Earthquakes & Earth’s Interior Chapter 8 pg 217. Bill Nye on Earthquakes
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- Earthquakes & Earths Interior Chapter 8 pg 217
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- Bill Nye on Earthquakes
http://www.youtube.com/watch?v=RwDEysDCsoM
http://www.youtube.com/watch?v=RwDEysDCsoM
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- A. What is an Earthquake? 1. Earthquakes a. A vibration of
Earth produced by rapid release of energy within the lithosphere b.
Happen along a fault c. Fault fracture in the crust where movement
occurs
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- d. Focus 1) Place where earthquake starts 2) Along a fault
beneath surface 3) Energy goes out in all directions 4) Energy
travels as seismic waves
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- e. Epicenter place on surface directly above focus
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- f. Faults and change to earths surface 1) Vertical movement a)
Known as uplifting b) Fault scarp sharp edge ridge 2) Horizontal -
displacement
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- Imperial fault - displacement
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- 2. Cause of Earthquakes (Elastic rebound hypothesis) a.
Convection currents move plates on both sides of fault b. Rocks
bend and store elastic energy c. Resistance from friction is
overcome d. Rocks slip at weakest point (fault)
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- e. Causes forces farther up fault resulting in more slippage f.
Continues until energy is released and rock returns to previous
state
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- Elastic Rebound Page 220 figure 4
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- g. Aftershocks 1) Smaller than original quake 2) Happen after
original quake 3) Caused from additional movements along the fault
4) Cause damage to previously weakened buildings
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- Effects of initial earthquake
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- h. Foreshocks small quakes before large earthquake i. Fault
segments behave differently 1) Fault creep slow gradual movements
2) Regular slippage 3) Stay locked for extended periods of
time
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- B. Measuring Earthquakes 1. Intro a. Seismology study of
earthquake waves b. Seismographs record earthquake waves c.
Seismogram recorded ground motion
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- Seismographs ThenNow
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- 2. Earthquake waves a. Spread out in all directions b. Surface
waves 1) Travel along earths outer layer 2) Up/down & side/side
motion 3) Most destructive waves
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- 4) Change volume of material temporarily by pushing/pulling 5)
Slowest waves 6) Recorded by seismogram
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- c. Body waves 1) Travel through earths interior 2) P waves a)
Push-pull waves (compress/expand) b) Push/pull rocks in direction
wave travels c) Known as compression waves d) Fastest waves
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- 3) S waves a) Shake particles at right angles to their
direction of travel b) Transverse waves c) Change shape of material
they pass through temporarily d) Gases and liquids will not
transmit them b/c there is no elastic rebound to original
shape
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- 3. Locating an Earthquake a. Earthquake distance 1) Find time
b/w 1 st P wave and 1 st S wave 2) Use a travel-time graph
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- b. Earthquake Direction 1) Need 3 seismic stations 2) Circles
are distance of epicenter 3) Intersecting circles shows
epicenter
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- c. Earthquake zones 1) Circum-Pacific belt a) Ring of fire b)
Outer edge of Pacific Ocean c) 75% of worlds earthquake activity d)
Philippines, Japan, Chile, Alaska 2) Mediterranean-Asian belt 3)
Oceanic ridge system
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- 4. Measuring Earthquakes a. Intensity measures shaking based on
amount of damage b. Magnitude measures seismic waves c. Richter
Scale 1) Based on amplitude of largest seismic wave 2) Logarithmic
scale
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- Richter Scale and Magnitude
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- 3) Only useful within 310 miles of epicenter 4) Scientists no
longer use it, but the news does
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- d. Moment Magnitude 1) More accurate than Richter scale 2)
Based on amount of displacement along fault 3) Only scale that
estimates energy released by earthquakes
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- 4) Calculating: a) Average amount of movement along fault b)
Area of surface break c) Strength of broken rock
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- C. Destruction from Earthquakes Why does one building have
almost no damage to it?
