory of continental drift

 

Learning objectives:

To know that the earth’s crust is divided into tectonic plates.

To be able to name some of these plates.

To be able to explain the theory of continental drift.

 

The earth’s crust is made of about twelve plates. These are like big rafts floating on the semi-molten mantle. Convection currents within the mantle cause the plates to move. Although they only move about 2 cm per year, this can have huge effects over long periods of time. The map below shows the distribution of the world’s tectonic plates. Make sure that you can name and locate at least 4 of the plates on a world map.

 

 

Scientists think the continents were originally all together in a super-continent called Pangaea. Over millions of years they have drifted to their present positions on the floating tectonic plates. This movement is shown in the video clips below.

 

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The theory of continental drift is supported by several pieces of evidence. For example, consider the continents of Africa and South America:

 

 

Have a look at the cartoon below? Why might a geologist find this funny?

 

Useful links:

Youtube video clip about the tectonic plates

 

Lesson 3: Where on earth do we find earthquakes and volcanoes?

 

Learning objectives:

To recap the use of latitude and longitude to describe location.

To describe the global distribution of earthquakes and volcanoes.

To know that earthquakes and volcanoes are found at plate boundaries.

 

The examiner expects you to be able to use latitude and longitude to give and find locations and this is an obvious question for you to be asked for this part of the course. Make sure that you are confident in using latitude and longitude – if you are struggling with this, please work through the links below and if you still aren’t quite sure how they work then see your geography teacher straight away for more help. Just sitting there and worrying about it without seeking help will not solve the problem!

 

 

    

 

Longitude lines run north-south and lines of latitude run east-west. The key thing that catches people out is that if you start at 0 degrees longitude and move west, the numbers increase the further you go. Once you’ve realised this, you can just treat the grid of lines as you would the grid on a standard OS map. The video below is really helpful in revising how to use latitude and longitude.

 

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Look at the map below. It shows recent volcanoes and earthquakes. Volcanoes are shown in blue, earthquakes in red. Are they scattered randomly, or is there some kind of pattern? If so, can you explain why?

 

 

You should have realised that volcanoes and earthquakes occur at plate boundaries (where the tectonic plates meet).

 

Earthquakes occur at all plate boundaries irrespective of which direction the plates are moving in.

Volcanoes tend to occur where oceanic and continental plates are moving towards each other or where two oceanic plates are moving apart (where they form mid-ocean ridges). In the next lesson, you will learn more about what happens at these different kinds of plate boundary.

 

You could use the card sort below to help you revise this lesson. Shade the cards that are about the world pattern of earthquakes and volcanoes in red. Then shade those that are about tectonic plates and active zones in blue. Choose a red card. Find a blue card that can be linked with it. Keep going until you have matched all of the statements.

 

 

 

Just in case you got stuck, here are the answers:

 

Active zones are found around the edges of many of the world’s tectonic plates.
Earthquakes and volcanoes occur in linear patterns in some parts of the world.

 

In places, the North American and Pacific Plates are moving past each other.
Volcanoes and earthquakes occur along the west coast of North America.

 

Many volcanoes and earthquakes are clustered together on islands and continents around the edge of the Pacific Ocean.
Around the edge of the Pacific plate is an active zone called the ‘ring of fire’.

 

The  North American and Eurasian plates are moving away from one another.
Volcanoes can be found in a line running north to south down the middle of the Atlantic Ocean.

 

Australia is found in the middle of the Indo-Australian plate.
Volcanoes and earthquakes are not found in Australia.

 

The east coasts of North and South America are not close to active zones.
There are no volcanoes or earthquakes on the east coast of North or South America.

 

There is an active zone where the Nazca and South American plates move together.
A belt of volcanoes and earthquakes is located along the west coast of South America.

 

The Eurasian and Indo-Australian plates are moving towards each other.
Many earthquakes happen in the Himalayan mountains to the north of India.

 

Useful links:

Latitude and Longitude quiz

 

 

Lesson 4: What happens at plate boundaries? 

Learning objectives:

To know what happens at constructive, destructive, conservative and collision plate boundaries.
To be able to draw annotated diagrams to show what happens at each type of plate boundary.
To be able to link the type of plate boundary to the type of hazard found.

