Earthquakes

• HOW?

• WHERE?

• SEISMIC WAVES

How do earthquakes occur?•Definitions:

• Earthquake – A sudden and violent shaking of the earth. Is caused by movement of the plates in the Earth’s crust.

• Focus – This is the place where the earthquake starts and can be several kilometres beneath the Earth’s surface.

• Epicentre – The area on the Earth’s surface directly above the focus, this is where Seismic Waves first reach the surface.

•Richter scale – The instrument used to measure the seismic waves of an earthquake.

Terms

Earthquakes

Strength of Earthquakes

The Richter Scale

• It measures the size of the seismic waves and their speed to classify the magnitude of the earthquake in terms of energy released.

• The scale extends from 1 – 9 .

• Each step represents a magnitude 10 times greater than the previous step.

• Exponential scale

What produces an earthquake ?

• Plate movements cause cracks or faults in the earth’s crust.

• These faults produce stresses which cause vibrations.

• These vibrations are called earthquakes.

P, S and L Waves

• The P and S waves pass through the crust from the focus to the surface.

• On the surface they become L waves where they cause the most damage .

• They cause movement in the following three ways:• P - backward and forward

• S - from side to side

• L - up and down

Activity 12: Earthquake concepts, p123• Definitions:

• 1. Tectonic plates: Large segments of crust into which the Earth’s surface is broken

• 2. Focus: The place underneath the surface where the earthquakes originates

• 3. Epicentre: The areas ON the Earth’s surface immediately above the focus

• 4. Seismograph: Instrument used to measure shock waves

• 5. Richter Scale: Scale (1-10) used to compare the intensity of earthquakes

Tsunamis

• They are huge sea waves which are experienced in shallow waters along coastlines.

• It reaches heights of between 10 and 30 meters.

• Develops when earthquake in sea is larger than 7.5

Large Earthquakes that occur under the ocean can cause tsunamis

Tsunamis

ACTIVITY 13: The Impact of Earthquakes and Tsunamis, p125DESTRUCTION CAUSED BY EARTHQUAKES DESTRUCTION CASUED BY TSUNAMIS

People are injured or killed People are injured or killed

Buildings collapse – many people homeless Buildings collapse – many people homeless

Infrastructure damaged (roads, bridges, railways)

Infrastructure damaged (roads, bridges, railways)

Electricity, gas and water supplies are disrupted due to broken cables and pipes

Electricity, gas and water supplies are disrupted due to broken cables and pipes

Dam walls may break and cause landslides and mudslides

Children may be separated from parents

Shortage of fresh drinking water Loss of livestock and pets

Shortage of food and medical supplies Possessions are destroyed and damaged

Disruption of sewage system and danger of cholera

Erosion occursCrops may be washed away

Settlements cut off from rest of world

Strategies to reduce the impact of earthquakes

• Government strategies:

- Install adequate warning systems.

- Have a unified plan of action

- Provide information to create awareness

- Have the necessary equipment for rescue operations.

- Provide rapid and efficient services after an earthquake.

Strategies to reduce the impact of earthquakes

• Safer buildings:

-Laws to abide by certain building regulations.

-Special designed frames, triangular shapes, rollers, shock absorbing materials etc.

- Poor counties often don’t enforce building regulations- hence the larger death toll during earthquakes.

Strategies to reduce the impact of earthquakes

• Community strategies:

- Check hazards at home.

- Identify safe places to go to when an earthquake starts.

- Educate

- Have disaster supplies ready

- Help the community to prepare.

Case Study 1: The Indian Ocean Tsunami, 26 December 2004 (p127)

• 1. 9,4 on Richter Scale

• 2. Near total destruction, visible waves in the crust

• 3. An undersea earthquake causes a massive rise and fall in the ocean floor. Crustal waves cause the sea level to rise. When the tsunami nears land it slows down. The sea pulls back and a big wave is created as the tsunami reaches land.

• 4. Landslides and volcanic eruptions

• 5a) Indian and Burmese plates

• 5b) Destructive margin

• 5c) No. Severe earthquakes are found at these plates

• 6) About 250 000 people died

• 7) Early warning systems, geological surveys. Educate people about the signs of incoming tsunamis, planned evacuation routes

Case Study 2: The Japan Earthquake and tsunami (p128)

• 1) Bridges destroyed, very few structures were left standing.

• 2) They could not escape

• 3) Nuclear plants, bullet trains

• 4) Could cause radiation

• 5) Buildings built from weaker materials, no early warning, people were not educated enough, few geologists, densely populated

Unit 4: Questions on Earthquakes (p130)

• 1a) A

• 1b) A

• 1c) D

• 1d) C

• 1e) D

• 2) See answers to Activity 13, write an article mentioning at least 6 effects

• 3) Precautions: Find active fault zones by means of geological survey, Identify high risk areas, Predict When and Where earthquakes are most likely to occur, Emergency services should be ready to be mobilised quickly, Build dams along fault lines to absorb shocks, Strengthen existing roads, houses and bridges, build earthquake resistant buildings,

• 4a) Focus

• 4b) Destructive margin

• 4c) Oceanic crust is forced downward, pressure increases

• 4d) Tsunami; focus under the sea; fires; bridges destroyed; airport destroyed;

• Bullet train route destroyed; deaths in train; people died in cities Osaka and Kobe; destruction in cities Osaka an Kobe

Unit 4: Questions on Earthquakes continued