Seismology is the scientific study of earthquakes. The p-wave, or primary wave, is the fastest seismic wave and is measured with a seismograph to create a seismogram. The seismograph uses needles to record the waves on paper.
To find out the travel time of a p-wave or an s-wave, use the Earthquake Travel Time chart. When you find 6,500 km on the x-axis, you follow see that the p-wave line intersects at about 10 seconds. A related scientific field is called paleoseismology, which uses geology to study past earthquakes.
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To find the answer go to p. 11 of the Earth Science Reference Tables. Locate the P-wave line. Then locate 6500km on the x-axis of the P and S-wave chart. Follow the 6500 line up to the P line, when it intersects follow the line to the left and locate travel time.