+ Earthquakes

+What You Will Learn

You will learn about earthquakes and how they are measured.

You will learn :

what tools are used to measure earthquakes

what scientists learn from measuring earthquakes

+VOCABULARY:

Earthquake

Seismology — the study of earthquakes

Seismologist — a scientist who studies earthquakes

Epicenter

Seismic Wave

Seismometer — a tool scientists use to measure the strength of seismic waves

Magnitude

Richter Scale

+Review: Lithosphere

Tectonic plates are large slabs of crust that move on Earth's mantle.

Faults are fractures in Earth's crust.

Three Types of Faults

Strike-SlipThrust

Normal

+What are Earthquakes?

Vibrations in Earth's lithosphere caused by a sudden release of energy. 

The energy is released in the form of seismic waves, or waves that travel through Earth. 

+2 Locations:

The location below Earth's surface where an earthquake starts is called the hypocenter. 

The location on Earth's surface directly above the hypocenter is called the epicenter. 

+Seismic Waves

P waves, ( "primary" or "compression" ) waves.

shake the ground back and forth, parallel to the direction the waves are traveling.

P waves travel faster than S waves

S waves, ("secondary" or "shear”) waves.

 shake the ground up and down, perpendicular to the direction the waves are traveling.

S waves are more destructive

+ Primary Waves (P Waves)

• A type of seismic wave that compresses and expands the ground

• The first wave to arrive at an earthquake

+ Secondary Waves (S Waves)

A type of seismic wave that moves the ground up and down or side to side

+Comparing Seismic Waves

+Surface Waves

Move along the Earth’s surface

Produces motion in the upper crust Motion can be up and down Motion can be around Motion can be back and forth

Travel more slowly than S and P waves

More destructive

+

Measuring Earthquakes:

Seismographs, ("seismometers,”) - instruments used to record earthquakes.  Seismograms - the recordings made by the instruments.

+ Typical Seismogram

http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt

+Measuring Earthquakes: Seismograms

Scientists use seismograms to determine the sizes of earthquakes. 

Magnitude: the size of an earthquake

-a measurement of the amount of energy released during an earthquake. 

Richter Scale: a mathematical formula that assigns numbers to earthquakes. (size of the earthquake)

+How do scientists calculate how far a location is from the epicenter of an earthquake?

• Scientists calculate the difference between arrival times of the P waves and S waves

• The further away an earthquake is, the greater the time between the arrival of the P waves and the S waves

+Richter Scale:

logarithmic, meaning that a difference of one unit represents a tenfold difference in size.  For example, an earthquake measuring 5.0 on the Richter scale is 10 times larger than an earthquake measuring 4.0, 100 times larger than an earthquake measuring 3.0, 1000 times larger than an earthquake measuring 2.0, and so on.

+

Locating Earthquakes:

Triangulation-a triangle has three sides, and it takes three different seismographs to find the location of an earthquake's epicenter.

The location where the three circles intersect, or cross each other, is the epicenter. 

+Locating Earthquakes

http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

+Locating Earthquakes

http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM

+Locating Earthquakes

http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM