Waves & the Earth

Waves & the Earth

1. P1.18 Infrasound

   • frequencies
     • humans hear between 20Hz-20,000Hz
     • infrasound - below 20Hz
   • uses
     • communication between animals
       • e.g. whales&elephants
     • detecting animal movement in remote location
     • detecting volcanoes&meteors
   • calculations

2. P1.19 Ultrasound

   • frequencies
     • ultrasound - above 20,000Hz
   • uses
     • sonar
       • find depth of water below boat
     • communication between animals
       • e.g. bats&dolphins
     • foetal scanning
   • calculations

3. P1.20 Seismic Waves

   • P&S waves
     • caused by earthquakes+explosions
     • P waves=longitudinal
       • faster
       • travel through liquids+solids
     • S waves=transverse
       • slower
       • travel through solids
     • detected by seismometres
   • reflection&refraction
     • seismic waves reflected&refracted
       • at boundaries between crust,mantle+core

4. P1.22 Detecting Earthquakes

   • hard to predict when
     • unsure of size of forces acting on tectonic plates
     • unsure of amount of friction on plates
   • locating earthquakes
     • 1. many seismometers detect P&S waves
     • 2. P=faster so arrives first
       • greater difference in time between waves=greater difference between seismometer+earthquake
     • 3. scientists work out distance from each seismometer
       • find out where earthquake happened
     • at least 3 seismometers used
   • causes of earthquakes
     • 1. tectonic plates move due to convection currents in mantle
     • 2. plates slide past each other
     • 3. friction-don't slide smoothly
     • 4. forces build up till part of plate breaks
     • 5. plates move with sudden jerk-earthquake!

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