Constructive plate boundaries 

To help you remember what happens at constructive plate boundaries, think about Bob the Builder! He works in the construction industry – construction is about making things. So, at a constructive boundary, new land is being made.

 

 

The new land is being made because the plates are moving apart. Magma rises to fill the gap, creating new land. Eruptions here are generally quite gentle as the lava can escape easily. Have a look at the PowerPoint below to see exactly what happens at a constructive plate boundary then try to add annotations to the diagram to explain what is happening. The PowerPoint was written by pupils at Bury Church of England High School. Thanks to them and their teacher, Miss Sumner, for sharing via Slideshare!

        

Those of you who went on the fieldtrip to Iceland saw a constructive plate boundary in the Pingvellir National Park. 

We get both earthquakes and volcanoes at constructive plate margins.

 

 

 

Destructive plate boundaries

  

The earth’s crust gets destroyed at a destructive plate boundary. This happens when an oceanic plate is subducted beneath a continental plate. Oceanic crust is made of basalt whereas continental crust is made of granite. The oceanic crust is thinner than the continental crust but it is heavier, so it is pulled down (subducted). It is destroyed in this way. The crust is turned into magma, which may erupt through a volcano at the plate boundary and become lava.

 

Have a look at the subduction factory cartoon below to see  what happens at a destructive plate boundary, then try to add annotations to the diagram to explain the process.

 

     

 

The Cascades Mountain range on the west coast of the USA lie along a destructive plate boundary. This is where Mount St Helens is located. We get both earthquakes and volcanoes at destructive plate margins.

 

Conservative plate boundaries

  

Conservative plate boundaries occur where plates move side by side. They might move in opposite directions but it could also be that they move in the same direction but at different speeds. The San Andreas fault in California is a good example of a conservative plate boundary. The area has experienced a huge number of earthquakes over the years as this is a very active area.

 

The PowerPoint below explains what happens at a conservative plate margin. Thanks to Jordan Allen for sharing this. Can you add annotations to the diagram to show what happens at this kind of plate boundary?

 

     

 

Collision boundaries

  

The exam board don’t seem to require you to know about this type of plate boundary, but in the interests of making you well-informed geographers, I think you should learn this one too!

 

At a collision boundary, two continental plates move together. The collision forces them upwards forming mountains. This kind of plate movement has caused the Himalayan mountain range to form. We get earthquakes at collision boundaries, but not volcanoes. This is because the two plates are rising upwards rather than being subducted and melting to form magma.

 

Thanks (again) to Miss Sumner and the pupils of Bury Church of England High School for this PowerPoint about collision boundaries:

 

 

To summarise...

  

Constructive – plates move apart forming new land – earthquakes and volcanoes
Destructive – oceanic plate subducted under continental plate – earthquakes and volcanoes (most violent volcanoes are found here)
Conservative – plates move side by side – earthquakes
Collision – two continental plates move together and are forced upwards – earthquakes

 

Watch the first video clip (thanks to cheergalsal) for a really clear summary of the four boundaries then have a go at Kung Fu tectonics (thanks to Adam Brewer). The dance moves are as follows:

 

Constructive boundary – put your hands together above your head; pull them apart; put your head up through the gap

Destructive boundary – make a fist and grasp it with the other hand; slide to your elbow; shake your arms; open your fist and throw it upwards

Conservative boundary – stretch your arms out; rub your palms together and open them rapidly

Collision boundary – smack your first into your palm; push both hands up to form mountains

 

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Useful links:

Plate boundaries fling the teacher revision game
Plate boundaries anagrams game
Plate boundaries quick quiz

 

Lesson 5: What happens in an earthquake?

 

Learning objectives:

To be able to define the terms earthquake, seismic wave, seismometer, focus, epicentre, friction, aftershock.

To know that the Richter scale is used to measure the magnitude of energy released and that the Mercalli scale is used to measure the amount of damage caused by an earthquake.

 

You need to know the following definitions. You could do this match-up quiz to check that you understand the key words.

 

Earthquake – A sudden movement within the earth’s surface, usually close to a plate boundary.

Magnitude – The amount of energy that is given out during an earthquake.

