1. Measuring Earthquakes
How are earthquakes measured?

2. Seismology The study of earthquake waves is called Seismology
Earthquake waves can be detected at great distances by Seismometers
A seismometer’s record is known as a seismogram

4. Time-Travel Curves
Years of data collection has led to time-travel curves
The curves tell the time an S- and P-wave takes to reach a certain distance
P-waves arrive first
The difference between waves on a seismogram determines the distance from the epicenter

5. Time-Travel Curves

6. Locating Earthquakes
Epicenters are located by the separation between S- and P- waves on a seismogram
Cannot use one location to map epicenter
Need to use three or more seismic stations
Time can be measured in same way

7. Earthquake Intensity
The amount of energy released during an earthquake is known as its magnitude
Three scales measuring intensity
Richter Scale
Moment Magnitude Scale
Modified Mercalli Scale

8. Richter Scale
The Richter Scale is based on the largest waves generated by the quake
Each number on the scale is an increase of 10
Ex: 8 is 10x larger than 7, 100x larger than 6

9. Moment Magnitude Scale
The Moment Magnitude Scale includes:
Size of fault rupture
Amount of movement along fault
Rocks’ stiffness
Uses more data than Richter Scale – More accurate

10. Modified Mercalli Scale
The Modified Mercalli Scale assesses damage from a quake

11. Factors affecting Magnitude
Distance from epicenter
Depth of focus

12. Where do Earthquakes Occur?
Earthquakes are not randomly distributed
Almost 80% of Earthquakes occur along the Circum-Pacific Belt