EarthquakesEarthquakes

Elastic LimitElastic Limit

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.

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.

FaultsFaults 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.

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-IEarthquake Distribution-I

Fig. 4-7

How Earthquakes OccurHow 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.

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.

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 WavesSeismic Waves

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.

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 WavesTypes of Seismic Waves1) Primary Waves (P-waves)

Cause particles in rocks to move back & forth in same direction.

Ex: Stretched Spring2) Secondary Waves (S-waves)

Cause particles in rocks to move at right angles to the direction of the wave travel.

3) Surface Waves Move rock particles in a backward, rolling, side-to-side, swaying motion. Most damaging type of seismic waves.

1) Primary Waves (P-waves) Cause particles in rocks to move back &

forth in same direction. Ex: Stretched Spring

2) Secondary Waves (S-waves) Cause particles in rocks to move at right angles to the direction of the wave travel.

3) Surface Waves Move rock particles in a backward, rolling, side-to-side, swaying motion. Most damaging type of seismic waves.

EpicenterEpicenter

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.

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-IMeasuring Earthquakes-I

http://quake.usgs.gov/recent/helicorders/Examples/M5.6_example.html

http://earthquake.usgs.gov/image_glossary/seismograph.html

Measuring EarthquakesMeasuring Earthquakes

Richter ScaleUsed 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.

Richter ScaleUsed 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.

Measuring EarthquakesMeasuring Earthquakes

Mercalli intensity scale Used to measure the intensity of

an earthquake based on the amount of damage caused by the earthquake.

Scale has 12 levels.

Mercalli intensity scale Used to measure the intensity of

an earthquake based on the amount of damage caused by the earthquake.

Scale has 12 levels.