Download Earthquakes

Bell Work 12/5/14
On your desk:
1. P.R.I.D.E card
1. How do you get a spaghetti noodle to bend
2. I.N.
and not break?
3. Pencil/Pen
2. How do you break a spaghetti noodle? 4. Summary 
3. How can you apply this concept to the
lithosphere?
Earthquakes
Earthquakes
 Earthquake- a
movement of Earth’s
lithosphere (rigid solid)
that occurs when rocks
in the lithosphere
suddenly shift, releasing
stored energy!
They’re Caused by a Build-up of
STRESS in Earth’s Crust
 As tectonic plates move, they cause stress in the crust,
which in turn produces folds and faults.
Stress in Earth’s Crust
 Stress (in earthquake terms) a force that squeezes rocks
together, stretches or pulls them
apart, or pushes them in different
directions.
 Does stress occur at…
 Convergent plate boundaries?
 Divergent plate boundaries?
 Transform boundaries?
Stress = Folds and Faults!
Folds=Plastic Deformation
 A bend in layers of
rock in response to
stress
 Form where rocks
are squeezed
together, but do
not break
 This doesn’t lead
to earthquakes
Faults
 Faults A fracture, or break,
in Earth’s
lithosphere
 Blocks of rocks
move (scrape) past
each other
 San Andreas Fault
Where do earthquakes occur??
 Most earthquakes happen along plate boundaries
 Ring of Fire- belt around the Pacific plate
 Over 75% of all earthquakes occur here
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Why Exactly do Earthquakes Happen?
 Elastic Rebound-The sudden return of elastically
deformed rock to its original shape
 Elastic rebound occurs when more stress is applied to
rock than the rock can withstand.
 During elastic rebound, energy is released as an earthquake
How do we measure
earthquakes?
2 different scales
 Seismic waves vs destruction!
Measuring Earthquakes
 Modified Mercalli scale- Rates
earthquakes based on observations of the
intensity of ground shaking and damage
Modified Mercalli Scale
San Francisco
earthquake of
1906 was an 11
Measuring Earthquakes
 Richter scale- Rates earthquakes
based on measurements of the times
and amplitudes of the seismic waves
 Created by Charles Richter in the 1930’s
How exactly do we Measure
earthquakes?
 To measure earthquakes and
pinpoint their epicenters,
geologists record seismic
waves using seismographs
 Seismograph a device that can detect and
record seismic waves
 Creates a seismogram
What is a Seismogram?
 Seismogram A tracing of earthquake motion created by a seismograph
Seismic Waves – the reason earthquakes are Dangerous!
 Seismic waves the energy
released during
an earthquake
carried by
vibrations
 3 main types:
 P waves
 S waves
 Surface waves
Seismic Waves
 P waves (primary waves)- longitudinal waves
similar to sound waves
 Move through solid and liquid material
 Compress and expand the ground
 Similar to an accordion or a slinky
Seismic Waves
 S waves (secondary waves)- Transverse
waves, like light.
 They cannot travel through liquids
S waves can’t pass through liquid…this is
why we know the outer core is a liquid!
Seismic Waves
 Surface Waves- develop when seismic waves reach
Earth’s surface
 Move more slowly than P and S waves
 Produce larger movements
 Create greater damage
Where do Earthquakes Happen?
 Earthquakes- occur because stress forces have
exceeded the strength of rock.
 Focus- the location beneath Earth’s surface where an
earthquake begins.
 Epicenter- the location on Earth’s surface directly
above the focus.
The S-P time method…
 How it’s used:
 Collect several
seismograms from
different seismographs
(at different locations)
 Plot seismograms on a
distance-time graph
 Draw circles around the
locations based on the
distance-time graph
 At the point where 3
lines intersect is the
earthquake 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
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