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Earthquakes

Earthquakes. Facts. About 500,000 occur yearly. Of those the vast majority aren’t even felt. On average, 1 magnitude 8 quake every year, somewhere. Large quakes can destroy cities, cause midslides, generate giant sea waves, burst damns or trigger volcanic eruptions. Facts.

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Earthquakes

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  1. Earthquakes

  2. Facts • About 500,000 occur yearly. Of those the vast majority aren’t even felt. • On average, 1 magnitude 8 quake every year, somewhere. • Large quakes can destroy cities, cause midslides, generate giant sea waves, burst damns or trigger volcanic eruptions.

  3. Facts • The deadliest quake ever occurred in China in 1557, killing an estimated 830,000 people (that’s like everyone in Nova Scotia).

  4. What is an earthquake? • Breaking or shifting of plates or rocks within the Earth. • Sends shockwaves rippling throughout the Earth.

  5. Where do they occur? • Along fractures in earth’s crust called faults. • The majority of faults are located along plate boundaries. • Sometimes they occur far from boundaries. These are called intraplate quakes. These are caused by a build up of stress within the plate due to the plate being stretched or squeezed.

  6. Causes • Plate tectonics (the movement of continental plates). • California • Iceland • Hawaii

  7. Waves • P waves • Spread in the crust from the focus alternately squeezing and stretching the rock as they travel through it. • S waves • Move slower than P waves and distort the rock in one direction and then another.

  8. Waves • Surface waves (cause most damage) • Love waves – moves surface of earth from side to side. • Rayleigh waves – move along the surface of the earth like a rolling ocean wave.

  9. Measurement and Recording • Focus (hypocenter) • Where the energy for the earthquake is stored (where the quake originates). • Epicentre • Point on Earth’s surface that is directly above the focus. • Usually the location of the greatest damage.

  10. Measurement • Seismograph • Makes tracings on paper which measure how much energy was released and how long the quake lasted. • Richter Scale • Assigns a number to the amount of energy released by an earthquake called magnitude. • A difference of magnitude 1 is equal to an earthquake being approximately 30 times more energy being released. • A difference if magnitude 2 is equal to 1000 times more energy being released.

  11. Richter Scale • Only noticeable with earthquakes of magnitude 4.0 or greater

  12. Measurement • Mercalli scale • Subjective/Personal scale that has people describe how the quake felt. • Scale • Number on the scale Damage and effects 1.Detected only by seismographs 2.Noticed only by sensitive people 3.Vibrations caused by heavy traffic 4.Usually felt by people standing. Rocking of free standing objects. 5.Sleepers awakened. 6.Trees sway, some damage from falling objects 7.General alarm, walls crack 8.Chimneys fall and there is some damage to buildings. 9.The ground starts to crack, houses start to fall, and pipes break. 10.Ground badly cracked and many buildings destroyed. Some possible landslides. 11.Few buildings remain standing, bridges destroyed, water, gas, electricity, and telephones become cut off. 12.Total destruction, objects are thrown into the air, much shaking, ground becomes cracked in many places. Tsunamis can also be created at this point.

  13. Prevention • Likely impossible • However, some ground is more solid than others • Bedrock is the best • Landfill is much worse • Fault zone is the worst • See example

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