Focus – This is the point underground where the earth’s plates have moved.

Epicentre – The point on the surface directly above the focus.

Seismic waves – These are waves of force that travel through the earth. There are two main types of wave, P waves and S waves. P waves are faster and can travel through solids and liquids whereas S waves are slower and can only travel through solids.

Seismometer –An instrument used to measure the movement of the earth’s surface. A seismometer records the vibrations from earthquakes. Mechanical versions work by way of a large mass, freely suspended.

Click here for an excellent animation showing how a seismometer works.

Seismograph – A graph produced by data collected from the seismometer. This shows the shaking of the earth.

Aftershocks – Aftershocks are smaller earthquakes formed as the crust around the displaced fault adjusts to the effects of the main shock. If an aftershock is bigger than 5.9 on the Richter scale then it is classed as an earthquake.

 

Some of these key features are labelled on the diagram below:

 

 

Earthquakes are sudden ground movements which result from the sudden release of built up energy. This energy is released in the form of seismic waves. Earthquakes are caused due to tectonic movements in the earth's crust. Earthquakes are found at all four of the major plate boundaries (constructive, destructive, collision and conservative boundaries), due to the forces of collision between plates as well as the irregular movement and build up of friction as plates move past each other. Earthquakes also occur away from plate boundaries at weaknesses in the earth's crust known as faults.

As plates move past each other, friction between them results in the build up of pressure. As the plates continue to move and the pressure builds up, eventually the pressure is great enough to overcome friction and the plate jolts forward releasing the pent up energy in the form of seismic waves. The point at the rocks break apart and shock waves start is known as the focus of the earthquake. The point on the surface directly above the focus is known as the epicentre of the earthquake. For further explanation of how earthquakes occur, see this excellent animation from the BBC.

 

These two videos explain what happens in an earthquake:

 

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The Richter scale measures the strength or magnitude (amount of energy released) of an earthquake. The scale is shown below. It is a logarithmic scale and therefore each point on the scale is 10 times greater than the previous one. An earthquake measuring 6 on the Richter scale is therefore 10 times more powerful than an earthquake measuring 5 on the Richter scale.

 

Richter magnitudeDescriptionEarthquake effectsFrequency of occurrence
Less than 2.0 Micro Microearthquakes, not felt. About 8,000 per day
2.0-2.9 Minor Generally not felt, but recorded. About 1,000 per day
3.0-3.9 Often felt, but rarely causes damage. 49,000 per year (est.)
4.0-4.9 Light Noticeable shaking of indoor items, rattling noises. Significant damage unlikely. 6,200 per year (est.)
5.0-5.9 Moderate Can cause major damage to poorly constructed buildings over small regions. At most slight damage to well-designed buildings. 800 per year
6.0-6.9 Strong Can be destructive in areas up to about 160 kilometres (100 mi) across in populated areas. 120 per year
7.0-7.9 Major Can cause serious damage over larger areas. 18 per year
8.0-8.9 Great Can cause serious damage in areas several hundred miles across. 1 per year
9.0-9.9 Devastating in areas several thousand miles across.
1 per 20 years
10.0+ Epic Never recorded; see below for equivalent seismic energy yield.
Extremely rare (Unknown)

  

By contrast, the Mercalli scale was developed in the twentieth century to rate earthquakes according to their intensity. The Mercalli scale ratings are shown below.

 



 

Useful links:

USGS webpage about the Richter scale

Earthquake animation

BBC video clip about what happens in an earthquake - this is really good

 

Lesson 6: Primary and secondary effects of earthquakes

 

Learning objectives:

To be able to explain the difference between the primary and secondary effects of earthquakes.

To be able to give at least three primary effects of earthquakes and at least three secondary effects.

 

The effects of natural disasters such as earthquakes are often classified as primary and secondary impacts.

 

Primary effects of earthquakes happen straight away and occur as a direct result of the ground shaking. For example, shaking of the ground causing buildings to collapse; signs falling off walls; windows shattering; roads cracking; bridges toppling over.

