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 Ridgeshttp://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 UShas 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 beneaththe 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