Question

at what time did the s wave arrive?
helena, montana
8:06 8:07 8:08 8:09 8:10 8:11
8:09
8:06
8:08
8:07
8:10
8:11

Explanation:

Step1: Analyze the seismograph

Look at the time - scale on the seismograph. The S - wave is represented by the second set of distinct waves.

Step2: Identify the arrival time

The first set of waves (P - waves) start around 8:07. The S - waves start at 8:09.

Answer:

8:09