1. Aim: How do you locate earthquakes?
Locating Earthquakes
Aim: How do you locate earthquakes?

2. Introduction
After an earthquake has occurred, the time that the P- and S- waves arrived is picked up at a seismic recording station using a seismograph.
This information must then be decoded to determine where the earthquake actually occurred.
The further from the epicenter the greater difference in time between the arrival of the P- and S- wave.

3. I. Travel Time
The difference in time between the P- and S-waves arriving at a recording station.

4. II. Finding the distance to an earthquake’s epicenter
Step 1: Subtract the arrival time of the P-wave from the arrival time of the S-wave (express in minutes and in seconds) to get the travel time

5. Step 2 Using the E.S.R.T. (page 11) and a piece of scrap paper.
Line your scrap paper up along the travel time side.
Make two marks, one to represent 0 and the second to represent your travel time.

6. Example

7. Step 3
Using the two marks, slide your paper across the graph along the P- and S- curves, until the marks fit in between the two curves.
Your bottom mark will be touching the P-curve and your top mark will be touching the S-curve (as in the picture)

8. Step 4
Follow the marked edge of your paper down to the horizontal axis to find the distance to the epicenter.

9. Sample Problem
If the P-wave arrives at 8:02:00am, and the S-wave arrive at 8:05:00am. How far away from the epicenter is this city?
Answer: 1,800km