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Transcript
Before you look in more detail about earthquakes you first need to understand the structure of the earth Key PointOuter core is liquid! The Earth is almost a sphere. These are its main layers, starting with the outermost: • • • • crust - relatively thin and rocky mantle - has the properties of a solid, but can flow very slowly outer core - made from liquid nickel and iron inner core - made from solid nickel and iron Tectonic Plates? • The outermost layer of the Earth is made up of tectonic plates. • These plates are slowly moved by convection currents. Convection currents cause the plates to move.... Convection currents can lead to earthquakes... • Radioactive decay takes place in the mantle, this produces a lot of heat, which causes the mantle to flow in convection currents. The hot rock rises then cools, causing the plates to move. As the plates move they slide past each other. There is friction between the plates. Sometimes they get stuck, the pressure and energy builds up. Eventually they slip releasing the energy as an earthquake. Seismic Waves? • These are waves that travel through the earth when an earthquake occurs. You need to learn the properties of the two types of waves. Key Point- Seismic waves like any other waves will refract! Key Points • S waves cannot pass through the liquid outer core, but P waves can. When P waves pass from solid to liquid, then from liquid to solid, there are sudden changes in direction – they are reflected and refracted. Seismic waves are also reflected and refracted as they pass into different rock types. Seismometers are machines that can detect seismic waves Detecting earthquakes • Earthquakes are detected using a seismometer – a piece of equipment that picks up the vibrations in the earth. A scientist can work out the location of an earthquake by calculating the time difference between the arrival of the S and P waves. Information from three different seismometers is compared to work out the exact location of the earthquake – the epicentre. This is called triangulation.