Plate Tectonics and Earthquakes
Brittle vs. Ductile Deformation
Brittle
• Breaks when stressed
Ductile
• Bends when stressed
Brittle vs. Ductile Deformation
Deformation is dependent on:
1. Temperature (Cold or Hot)
2. Composition (Soft or Hard)
3. Strain Rate (Fast or Slow)
Brittle vs. Ductile Deformation
How does the Milky Bar deform when stressed?
a. What if we froze it?
b. What if we heated it?
Plate Tectonics
Plate Tectonics
•
•
•
•
Crust – Uppermost part of the Earth
Lithosphere – Crust and Upper Part of Mantle
Mantle
Core
Convection
Major Plates
• Major Plates
–
–
–
–
–
–
–
North American
South American
Eurasian
African
Pacific
Antarctic
Indoaustralian
• Others to note
• Juan de Fuca
• Nazca
• Arabian
• Caribbean
Types of Plate Boundaries
• Divergent (Tension)
– Mid-Ocean Ridges
• East Pacific Rise
• Mid-Atlantic Ridge
• Convergent (Compression)
– Subduction Zone
– Cascade Mountains
– Himalayan Mountains
• Transform (Shear)
– San Andreas Fault
Divergent Boundaries
• Mid Ocean Ridges
http://www.youtube.com/watch?v=t-ctk4KR-KU
Convergent Boundaries
• Subduction Zone – One Plate goes under the
other plate
Convergent Boundaries
• Subduction – Ocean/Continental – Andes
Transform Boundaries
• Shear motion
• Plates slide past each
other
• San Andreas Fault
Western US
has all three!
Earthquakes
• Occur on Faults
– a break in the rock of the crust where rock
surfaces slip past each other (displacement has
occurred)
• Measured on the Moment Magnitude Scale
– Logarithmic scale
• Change 1 magnitude - 32 times more energy
Earthquakes
Earthquakes
• Focus (hypocenter) the location inside the
earth where the first
rupture of the
earthquake took place
• Epicenter- the point on
the Earth’s surface that
is directly above the
focus (hypocenter)
Faults - Brittle
• Hanging Wall(Top)/Foot Wall(Bottom)
• Normal Faults
• Reverse Faults
– Thrust Faults
• Strike-Slip Faults
– Left and right lateral
Models of Faults
High Fives
Folds - Ductile
• Anticline – oldest rocks
in the middle
• Syncline – youngest
rocks in the middle
California Seismicity
http://earthquake.usgs.gov/earthquakes/recenteqscanv/
California Seismicity
Seismic Waves
Seismic Waves
Fold and Fault Model
• Compression!
• What types of faults will we see?
• What else do you see?
Earthquake Preparedness
• Have a pair of shoes next to the bed
– Due to broken glass from windows or other debris
• Create Post-Disaster Kit
– One at home and one in your car
• Drop, Cover, Hold On
– Do not run to the doorway, find something to get
underneath
• Don’t forget about aftershocks!
• K-12 Earthquake Lesson Plans
http://www.scec.org/education/k12/eclakit/index.html
Tsunamis
• A tsunami is a series of sea waves most
commonly caused by an earthquake beneath
the sea floor
• In the open ocean, tsunami waves travel at
speeds of up to 600 miles per hour
• The first wave is often not the largest
• Successive waves may be spaced many
minutes (up to 30-40 mins) apart and
continue arriving for a number of hours
Tsunamis
Tsunamis
• Since 1812, the California coast has had 15
tsunamis with wave heights higher than
three feet; seven of these were destructive
• The worst tsunami resulted from the 1964
Alaskan earthquake and caused 12 deaths and
at least $17 million in damages in northern
California (2011 tsunami’s damages have not been totaled yet)
What to do!
• If you feel a serious earthquake, and you are
near the shoreline:
• Get inland and up as soon as possible.
– 100 ft in elevation or higher
– 2 miles or more inland
• If the tide recedes, get away fast.
• Inform others to get to safety
Forces
• F=ma
• Force = mass * acceleration
• Units:
– N (Newtons) = kg * m/s2
– 1 Kilogram = 2.2 lbs
– 1 Meter = 3.28 feet = 100 cm = 1000 mm
– Gravity = 9.8 m/s2
Forces
• Forces have both magnitude (size) and
direction
• Unequal forces will cause a change in velocity
Forces
• Examples:
– Box on table (steady state)
– Box in hand (steady state)
– Box in hand (change in forces)
– Pushing a large box (static and kinetic friction)
– Tension
– Compression
Forces
• Examples:
– Strike-slip faults: Stick slip
• Forces and friction
– Normal faults:
• Tension
– Reverse faults:
• Compression