 

Secondary effects occur as a result of the primary effects, and they happen later. For example, fires caused by ruptured gas mains; disease caused by dead bodies that aren’t buried; sewerage pipes bursting and contaminating water supplies leading to death; liquefaction (explained below) causing buildings to collapse. Most of the damage done by earthquakes is from their secondary effects.

 

Liquefaction happens because soft sediment often behaves like quicksand during an earthquake. This is because the shaking brings water to the surface. Buildings often topple over or sink into the ground as a result of this. The Mexico City earthquake of 1985 was so bad because the city is built on old lake sediments and these had the effect of amplifying the shock waves. The diagrams below show how liquefaction operates.

 

 

Now is a good time to review whether you have understood and remembered all of the geographical vocabulary that has been used so far in this unit. This PowerPoint from Bury Church of England High School is a great way to revise the key words. Try to work out which of the terms on the slide matches with the defintiion across the middle of the screen. Make a note of any that you find difficult and keep coming back to review them.

 

 

Useful links:

BBC earthquake guide

USGS earthquakes puzzles and games

Today in earthquake history - find out whether any major earthquakes occurred on today's date in history

USGS information about latest quakes

Earthquake facts from the USGS

Earthquake animations to describe key terms

Careers information about becoming a geophysicist

An explanation of how scientists use seismographs to locate the epicentre of an earthquake

 

Lesson 7: The Kashmir Quake, October 2005 (an LEDC case study)

 

Learning objectives:

To be able to locate the Kashmir region on a map.

To be able to explain why the Kashmir Quake happened.

To be able to give at least 3 primary and 3 secondary effects of the Kashmir Quake.

 

What happened?

  

The area shown on the map was devastated by an earthquake measuring 7.6 on the Richter scale.  The epicentre (the point where the tremors were most severe) was close to the city of Muzaffarabad, the regional capital. This is a densely populated urban area which meant that the amount of damage caused by the earthquake was particularly high.

 

    

 

Why did the earthquake happen?

  

Kashmir lies close to the boundary of two of the giant tectonic plates which form the earth’s crust.  These are moving constantly but very slowly, powered by convection currents in the hot rocks of the mantle immediately beneath the crust. 

 

 

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Who was affected? 

  

The government of Pakistan put the death toll at 55,000 with a further 80,000 injured but these figures are probably an underestimate.  In Muzaffarabad alone, 75% of the buildings collapsed and most of the casualties came as a result of people being crushed beneath the rubble of their homes, schools or workplaces.  In rural areas, where traditional stone or mud brick houses offered little resistance to the violent shaking of the ground, entire villages were destroyed leaving no-one alive.  The earthquake caused landslides in the mountainous countryside which destroyed roads and isolated farms.  It is probable that the bodies of some victims will never be found, lying as they do beneath thousands of tonnes of rock and soil.  Electricity and telephone lines were brought down leaving survivors without power or any means of communicating with the outside world.  Roads outside the towns in Kashmir are little more than narrow dusty tracks at the best of times, but with many of them blocked by landslides it was almost impossible for emergency services to reach casualties or for survivors to travel to the larger towns where medical help and emergency food and water might be available.  The towns and cities faced problems of their own.  Water and sewage pipes broke leaving people without water supplies and allowing domestic and industrial waste to flood the streets.  There are fears that the people will be forced to drink contaminated water resulting in further deaths from diseases like cholera.  Kashmir is in the foothills of the Himalayas where heavy snow falls from the middle of November through to April.  With their homes and crops destroyed, living in tents with only emergency food supplies to eat, many who survived the earthquake itself face a long hard winter and the risk of dying from hypothermia or malnutrition.

 

How did the government of Pakistan react? 

 

The army, with heavy lifting gear and helicopters, were sent into action immediately to search for survivors and provide treatment for the injured, emergency shelters and food.  Pakistan is not a wealthy country and high technology equipment was in short supply so in response to appeals other countries and international charities also provided help in the form of food, blankets, tents medicines and specialist rescue workers and medical personnel.

 

Useful links:

BBC Bitesize revision page about the Kashmir quake

BBC News report summary page with links to lots of articles

 

Lesson 8: The Los Angeles Quake, 1994 (an MEDC case study)

 

Learning objectives:

To know that LA is on a plate boundary and to be able to name the type of boundary and the plates involved.

