Question

determining the earthquake distance
you can now determine the distance from each seismic recording station to the earthquake’s epicenter using the known times of travel of the s and p waves.
examine the graph to the right, a graph of seismic wave travel times. there are three curves on the graph: the upper curve shows s wave travel - time graphed versus distance, the center one shows p wave travel time versus distance, and the lower one shows the variation in distance with the difference of the s and p travel times. it takes an s wave approximately 70 seconds to travel 300 kilometers.
for practice, how long does it take the p wave to travel this same distance?
for the rest of this exercise you won’t be needing the individual s and p curves, only the s - p curve.
to determine the epicentral distance, we need greater resolution on graph. we will use the graph below, which shows an expanded part of the s - p curve.
graph: three curves (s - wave, p - wave, s - p) with time (seconds) on y - axis (10, 20, 30, 40, 50, 60, 70, 80) and distance (kilometers) on x - axis (100, 200, 300, 400, 500, 600, 700, 800)

Explanation:

Step1: Locate 300 km on x - axis

Find the point corresponding to 300 km on the horizontal (distance) axis.

Step2: Read P - wave time

From the 300 km point on the x - axis, move vertically until intersecting the P - wave curve. Then move horizontally to the y - axis (time axis) to read the value.

Answer:

It takes approximately 40 seconds for the P wave to travel 300 kilometers.