3 1. How do we measure seismic waves? Seismographs - Seismic waves travel through the Earth as vibrations. A seismometer is an instrument used to record these vibrations and the resulting graph that shows the vibrations is called a seismograph. The seismometer must be able to move with the vibrations, yet part of it must remain nearly stationary.
4 2. How do we read a seismograph? The record of an earthquake, a seismograph, as recorded by a seismometer, will be a plot of vibrations versus time. On the seismograph, time is marked at regular intervals, so that we can determine the time of arrival of the first P-wave and the time of arrival of the first S-wave.
6 Body Waves (Figure)- Waves moving through the body of the earth 3. Push-Pull, Primary (P) Waves - Compressional waves moving parallel to the direction of propagation. Can move through solids, liquids or gas.4. Shake, Secondary (S) Waves - Shear waves traveling or advancing at right angles to the direction of movement. Travel only through solids.
9 6. Surface waves travel over the Earth’s surface. Rayleigh waves, also called ground roll, travel like ocean waves over the surface of the Earth, moving the ground surface up and down. They cause most of the shaking at the ground surface during an earthquake.Love waves are fast and move the ground from side to side.
11 6. Surface WavesSurface waves are the slowest and by far the most destructive of the three types of seismic waves. Surface waves travel along the surface of the earth as two types of waves: Love waves are the fastest surface waves and move the ground from side-to-side, while Rayleigh waves (R-waves) roll along the ground just like a wave rolls across a lake or an ocean.Because it rolls, it moves the ground up and down, and side-to-side in the same direction that the wave is moving. Most of the shaking felt from an earthquake is due to the R-wave, which can be much larger than the other waves.