Figure 1. Partial seismograms for an earthquake. The P wave arrived at the BOH1 seismogram station at 10 minutes after 3:00pm (3:10pm). The second disturbance on the seismogram represents the arrival of the S wave. Using a ruler and the time-scale below: Measure the length of the initial P wave arrival to the initial S wave arrival.THA-2 PAK-4 CHI-3 6 Time Scale (secondr).