- The point of how far an object can bend.
- Ex: Rubber band; Wooden Stick
- Rocks have an elastic limit .
- When pass their elastic limit, rocks break.
- When rocks break, they move along surfaces called faults .
- Rocks can move up, down, or sideways along a fault.
- Normal, Reverse, Strike-slip faults.
- Forces within Earth (CONVECTION) cause plates to move -> Puts stress on rocks.
Earthquake Distribution-I Fig. 4-7
How Earthquakes Occur
- Rocks move past each other along faults (B/c of tectonic plate movement).
- Rough surfaces of rock catch against each other.
- Plates continue to move despite stuck rocks.
- Rocks become stressed beyond their elastic limit , they break, move along the fault, and return to their original shape.
- To relieve stress, rocks will bend, compress, or stretch.
- If rocks break, the resulting vibration is an earthquake .
- Locations of earthquakes outline the tectonic plates .
- Seismic waves are the energy released when rocks break along faults.
- “ Focus” = the point at which this energy is first released.
- Seismic waves are produced and travel outward from the earthquake focus .
Types of Seismic Waves
- Cause particles in rocks to move back & forth in same direction .
- Secondary Waves (S-waves)
- Cause particles in rocks to move at right angles to the direction of the wave travel .
- Move rock particles in a backward, rolling, side-to-side, swaying motion .
- Most damaging type of seismic waves.
- Earthquake epicenter = the point on the Earth’s surface directly above the earthquake’s focus .
- Speeds of seismic waves allows us to determine how far away earthquake epicenter is .
- Measured with Seismograph .
Measuring Earthquakes-I http://quake.usgs.gov/recent/helicorders/Examples/M5.6_example.html http://earthquake.usgs.gov/image_glossary/seismograph.html
- Used to measure the strength of an earthquake .
- Based on the height of the lines on the seismograph.
- Scale has no upper limit, but 9.5 is estimated maximum.
- Used to measure the intensity of an earthquake based on the amount of damage caused by the earthquake.