Download earthquakes - Archway Chandler

EARTHQUAKES
I.
Forces in the Earth’s crust
a. Movement of the plates creates force
b. Force, or stress, adds energy to the rocks
i. Three types of stress
1. Tension – pulls on the crust
2. Compression – squeezes rock until it folds or breaks
3. Shearing – pushes a mass of rock in opposite directions till it breaks or
slips
c. Fault – a crack resulting within the Earth’s crust as a result of the stress, usually along a
plate boundary,
i. Three types of faults
1. normal – caused by tension
2. reverse (thrust) – caused by compression
3. strike-slip – caused by shearing
II.
Earthquakes – are the result of energy that is released when two blocks of earth suddenly slip
past each other. (have students press hands together firmly while also sliding them, when they
suddenly slip and move, that is similar to what happens in the earth)
a. Focus – the place within the Earth’s crust where the pressure was released in an
earthquake.
b. Epicenter – the point on the Earth’s surface directly above the focus of an earthquake
(Have students draw model from Sciencesaurus pg. 186
c. Seismic Waves – the energy released from an earthquake (earthquake waves)
i. Primary Waves (P Waves)
1. these waves stretch and compress and are fast
2. have a push/pull or back and forth motion (P=push/pull)
3. can move through solids and liquids
ii. Secondary Waves (S Waves)
1. these waves move land side to side and are slower than P Waves (S =
side to side)
2. only travel through solids, cannot travel through liquids
iii. Land Waves (L Waves) – also called surface waves
1. these waves form when P and S Waves combine
2. they move land up and down (like ripples in a pond)
3. these waves travel on the Earth’s surface and are the most destructive
d. Richter Scale – tool used to measure the magnitude of an earthquake. It is based on the
energy released and measured on a scale of 1-9. Show students Richter scale in
Sciencesaurus pg. 186.
e. Magnitude – the strength of an earthquake as measured by a seismograph. It
corresponds to how much energy is released.
f. Mercalli Scale – scale used to rank earthquakes by how much damage they do