Recording Board Difference in arrival times: San Francisco: 4:10 2,800km 1,000 2,000 3,000 4,0005,000 Open your compass to the EXACT distance on the scale.
Finding the Earthquake Origin Time You take a distance to epicenter that you have already determined, or one given to you Let’s say the epicenter distance is 4400km, and the arrival time is 3:21:15 PM Well, use your ESRT and do some time math!!! Let’s try it
Do it! Find the distance on the horizontal axis. Go up to the point where you hit the P- wave travel line. Go over to the vertical axis and read off the travel time for the P- wave. P wave travel time = 00:07:40 Epicenter dis = 4400km
Now, do the math! Take the arrival time, and subtract the travel time from it! 3:21:15 – 00:07:40 = 3:13:35 So, the origin time of the Earthquake is 3:13:35 PM. Now YOU try it for San Francisco!!