To be able to recall at least 3 primary and 3 secondary effects of the LA quake.

 

The Northridge earthquake occurred on January 17, 1994 at 4:31 AM in a neighbourhood in the city Los Angeles, California. It lasted for about 45 seconds. The depth of the focus was about 10 miles. The earthquake had a strong magnitude of 6.8 on the Richter scale. 72 deaths were attributed to the earthquake, with over 9,000 injured. In addition, the earthquake caused an estimated $20 billion in damage, making it one of the costliest natural disasters in U.S. history.

 

Los Angeles lies on the boundary between the Pacific Plate and the North American Plate. Along the San Andreas fault, the two plates grind past each other. They are both going north-west, but at different speeds. The plate movements havev caused many other cracks or faults in the rock around the San Sndreas fault - one of which runs under Northridge. Two masses of rock were being crushed together along this fault. On 17th January 1994, the pressure just got too much and one mass of rock suddenly slipped upwards and set off the earthquake.

 

 

Here is a very early news report from NBC:

 

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These photos show just some of the destruction caused by the quake.

 

         

 

This map was made by the internet community to show how they were affected by the quake. Over 2000 people submitted data to help make this map.

 

 

The earthquake struck in the San Fernando Valley about 20 miles northwest of downtown Los Angeles near the community of Northridge. The actual epicentre of the quake was in Reseda. However, it took several days to pinpoint the epicentre with accuracy, and in the meantime the media had already called it "The Northridge Earthquake." The name stuck, in part due to the extensive damage and loss of life in Northridge.

 

Damage occurred up to 85 miles away, with the most damage in the west San Fernando Valley, and the cities of Santa Monica, Simi Valley and Santa Clarita. More than 30 people were killed in the tremor; a total of 61 deaths were attributed to direct and indirect causes. More than 8,700 were injured including 1,600 that required hospitalization. The Northridge Meadows apartment complex was one of the well-known affected areas in which sixteen people were killed as a result of the building's collapse. The Northridge Fashion Center and California State University, Northridge also sustained very heavy damage. The earthquake also gained worldwide attention because of damage to the vast freeway network, which serves millions of commuters everyday. The most notable of this damage was to the Santa Monica Freeway, Interstate 10, known as the busiest freeway in the United States, congesting nearby surface roads for three months while the freeway was repaired.

 

Additional damage occurred about 50 miles south in Anaheim as the scoreboard at Anaheim Stadium collapsed onto several hundred seats. The stadium was empty at the time. Although several commercial buildings also collapsed, loss of life was minimized because of the early morning hour of the quake, and because it occurred on a Federal holiday (Martin Luther King, Jr. Day). Also, because of known seismic activity in California, area building codes dictate that buildings incorporate structural design intended to withstand earthquakes. However, the damage caused by the earthquake revealed that some structural specifications did not perform as well as expected. Because of this building codes were revised.

 

Most casualties and damage occurred in multi-story wood frame buildings (e.g. the three-story Northridge Meadows apartment building). In particular, buildings with an unsteady first floor (such as those with parking areas on the bottom) performed poorly. Numerous fires were also caused by broken gas pipes due to houses shifting off foundations or unsecured water heaters falling over. In the San Fernando Valley, several underground gas and water mains were severed, and there were some streets where there were fires burning through floods. As is common in earthquakes, unreinforced masonry buildings and houses on steep slopes suffered damage. However, school buildings, which are required to be reinforced against earthquakes, in general survived fairly well.

 

Watch the video below for a quick recap of the key causes and consequences of the LA quake. Mind out - the tune is very catchy and may well get stuck in your head. You've been warned!

 

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The way in which the government responded to the LA quake was very different to what happened in Kashmir (our LEDC case study). Here are some of the key responses:

 

 

Useful links:

USGS slide show with located photos

USGS movie about the rupture

 

Lesson 9: Comparing the effects of earthquakes

 

Learning objectives:

To explain how the effects of earthquakes might vary among countries with different levels of economic development.

 

The effects of earthquakes vary between countries of different levels of economic development. Here are some of the reasons why...

