GLG 112 1st Edition Lecture 12Outline of Last Lecture I. Introduction to earthquakesA. Earthquake locationsB. What is an earthquake?C. Elastic rebound theoryII. Earthquake termsOutline of Current Lecture I. Seismic WavesA. Body Waves1. P-waves (primary)a. Speedb. Movement c. What we feel2. S-waves (secondary)a. Speed b. Movementc. What we feelB. Surface wavesII. Measuring seismic wavesCurrent LecturePrimary waves are the fastest seismic waves at a speed of 4 miles per second. They have a push pull motion. In other words, they vibrate in the direction they are traveling. They can also be called compressional waves. These waves travel through solids and liquids and radiate from the focus of the earthquake. When they occur we feel a vertical jolt at the service. Secondary waves occur after primary waves and travel a bit slower at 2 miles per second. Thesecan also be called shear waves because the move sided to side like a snake. In other words, theyvibrate perpendicular to their travel direction. If we felt these at the surface we would feel side to side motion. Surface waves are the last to arrive, have lots of different motion, and are the most destructive. These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.There are three things you need to know about measuring seismic waves. First, you should know the difference between a seismograph and a seismometer. A seismograph is an old version of a seismometer. It measures the ground shaking with the use of a pen, paper, and weight (that holds the pen in place). A seismologist would need to have two of these, one to measure vertical motion and one to measure horizontal motion. A seismometer is a newer, computerized version of this. Only one machine is required. With this new technology, the computer just tells the pen what to mark in an earthquake. These instruments are very sensitiveand will pick up almost any kind of ground movement almost anywhere. The one on this campus is probably picking up all sorts of data from the construction all around it. Finally, a seismogram is the written record made by these
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