GL102 Lecture Notes - Lecture 5: Seismic Moment, Seismogram, Shallow Focus
Document Summary
Seismometers are usually placed in clusters of three to record the motion along the x, y, and z axes of three-dimensional space. A seismometer by itself cannot record the motion that it measures. A seismograph is a recording device that produces a permanent record of earth motion detected by a seismometer, historically recorded as wiggly lines drawn on a moving strip of paper, but now digitally recorded. The record of earth vibration is called a seismogram. The seismogram can be used to measure the strength of the earthquake. Within minutes after an earthquake occurs, distant seismographs begin to pick up seismic waves. A large earthquake can be detected by seismographs all over the world. Because the different types of seismic waves travel at different speeds, they arrive at seismograph stations in a definite order: first the p waves, then the s waves, and finally the surface waves. These three different waves can be distinguished on the seismograms.
