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Earthquakes!

- Adapted from www.middleschoolscience.com

What is an earthquake?

- Used to describe both sudden slip on a fault, and

the resulting ground shaking and radiated seismic

energy caused by the slip - Caused by volcanic or magma activity,
- Caused by other sudden stress changes in the

earth.

Three Types of Faults

Strike-Slip

Thrust

Normal

What causes earthquakes?

- Tectonic plates move past each other causing

stress. Stress causes the rock to deform, break,

and/or move

Elastic Rebound deformed rock goes back to its

original shape

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

.HTM

Focus point inside the Earth where an

earthquake beginsEpicenter point on Earths

surface above focus

How Seismographs Work

Its a weighted pen writing on a rolling drum of

paper.

the pendulum remains fixed as the ground moves

beneath it

this mass, like the pen, has inertia and so

resists motion.

Normally everything would move, but.

Typical Seismogram

http//isu.indstate.edu/jspeer/EarthSky/EarthCh11

.ppt

Primary Waves (P Waves)

- PUSH-PULL PATTERN!
- A type of seismic wave that pushes pulls the

ground - The FIRST wave to arrive from an

earthquaketravels the fastest! - Travels Parallel to the direction the wave travels

http//daphne.meccahosting.com/a0000e89/insideear

th2.htm

Secondary Waves (S Waves)

- A type of seismic wave that moves the ground up

and down or side-to-side (perpendicular) to the

direction the wave travels - Slower!
- More destructive
- to buildings

http//daphne.meccahosting.com/a0000e89/insideear

th2.htm

(No Transcript)

Comparing Seismic Waves

P S Wave song http//www.youtube.com/watch?v

w3NLexYxR7g

Surface Waves

- Move along the Earths surface
- ROLL OUT! Motion can be up and down, around

back forth - Travel more slowly than S and P waves
- Last to arrive
- Most destructive to structures

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 difference between the arrivals of the P

waves and the S waves

Locating Earthquakes

Question Where could the EQ be?

- Find the difference in the arrival times, or lag

time ( t ), of the P S waves.

3. Use the distance from the EQ as the radius (r)

for this circle.

r

?Difference in arrival times?

P-wave

S-wave

2. Find the distance to the EQ using the lag time

and this Time/Distance graph.

Time ( t)

Answer Anywhere along the blue line. (not much

help)

Distance (km)

Locating Earthquakes

Question Where could the EQ be, now?

Lets get someone else that has readings for

this EQ to help out (Same procedure)

?Difference in arrival time?

\?Arrival diff.?\

Answer Where the green and blue circles

cross. (Better, but still a 50-50 change of going

to the right place to find the EQ.)

Locating Earthquakes

So, no more guessing Question where is the

actual EQ ?

If you get 3 people working on this puzzle, now

you can triangulate.

?Difference in arrival time?

\?Arrival diff.?\

\?Arrival time diff. ?\

Answer Where all 3 circles intersect

How are Earthquakes Measured? Richter

Scale-measures energy

How are Earthquakes Measured? Mercalli

Scale-measures damage

Click Link for Interactive Demo

http//elearning.niu.edu/simulations/images/S_port

folio/Mercalli/Mercalli_Scale.swf

Earthquake Waves Earths Interior

See how seismic waves move through the Earths

layers here (Shadow zone) http//www.classzone.co

m/books/earth_science/terc/content/visualizations/

es1009/es1009page01.cfm

Seismic Waves in the Earth

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

.HTM

Tsunamis

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

.HTM

Formation of a tsunami

http//isu.indstate.edu/jspeer/EarthSky/EarthCh11

.ppt

Tsunami Warning System

http//isu.indstate.edu/jspeer/EarthSky/EarthCh11

.ppt