1. Locating Earthquake Epicenters
1) Find p-wave and s-wave arrival times

2. 2) Subtract p and s wave arrivals (Go to p. 11 ESRT)
3) Use scrap to mark the difference (00:01:30) on the Y axis. Slide until the bottom mark touches the P line and top mark touches the S line.
5) Go to the map!!!
4) Drop Down to read the Epicenter distance.
Subtract  Mark  Slide Drop Down

3. a) Mark Radius for each city (1000 km)
b) Make circle with compass
c) Intersection triangle is where the earthquake happened

4. Origin Time
Practice #1: Kyle arrived at school at 8:03:00 am. It took him 00:08:20 (8 minutes 20 seconds) to walk to school. What time did Kyle leave his house?
Practice #2: An earthquake p-wave arrived at 11:23:00 pm. The p-wave travel time was 00:03:20. What time did the earthquake originate?
**In order to calculate origin time you must subtract the p-wave travel time from the p-wave arrival time.**

5. 6) Find Origin Time (should be the same for all 3 locations)
P wave arrival(00:01:00)
– P travel (?)
Origin time
How do I find the P travel time?
Use epicenter distance (1000 km)
scroll up to P line…
head over to Y axis and read the P travel time. (00:02:20)

6. Recap 1) Find P and S wave arrival times
2) Subtract arrival times (go to page 11 ESRT)
3) Mark the difference. Slide until it’s snuggled between both P and S lines
4) Drop down to read epicenter distance.
5) Go to the map: radii (3), draw circles (3), x marks the spot!
6) Origin Time: P arrival – P travel*.
Use epicenter distance, scroll up to P line…head over to Y axis, and read P travel time.