 

LEDCs:

 

MEDCs: 

 

We looked at a superb BBC article which compared the China (Sichuan 2008), Italy (L-Aquila 1009) and Haiti (Port au Prince 2010) earthquakes and their effects. Some of the information is summarised below. You can read the full article by clicking the link here

 

The three quakes were of fairly similar magnitudes (between 6.3 and 7.9 on the Richter scale), but their effects were very different. The greatest number of people died in the Haiti quake, despite the fact that it was not the strongest of the three quakes. Very few people died, were injured or were made homeless in Italy. This is shown on the diagrams below.

 

 

          

 

The death rate (per number of people affected) was also much higher in Haiti (see diagram below):

 

 

The cost of the Haitian quake relative to the country's wealth was huge - much higher than in China or Italy. The high cost of the quake relative to GDP is likely to mean that the time taken to recover from the effects of the quake will be much longer than that experienced in Italy or China.

 

You can find out more about the Haitian quake by watching the videos below.

 

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Useful links:

S-Cool article on the impact of natural hazards in LEDCs and MEDCs

BBC Bitesize article on factors affecting the effects of an earthquake

 

Lesson 10:  Limiting the damaging effects of earthquakes

 

Learning objectives:

To consider how building design can reduce the damage experienced during an earthquake.

To link the possibility of building earthquake-proof buildings to a country’s wealth.

To be able to define and give examples of retrofitting, building code and appropriate technology.

 

People can't stop an earthquake from happening, and it is very difficult to predict exactly when an earthquake will occur. There are, however, a number of ways in which we can try to limit the damaging effects of earthquakes.

 

Most of the damage we associate with earthquakes involves human-built structures: people trapped by collapsed buildings or cut off from vital water or energy supplies. How a quake will affect the people of a city has a lot to do with how the city, its residents, and nearby governments have engineered structures and pipelines.

 

Building design is a very important way of reducing the damage caused by earthquakes. Many new buildings in MEDCs are earthquake-proof, and older buildings can be retrofitted to strengthen them (this means adding new technology to existing buildings). However, earthquake-proofing and retrofitting are very expensive and may not be appropriate in LEDCs. In LEDCs, appropriate technology will need to be used (see below).

 

When the ground beneath a building shakes, it makes the building sway as the energy of a quake’s waves moves through it. The taller a structure, the more flexible it is. The more flexible it is, the less energy is required to keep it from toppling or collapsing when the earth's shaking makes it sway. When planning the seismic safety of a building, structural engineers must design the support elements of shorter buildings to withstand greater forces than those of taller buildings.

 

Of course, the materials a building is constructed from also determine its strength, and again, flexibility is important. Wood and steel have more give than stucco, unreinforced concrete, or masonry, and they are favoured materials for building in fault zones. Skyscrapers everywhere must be reinforced to withstand strong forces from high winds, but in quake zones, there are additional considerations. Engineers must design in structures that can absorb the energy of the waves throughout the height of the building. Floors and walls can be constructed to transfer the shaking energy downward through the building and back to the ground. The joints between supportive parts of a building can be reinforced to tolerate being bent or misshapen by earthquake forces.

 

In addition to strengthening a building against earthquake shocks, engineers can actually reduce the force a building is subjected to. They install what are called base isolators, which isolate the base of the building from the earth's movements. Most are one of two forms. Some are like giant hockey pucks that squish and deform as the building rocks on top of them, absorbing some of the energy of the shaking. Others are sets of two horizontal surfaces, plates made frictionless so that they will slide past each other. The building sits on the top plates, the bottom plates rest on the ground. When the earth lurches, only the bottom plates move, sliding back and forth under the top plates.


As quake waves pass through the earth, they are filtered in different ways by different kinds of soils. Bedrock absorbs more wave energy than sandy soils or landfill, so buildings on solid rock will be much less affected than those built on softer soils. And if softer soils have water in them, they can become a little like quicksand during an earthquake. When seismic waves pass through saturated soil, they give it a strong squeeze. The soil loses its strength and behaves like a liquid, a process called liquefaction. Buildings on top of liquefied soil sink, and often topple.

 

This map of San Francisco's Marina district shows two sesimograms recorded during an aftershock of the 1989 Loma Preita earthquake in northern California. The seismograms were taken at the same time in locations less than 1100 feet from each other. One location is on solid bedrock, the other is on landfill. Can you work out which is which?

