Geo101_Lab6_Earthquakes

# Geo101_Lab6_Earthquakes - Geo101 Lab 6 Earthquakes Name_...

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Geo101 Lab 6 Earthquakes Name _________________________ Graphing seismic data and locating the epicenter of an Earthquake An earthquake produces three main types of seismic waves that radiate from its focus/ epicenter at different rates. Seismographs are instruments used to detect these seismic waves and produce a seismogram-a record of seismic wave motions obtained at a specific recording station (Figure 1). Figure 1. Seismogram of a New Guinea earthquake recorded at a location in Australia. Most of the seismogram shows only minor background deviations (short zigzags) from a horizontal line, such as the interval recorded between 7:12 and 7:14. Large vertical deviations indicate motions caused by the arrival of P-waves, S-waves, and L-waves of the earthquake (note arrows with labels). By making detailed measurements with a ruler, you can determine that the arrival time of the P-waves was 7: 14.2 (14.2 minutes past 7 o'clock), the arrival time of the S-waves was 7:17.4, and the arrival time of the L-waves was 7:18.3. Seismograms can detect and record several types of body waves, which are seismic waves that travel through Earth's interior (rather than along its surface) and radiate in all directions from the focus. Two of these body waves are used to locate earthquake epicenters:

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Figure 2. Partical motion of S and P waves. • P-waves : P for primary, because they travel fastest and arrive at seismographs first. (They are compressional, or "push-pull" waves.) • S-waves : S for secondary, because they travel more slowly and arrive at seismographs after the P-waves. (They are perpendicular, shear, or "side-to-side" waves.) Seismographs also detect the surface seismic waves, called L-waves or Love waves (named for A. E. H. Love, who discovered them). L-waves travel along Earth's surface (a longer route than the body waves) and thus are recorded after the S-waves and P-waves arrive at the seismograph. Figure 1 is a seismogram recorded at a station located in Australia. Seismic waves arrived there from an earthquake epicenter located 1800 kilometers (1125 miles) away in New Guinea. Notice that the seismic waves were recorded as deviations (vertical zigzags) from the nearly horizontal line of normal background vibrations. Thus, the first pulse of seismic waves was P-waves, which had an arrival time of 7:14.2 (i.e., 14.2 minutes after 7:00). The second pulse of seismic waves was the slower S-waves, which had an arrival time of 7:17.4. The final pulse of seismic waves was the L-waves that traveled along
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## This note was uploaded on 12/28/2009 for the course 460 101 taught by Professor Swisher during the Fall '09 term at Rutgers.

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Geo101_Lab6_Earthquakes - Geo101 Lab 6 Earthquakes Name_...

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