1. Locating Earthquakes

2. Seismic wave behavior ► P waves arrive first, then S waves, then L and R ► Average speeds for all these waves is known

4. ► After an earthquake, the difference in arrival times at a seismograph station can be used to calculate the distance from the seismograph to the epicenter.

5. ► The farther away a seismograph is from the focus of an earthquake, the longer the interval between the arrivals of the P- and S- waves ► Use a Time-distance graph showing the average travel times for P- and S-waves. The graph shows the focus is about 9500 km from the seismograph

6. Three seismograph stations are needed to locate the epicenter of an earthquake ► A circle where the radius equals the distance to the epicenter is drawn on a map ► The intersection of the circles locates the epicenter

7. Richter scale ► measures total amount of energy released by an earthquake; independent of intensity ► Amplitude (height) of the largest wave produced by an event is corrected for distance and assigned a value

8. Height of largest wave is measured on seismograph Distance from epicentre to seismograph is calculated Data are plotted on the scale and a line is drawn from 1 scale to other Where the line crosses the magnitude scale is the Richter number

9. Richter Scale and Damage ► < 3.5 Generally not felt, but recorded. ► 3.5 - 5.4 Often felt, but rarely causes damage. ► Under 6.0 At most slight damage to well- designed buildings. Can cause major damage to poorly constructed buildings over small regions.

10. ► 6.1-6.9 Can be destructive in areas up to about 100 kilometers across where people live. ► 7.0-7.9 Major earthquake. Can cause serious damage over larger areas. ► 8 or greater Great earthquake. Can cause serious damage in areas several hundred kilometers across.

11. Richter Scale Math ► Increase by 1 whole number means a 10X increase in the Magnitude of the quake ► A magnitude 5.0 earthquake is 10 times the magnitude of a 4.0 quake

12. ► For every increase on the Richter Scale, the amount of energy released increases 30X Compare a 5.0 to a 7.0 quake ► 7.0 has 10 X 10 = 100 times greater magnitude ► 7.0 has 30 X 30 = 900 times more energy!

13. Earthquake Magnitude and Worldwide Occurrence ► MagnitudeAverage Number/Year ► Less than 2.0 600,000 ► 2.0-2.9 300,000 ► 3.0-3.9 49,000 ► 4.0-4.9 6,200 ► 5.0-5.9 800 ► 6.0-6.9 266 ► 7.0-7.9 18 ► Greater than 8.0 1