A. Identify the P-wave arrival on each seismogram. I would mark it with a vertical arrow or line and the letter P. The P-wave arrival is the start of the first large peak or trough, the beginning of the wave that deviates from the normal background wiggle. Hint: the P-wave arrival for the CAN record is at 2.5 minutes from the beginning of its record. B. Identify the S-wave arrival on each seismogram, and mark it with a vertical arrow or line and letter S. The S-wave always arrives after the P-wave has come and decayed, and it is always higher amplitude than the P. Pick the S- wave arrival as the start of the first large peak or trough of the packet of many high-amplitude S-waves. Hint: the S-wave arrival for the CAN record is at the beginning of the sharp downward trough at 9.3 minutes. CAN meccet 1 min QUE m PEK PS Time osales) Figure 1. Seismograms from three stations for the same earthquake. Scale bar and tic marks in seismograms indicate 1 minute. 11 10 9 8 JAKMANY www 7 Dim Figure 2. Graph showing the relationship between P-to-S lag time and distance. Knowing the P-to-S lag time, one can determine distance to the epicenter. 4 500 4.00 300 100 Datance -30 t 00 40- 5 24 20- 7.71 sed 1 Mag 35.3% - Amplitude 23 mm 100 50 10 2 1 200 02 Of Figure 4. Example seismogram (top) with nomogram (bottom) for determining earthquake Richter magnitude, from Richter's 1958 book, Elementary Setmology, The nomegram allows a simple conversion from S-to-Plag time to distance to the epicenter (left asis). A line connecting distance and the seismogram's wave amplitude (right axis) intersects the middle axis at the earthquake's magnitude. Note that the left and right axes