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Seismic sensors collect earthquake data.Jason Reed/Photodisc/Getty Images
Examine the theoretical data in the following chart and note that the seismograph will record the times that the incoming P- and S-waves arrive at the location of the seismic recording stations.
Distance (km); P-wave travel time (min.); S-wave travel time (min.)
0; 0; 0
100; 2.33; 3.33
200; 4.0; 7.33
300; 5.67; 10.17
400; 7.00; 12.67
500; 8.33; 15.0 - 2
Seismograph data.Jason Reed/Photodisc/Getty Images
Convert the travel time from minutes to seconds for each set of waves. Since there are 60 seconds in a minute, multiply each travel time (minutes) to change the units. For example, multiply 2.33 minutes by 60 at the first location to get 139.8 seconds. Record these values on the data sheet in a separate column. - 3
Researchers use data from these graphs to determine travel times of the P- and S-waves.Comstock/Comstock/Getty Images
Construct a line graph. Label the x-axis as "Distance (km)" and the y-axis as "Time (seconds)." Plot the points for the S-waves on the graph in one color and the P-waves in another color. The data for each wave set should form a fairly straight line with time increasing with distance. - 4
S-waves cause more structural damage than P-waves.Stockbyte/Stockbyte/Getty Images
Use the following basic equation to calculate the velocity of the waves:
(seismic wave speed) = (distance from earthquake to seismometer)/(travel time). Two parameters must be known to calculate the velocity of waves: distance traveled and time. The distance represents the change of position of the wave as it moves along. Velocity of seismic waves is represented by units of distance divided by time and shown in units of km/min or km/sec.
(S-wave speed) = (distance from earthquake)/(travel time of S-wave)
(P-wave speed) = (distance from earthquake)/(travel time of P-wave) - 5
Locating earthquakes wave travel times.Central Press/Valueline/Getty Images
Estimate the distance to the epicenter with this equation:
(P-wave arrival time in seconds - S-wave arrival time in seconds) * 8 km/s = distance in km. The fact that P-waves and S-waves travel at different velocities can allow researchers to locate earthquakes. Seismographs can record both P- and S-waves but the intensity of the S-waves decreases with distance. Researchers can determine an approximate distance from the origin of a seismic wave to a location less than 200 km away by taking the difference in arrival time of the P-waves and the S-wave in seconds and multiply by 8 km/s, which is about the highest value for seismic wave velocity.
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