Seismographs are used to measure earthquake waves and locate earthquakes by analyzing the differences in arrival times of P and S waves recorded by multiple seismographs. Triangulating data from three or more seismograph stations allows the precise epicenter location to be found. Over 95% of major quakes occur in narrow zones that have been identified using this seismic location technique.

3. Focus, Epicenter, and Fault

5. Elastic Rebound Hypothesis

8. Seismograph

9. Earth’s Interior Showing
P and S Wave Paths

10. Seismogram

11. Measuring Earthquakes
Locating an Earthquake
 Earthquake Distance
• The epicenter is located using the difference
in the arrival times between P and S wave
recordings, which are related to distance.
 Earthquake Direction
• Travel-time graphs from three or more
seismographs can be used to find the exact
location of an earthquake epicenter.
 Earthquake Zones
• About 95 percent of the major
earthquakes occur in a few narrow zones.

12. Locating an Earthquake

14. Location You Found Actual Location