 

 

Answer: the greater shaking (on the left) is the area of landfill.

 

Building codes and regulations can also be important. Some western US states introduced rules as early as the 1930s. These have now been tightened even further and among the features now demanded are:

 

  • Specific configurations of steel-reinforced concrete
  • Foundations extending right down to bedrock
  • Stiffer building frames 
  • Facades that fasten on to the building's steel frame
  • Shatter-proof windows to prevent glass shards from causing lethal accidents 
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    This video from the National Geographic Channel describes how engineers have tried to build a quake-proof bridge in Japan.

     

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    Appropriate technology

     

    As mentioned above, many LEDCs are not able to aford to invest in retrofitting of old buildings or constructing earthquake-proofed new structures. Appropriate technology - technology which is designed with conideration of the community it is intended for - can be used instead. For example, over 1 billion people live in bamboo houses. This is because bamboo is very strong but it bends easily, so it can withstand the shaking of the earth in a quake. Bamboo is being used in Costa Rica (70 hectares of bamboo plantation will build 1000 houses) and when a strong earthquake hit in January 2009 almost all of the bamboo houses at the epicentre survived. All 30 bamboo houses that were in the epicentre of 7.6 magnitude Richter scale earthquake survived without any damage while many of the concrete homes and hotels around them collapsed

     

    Useful links: 

     

    BBC article: Can money stop an earthquake?

     

    Lesson 11: Preparing for earthquakes

     

    Learning objectives:

    To know what earthquake preparedness means.

    To know how people can plan and prepare for an earthquake. 

    To know what actions people can take following an earthquake.

     

    Earthquake preparedness means being prepared for an earthquake. If people are aware of what they should do before, during and after an earthquake, the number of casualties and the damage caused can be reduced. Children living in earthquake zones will be taught all about what to do during regular earthquake drills. In some areas, such as California. whole communities practice these drills, usually at least once per year.

     

     

    The Great California Shakeout is an annual programme which helps residents to prepare for 'The Big One'. More than 6.9 million people took part in 2009. Have a look at the video clip below to see how people are being encouraged to prepare for this quake.

     

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    FEMA suggests that the followings should be taken by all families to prepare for earthquakes:

     

     

    This advice (also from FEMA) is about what to do when the earthquake strikes:

     

    If you are Then:
    Indoors Take cover under a sturdy desk, table, or bench or against an inside wall, and hold on. If there isn’t a table or desk near you, cover your face and head with your arms and crouch in an inside corner of the building.
    Stay away from glass, windows, outside doors and walls, and anything that could fall, such as lighting fixtures or furniture.
    Stay in bed - if you are there when the earthquake strikes - hold on and protect your head with a pillow, unless you are under a heavy light fixture that could fall. In that case, move to the nearest safe place.
    Use a doorway for shelter only if it is in close proximity to you and if you know it is a strongly supported, loadbearing doorway.
    Stay inside until shaking stops and it is safe to go outside. Most injuries during earthquakes occur when people are hit by falling objects when entering into or exiting from buildings.
    Be aware that the electricity may go out or the sprinkler systems or fire alarms may turn on.
    DO NOT use the elevators.
    Outdoors Stay there.
    Move away from buildings, streetlights, and utility wires.
    In a moving vehicle Stop as quickly as safety permits and stay in the vehicle. Avoid stopping near or under buildings, trees, overpasses, and utility wires.
    Proceed cautiously once the earthquake has stopped, watching for road and bridge damage.
    Trapped under debris Do not light a match.· Do not move about or kick up dust.
    Cover your mouth with a handkerchief or clothing.
    Tap on a pipe or wall so rescuers can locate you. Use a whistle if one is available. Shout only as a last resort - shouting can cause you to inhale dangerous amounts of dust.

     

    People are usually taught to 'drop, cover and hold on'.

     

     

    Here is the video that will be played druing the drill:

     

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    And here is FEMA's advice about what to do after an earthquake:

     

     

    Useful links:

    USGS earthquake preparedness guide 

    Beat the Quake game from the Great Californian Shakeout