Seismograms and Earthquake Hunting

1. Seismograms and Earthquake Hunting

2. 1. Body Waves: P and S waves • P or primary waves • fastest waves • travel through solids, liquids, or gases • compressional wave, material movement is in the same direction as wave movement • S or secondary waves • slower than P waves • travel through solids only • shear waves - move material perpendicular to wave movement

3. 2. Seismometer • A seismometer is an instrument used to record vibrations in the Earth’s crust. • The graph that shows the vibrations is called a seismogram. • The seismometer must be able to move with the vibrations, yet part of it must remain nearly stationary. • *Most modern seismometers are computerized

4. 3. Seismograms • Provides information: • P wave arrival • S wave arrival • S-P interval • Amplitudes of each wave • What can be taken from this: • Distance of earthquake from seismograph • Magnitude of earthquake

5. 4. How is an Earthquake’s Epicenter Located? • Time-distance graph showing the average travel times for P- and S-waves. • 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

6. 5. Nomogram …Amplitude Decreases As Distance Increases… But Magnitude stays the same!! (M=5.5)

7. 6. How is an Earthquake’s Epicenter Located? • 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 • The intersection of the circles locates the epicenter