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- 1. Factors a. Intensity b. Duration c. Material used in
buildings d. Building design
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- 1) Wood and steel frames = more flexible 2) Concrete needs to
be reinforced
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- e. Liquefaction 1) Happens to loosely packed saturated soils 2)
Soil turns into a liquid 3) Buildings settle, underground
structures rise http://www.youtube.com/watch?v=4Uwxr42JqYQ
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- 2. Tsunamis a. Causes 1) Ocean floor is displaced vertically 2)
Underwater landslide
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- b. Characteristics 1) Move quickly in open ocean 2) Can go
unnoticed 3) Waves slow and increase in size as depth
decreases
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- c. Warning system 1) Use water levels in tidal gauges 2)
Provides about 1 hour warning Importance
http://www.youtube.com/watch?v=noq8FYvRqgs
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- 3. Other dangers a. Landslides 1) Most damage 2) Landslides,
slopes fail, ground collapses, gas and water lines break b.
Fire
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- 4. Predicting Earthquakes a. Short-range 1) Study uplift,
strain in rocks, water levels, pressure in wells, radon gas
emission, electromagnetic properties in rocks 2) Hasnt been
successful
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- b. Long-range 1) Probability of certain magnitude earthquakes
happening w/in 30-100+ yrs 2) Important for building codes 3) Based
on that earthquakes are cyclical 4) Study seismic gap no activity
for long periods of time 5) Limited success
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- D. Earths Layered Structure 1. Intro a. We have only drilled
7.5 miles b. How do we know what the inside looks like? - Studying
earthquake waves
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- c. Waves speed up with depth b/c of pressure d. Pressure causes
waves to refract
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- 2. Layers by composition a. Crust 1) Oceanic a) 7 km (4mi) b)
Igneous rocks (basalt) c) Younger than continentalrocks d) Ave.
density 3.0 g/cm 3
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- 2) Continental a) 8 75 km (5-47mi) b) Average 40 km c) Older
than oceanic crust
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- b. Mantle 1) Middle layer 2) 1795 miles 3) Density 3.4g/cm3 c.
Core 1) Iron-nickel alloy 2) Density 13 g/cm3 3) 2162 miles
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- 3. Layers by physical properties 1) Lithosphere a) Rigid shell
b) Crust and upper mantle 2) Asthenosphere a) Upper mantle b) Rocks
near melting point c) Putty like substance
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- 3) Lower mantle a) More rigid but still can flow b) Bottom part
is much more fluid from heat from core 4) Outer core a) Liquid b)
Flowing causes magnetic field 5) Inner core solid from
pressure
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- 4. Discovering layers a. Finding crust/mantle 1) Moho
discontinuity place where seismic waves speed up 2) Named after
Andrija Mohorovicic
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- b. Finding outer core (fig 16 pg 236) 1) P waves bend around
liquid core 2) Shadow zone p waves arrive minutes slower than
expected through outer core 3) S waves cant go through liquid
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- S waves dont go through core
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- E. Earthquake Safety 1. Before a. Go over safety until it is
instinctive b. Teach everyone c. Have emergency supplies 1) Battery
radio 2) Batteries 3) First aid kit 4) Water and food for 2 weeks
5) Blankets
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- d. Arrange home for safety 1) Heavy things on bottom shelf 2)
Breakables with latched doors 3) Dont hang heavy things (mirrors,
pictures, etc.) above where people sleep 4) Anchor heavy appliances
5) Flammable liquids away from ignition sources (water heaters,
stoves, furnaces)
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- e. Locate main turn-offs (water, gas, and electric) 2. During
a. Stay inside b. Move: 1) Under desk or table 2) Interior wall 3)
NOT by windows, mirrors, fireplaces, and hanging objects
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- c. If cooking turn off stove and take cover d. If outside 1)
Move to open area 2) Get away from buildings, power lines, and
trees
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- e. If driving 1) Stop on side of road 2) Dont stop under
bridges and overpasses, power lines, trees, large signs 3) Stay in
car
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- 3. After a. Check for injuries b. Check for damage to see if
you are safe c. Smell gas open windows and get outside d. Smell/see
frayed wires turn off electric and get outside
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- The New Madrid Fault
https://www.youtube.com/watch?v=7kc7pJ8f1aY
https://www.youtube.com/watch?v=7kc7pJ8f1aY