Waves & the Earth

Waves & the Earth

1. calculations

   • Speed

2. P1.20 Seismic Waves

   • P&S waves
     • Caused by earthquakes and Explosions
     • P waves - Longitudinal
       • Faster
       • Travel through liquids and solids
       • Primary Waves
       • Push - Longitudinal
     • S waves - Transverse
       • Slower
       • Travel through solids
       • Secondary Waves
       • Side to Side - Tranverse
     • Detected by seismometres
   • Reflection and Refraction
     • Seismic waves reflected and refracted
       • at boundaries between crust,mantle and core

3. 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 Waves = faster so arrive first
         • greater difference in time between waves=greater distance between seismometer and earthquake
         • 3. S Waves = slower so arrive second
           • 4. 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!

4. Tectonic plates

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