2-Seismic-Waves.pptx

The Earth’s Interior Layers of the Earth Crust Mantle Core Outer Core Inner Core Seismic Waves A wave of energy that is generated by an earthquake or other earth vibrations and that travels within the Earth or along its surface Seismologists use seismographs to record the am...

The Earth’s Interior Layers of the Earth Crust Mantle Core Outer Core Inner Core Seismic Waves A wave of energy that is generated by an earthquake or other earth vibrations and that travels within the Earth or along its surface Seismologists use seismographs to record the amount of time it takes seismic waves to travel through different layers of the Earth. Earth’s different densities and stiffness, makes the waves refracted or reflected. Parts of a Wave  Crest- highest point of a wave  Trough- lowest point of a wave  Amplitude- distance from the undisturbed surface to crest or trough  Wavelength- distance in which the wave repeats often measured from crest to crest  Wave height- the vertical distance from crest to trough  Period- the time for a wave to pass a fixed point  Frequency- number of waves per unit time Two Main Types of Seismic Waves and its Sub-types Body Waves Primary Waves Secondary Waves Surface Waves Love Waves Rayleigh Waves Body Waves Can travel through the Earth’s inner layers Used by scientists to study the Earth’s interior Have higher frequency than surface waves Primary Waves also known as P-wave or Compressional Wave travel at the greatest velocity through the Earth they are the first waves to be recorded by a seismograph during an earthquake they propagate through a material by alternately compressing and expanding the medium can travel through solids, liquids and gases Secondary Waves also known as secondary waves, shear waves or shaking waves travel slower than P-waves particle motion is perpendicular to the direction of wave propagation Moves rocks up and down or side-to-side Cannot travel through liquid Epicenter Surface Waves  can travel through the surface of the Earth  Arrives after the body waves and are confined to the outer layers of the Earth  generated when the source of the earthquake is close to the Earth’s surface  they can be much larger in amplitude and can be the most destructive type of seismic wave Love Waves Named after Augustus Edward Hugh Love, a British mathematician who worked out the mathematical model for this type of wave in 1911 travel slightly faster than Rayleigh waves Moves the ground in a side-to-side horizontal motion, causing the ground to twist Causes the most damage  Rayleigh Wave  Named after John William Strutt, Lord Rayleigh who mathematically predicted the existence of this type of wave in 1885  also called ground roll, travel as ripples similar to those on the surface of water  Rayleigh waves can be observed during an earthquake in open spaces, such as parking lots where the cars move up and down with the waves Importance of Studying Seismic Waves The different behavior of waves in different materials helps seismologists deduce the composition of Earth layers It helps us to locate and understand fault lines and the stresses and strains acting on them. Also used in the search for oil and gas by explosions or ground vibrators. Rayleigh Surface Waves Body Waves Rayleigh Guide Questions  Q1. Differentiate surface waves from body waves.  Surface waves travel only on the Earth’s surface like ripples of water while body waves travel through the Earth’s body (interior). In addition, surface waves arrive last at seismic recording stations compared to the body waves.  Q2. Which type of wave do you think were useful to seismologists in their study of the Earth’s interior? Explain your answer.  The body waves were used by seismologists because they can pass through the Earth’s interior.