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KS3 Geography - Tectonic Hazards: Earthquakes

A guide to tectonic hazards for your Year 9 course, compiled by your Librarians.

What is an earthquake?

   An earthquake is the shaking and vibration of the Earth's crust due to movement of the Earth's plates (plate tectonics). Earthquakes can happen along any type of plate boundary.

   Earthquakes occur when tension is released from inside the crust. Plates do not always move smoothly alongside each other and sometimes get stuck. When this happens pressure builds up. When this pressure is eventually released, an earthquake tends to occur.

   The effects of an earthquake can be devastating - they can destroy settlements, change landscapes, and cause many deaths.

What is the focus and epicentre of an earthquake?

   The point inside the crust where the pressure is released is called the focus (or hypocenter). The point on the Earth's surface above the focus is called the epicentre.

Focus and epicentre of an earthquake

   Earthquake energy is released in seismic waves. These waves spread out from the focus. The waves are felt most strongly at the epicentre, becoming less strong as they travel further away. The most severe damage caused by an earthquake will happen close to the epicentre.

What are the seismic waves of an earthquake?

   Earthquake energy is released in seismic waves. These waves spread out from the focus. The waves are felt most strongly at the epicentre, becoming less strong as they travel further away.

Properties of seismic waves

  p-waves s-waves
Type of wave longitudinal transverse
Relative speed faster slower
What can they travel through? solids and liquids solids only

P-waves are longitudinal waves like sound waves, and s-waves are transverse waves like light waves.


The most severe damage caused by an earthquake will happen close to the epicentre.

Can earthquakes be predicted?

   

 

   Scientists have tried many different ways of predicting earthquakes, but none have been successful. One basic idea behind quake prediction is that faults send out subtle but detectable warnings before they slip. Scientists have looked at a host of potential warning signals, or "precursors," including foreshocks, weird animal behavior, and changes in the water table, stream flow, well levels, and patterns of electrical currents in the ground. However, on any particular fault, scientists know there will be another earthquake sometime in the future, but they have no way of telling when it will happen.

Case studies of destructive earthquakes

You need to learn the causes and consequence of some major earthquakes from case studies. Click the images or links below to go to the case studies.

1989 San Francisco Earthquake

1989 San Francisco Earthquake

Test your knowledge about earthquakes!

1What is an earthquake?

2At what sort of plate boundaries might earthquakes take place?

3What causes earthquakes?

4The point inside the Earth where the pressure is released is called the:

5The point on the Earth's surface that is directly above an earthquake is called the:

6Energy released by an earthquake is in the form of:

7A seismometer measures what?

8The strength or magnitude of an earthquake is measured using what?

9What is an aftershock?

10What is a primary effect of an earthquake?

Animation of Earthquakes

A detailed earthquake presentation

Impact of earthquakes

   Earthquakes can destroy settlements and kill many people. Effects of earthquakes are often classified as primary and secondary impacts. Primary effects occur as a direct result of the ground shaking, eg buildings collapsing. Secondary effects occur as a result of the primary effects, eg tsunamis or fires due to ruptured gas mains. It is also possible to classify the impacts of an earthquake by taking the following factors into account:

  Social impacts Economic impacts Environmental impacts
Short-term (immediate) impacts People may be killed or injured. Homes may be destroyed. Transport and communication links may be disrupted. Water pipes may burst and water supplies may be contaminated. Shops and business may be destroyed. Looting may take place. The damage to transport and communication links can make trade difficult. The built landscape may be destroyed. Fires can spread due to gas pipe explosions. Fires can damage areas of woodland. Landslides may occur. Tsunamis may cause flooding in coastal areas.
Long-term impacts Disease may spread. People may have to be re-housed, sometimes in refugee camps. The cost of rebuilding a settlement is high. Investment in the area may be focused only on repairing the damage caused by the earthquake. Income could be lost. Important natural and human landmarks may be lost.

How to measure earthquakes?

   The size of an earthquake is measured on a Richter scale 0-10 of magnitude using an instrument called a "seismograph". Seismographs are basically pens suspended over a paper-covered rotating drum. When the earth trembles the pen makes a larger squiggle on the drum, allowing the size of the shaking to be measured. Each whole number on the Richter scale represents an earthquake 30 times larger than the number below it. Earthquakes that measure less than 3.0 are not usually felt, while one of 5.0 produces the same amount of energy as the Hiroshima atomic bomb. Earthquakes measuring around 7 or 8 on the Richter scale can be devastating. The largest recorded quake happened in Chile in 1960 and measured 9.5.

Earthquake safety


(Click a box above to learn more! Bigger version here)

BEFORE AN EARTHQUAKE:

  • Have a disaster plan.
  • Choose a safe place in every room. It’s best to get under a sturdy piece of furniture like a table or a desk where nothing can fall on you.
  • Practice DROP, COVER AND HOLD ON! Drop under something sturdy, hold on, and protect your eyes by pressing your face against your arm.
  • If you live in an earthquake prone area, bolt tall furniture to the wall and install strong latches to cupboards.
  • Prepare a disaster supplies kit for your home and car. Include a first aid kit, canned food and a can opener, bottled water, battery-operated radio, flashlight, protective clothing and written instructions on how to turn off electricity, gas, and water.

DURING AN EARTHQUAKE:

  • DROP, COVER AND HOLD ON!
  • Stay indoors until the shaking stops.
  • Stay away from windows.
  • If you’re in bed, hold on and stay there, protecting your head with a pillow.
  • If you’re outdoors, find a clear spot away from buildings, trees and power lines. Then, drop to the ground.
  • If you’re in a car, slow down and drive to a safe place. Stay in the car until the shaking stops.

AFTER THE SHAKING STOPS:

  • Check for injuries.
  • Inspect your home for damage.
  • Eliminate fire hazards, so turn off the gas if you think its leaking.
  • Expect aftershocks. Each time you feel one, DROP, COVER AND HOLD ON.

Earthquake simulation activity

Why do earthquakes occur? Learn about them in this activity!

Seismic waves activity

Understand how seismic waves work by playing the following activity!

Seismic waves simulation game

Play the following game to understand more about seismic waves!

How to locate an earthquake?

Earthquakes Q&A

Are you ready to answer the questions about earhquakes?


zondle - games to support learning

Experience the Haiti earthquake

   At 4:53 pm on January 12 2010, the worst earthquake to hit the Caribbean in 200 years struck the impoverished nation of Haiti. The epicentre of the 7.0-magnitude earthquake was only 25 kilometres from the country’s capital, Port-au-Prince. The damage was massive and immediate, with the death toll to reach 230,000

   What decisions would you make as an earthquake survivor, aid worker, or journalist in Haiti after the earthquake? Inside the Haiti Earthquake is a first-person simulation based on documentary footage from Haiti and real-life decision scenarios. Try it now below to obtain your first hand experience about the devastating earthquake.