Earthquakes

What you will learn• Explain the terms focus, tremor, epicentre• Know how earthquakes are measured• Briefly describe the different types of

earthquake waves• Describe the effects of earthquakes using case

studies• Describe how to predict and prevent

earthquake damage. • Know how this topic appears on the exam

paper.

Earthquake Keywords

• Focus• Epicentre• Tremors• Aftershocks• Fault

Activity

• Work in pairs to remember what these keywords mean.

Class Activity

• Using your textbook and working in pairs define the keywords into your copy.

Did you know…..?

• California has suffered from extreme earthquakes in the past….

• This is because California is located where the Pacific and the American plate slides past each other

• The boundary between the two plates is called the San Andreas Fault

Clip of San Andreas Fault

• http://www.youtube.com/watch?v=hReS4Fm94L4

How do earthquakes occur?

• From junior cert you should know that earthquakes occur when two plates slide past each other. (Conservative plate boundary)

• In Leaving Cert geography you learn that earthquakes can occur for many reasons

• Activity: Work in pairs and using information from page 30 of your book summarise the main ways in which earthquakes occur.

Where do Earthquakes occur?

The most active place for earthquakes is the Pacific Ring of Fire.

Earthquakes occur at all types of plate boundaries.

1.Shallow Earthquakes : continental- continental plate collision and conservative boundaries. Associated with mid ocean ridges. (70km below the surface)2.Intermediate earthquakes : oceanic -continental plate collision (70 -300km)3.Deep earthquakes : oceanic -oceanic plate collision (greater than 300km)

Earthquake Waves (tremors)There are 3 types of waves

1.P Wave or compressional waves – shake the ground back and forth in the same direction as the wave. Very fast so little damage

2.S Wave or Shear wave – shakes the ground back and forth perpendicular to the direction of the wave. Travel more slowly after the P wave can cause damage

3.Surface Waves – travel slowly and move the surface of the earth up and down and sideways. Can cause serious damage. Can be called Love and Rayleigh waves.

P Waves

S waves

Surface waves

Recording and Measuring Earthquakes Key Words

• Seismographs• Richter Scale• Modified Mercalli Scale

Activity

• Read the handouts given on recording and measuring earthquakes

• Summarise in your own words the differences between the Richter and modified Mercalli scale.

The Effects of Earthquakes

Can you think of some of the immediate and long term effects of an earthquake

Immediate Effects

1. Death and destruction2. Tsunamis3. Gas explosions, fires, loss of fresh water4. Homelessness5. Liquefaction: Deep loose soils or reclaimed

land. The ground turns to liquid due to intense shaking of the ground. This causes buildings to sink into the ground e.g. Mexico City, LA

Long Term Effects

1. Migration2. Disease – water and sewerage pipes burst

and take time to repair3. Economic slowdown: shops close, industry is

destroyed and government spending is diverted from other projects.

Tsunami

• Another effect is a tsunami e.g. The South East Asian Earthquake and Tsunami 2004

• An earthquake occurs under the sea, the movement of the sea floor causes ripples on the sea surface. The ripples travel very fast.

• One of the first warning signs of a tsunami can be a rapid withdrawal of water from the beach.

Activity

• Read the case study of the 2004 earthquake and tsunami.

• Summarise what happened and the effects in your own words into your copy books.

Tsunami Warning Systems

• Tsunami watch• A weather radio system • US Coast Guard broadcasts urgent messages• Local Authorities implement an evacuation

plan.

Haiti Earthquake January 2010

• Population of 10million, live on €1.50 a day.

• Located on the conservative plate boundary between the Caribbean plate and the North American plate.

• 12th January 7.0 earthquake on the Richter scale killed 230,000 people.

Cause

• The quake occurred where the Caribbean plate moves east away from the North American Plate by 20mm per year.

• Shallow quake. The focus was just 13km deep. The epicentre was about 25km from the capital city Port-au-Prince.

Immediate Effects1. 222,570 killed. 300,000 injured. 2. Over 1.3million people were left homeless3. Widespread devastation and damage. 90% of the buildings in

the capital city were destroyed or heavily damaged including a prison with 4,000 inmates who escaped.

4. Damaged the harbour which made it unusable for immediate rescue and aid operations.

5. Telecommunications (phone and tv) were damaged. 6. Lack of hospitals, morgues and medical supplies held up

rescue attempts. 7. Aftershocks stopped people from being rescued.8. Emergency medical aid from around the world was sent.

Long Term Effects1. Brazil offered €140 million donation for long

term aid. The world’s bank cleared the country’s debt repayments for five years.

2. Haiti’s government estimated the damage at €7 billion.

3. A severe outbreak of cholera in the months following the earthquake led to deaths.

Predicting Earthquakes• Studying seismograph activity to see which

areas might be next.• Measuring crustal stress levels• Measuring ground tilting with lasers.• Measuring radon gas emissions from wells and

rocks which often increase when rocks are under pressure.

• Observing unusual animal behaviour (not the most helpful)

Earthquake Proof Buildings

1. Secure all items to the wall. 2. A bar across the front of cupboards to stop jars and

tins from falling out. 3. Secure or fix all furniture to the walls or floors4. Shatterproof windows5. Building foundations should have ‘seismic isolators’

which absorbs the force of the quake and reduce the movement of the building.

6. Extra supports are attached to the corners on each floor to support the building as it shakes.

Activities1. Explain the terms focus, epicentre,

aftershock, tremor, earthquake. 2. What is a tsunami? Why are they so

devestating?3. Describe four of the methods used in

earthquake prediction. 4. Describe the causes and effects of the Asian

tsunami5. Examine the methods used to reduce the

destructive effects of earthquakes.