1. Monitoring Earthquakes
Section 2-3

2. Seismograph Seismic waves cause drum to vibrate
Pen moves very little and records drums vibrations
Study arrival of P, S and surface waves on seismogram
Height of lines is greater for an earthquake close to the seismograph

3. Monitoring Faults Developed instruments to measure changes in:
elevation
tilting of land surface
ground movements along faults

4. Tiltmeter Measures tilting or raising of the ground
Like a carpenter’s level
Consists of two bulbs that are filled with liquid and connected by hollow stem
As the land rises or falls slightly, the liquid flows from one bulb to the other
Read scales to measure amount of tilting

5. Creep meter
Uses a wire stretched across a fault to measure horizontal movement of the ground
Wire is attached to a weight that can slide if fault moves

6. Laser ranging device
Uses laser beam to detect horizontal fault movements
Time laser beam as it travels from reflector back

7. GPS Satellites
Monitors changes in elevation and horizontal movement along faults
Measures tiny movements of markers set up on opposite sides of faults

8. Mapping Faults Detect seismic waves that reflect off of a fault
Helps map fault’s length and depth
Helps determine earthquake risk in an area

9. Earthquake risk in U.S.

11. Monitoring Changes along Faults
How rocks move along a fault depends on how much friction there is between the sides of the fault
When friction is low, rocks slide past without much sticking; earthquakes are unlikely
Where friction is moderate, sides of fault jam together; produce small earthquakes
Where friction is high, rocks lock together; stress builds up until an earthquake occurs

12. Trying to Predict Earthquakes
Even with data from many sources, geologists can’t predict when and where a quake will strike
Predicting earthquakes is one of the many scientific questions that remain unsolved!