Earthquakes &
Earth’s Interior
Chapter 8 pg 217
Bill Nye on Earthquakes

http://www.youtube.com/watch?v=RwDEysDCsoM
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
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
e. Epicenter – place on surface
directly above focus
f. Faults and change to earth’s
surface
1) Vertical movement
a) Known as uplifting
b) Fault scarp – sharp edge
ridge
2) Horizontal - displacement
Imperial fault - displacement
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)
e. Causes forces
farther up fault
resulting in more
slippage
f. Continues until
energy is released
and rock returns
to previous state
Elastic Rebound
Page 220 figure 4
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
Effects of initial
earthquake
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
B. Measuring Earthquakes
1.
Intro
a. Seismology – study of
earthquake waves
b. Seismographs – record
earthquake waves
c. Seismogram – recorded ground
motion
Seismographs
Then
Now
2. Earthquake waves
a. Spread out in all directions
b. Surface waves
1) Travel along earth’s outer
layer
2) Up/down & side/side
motion
3) Most destructive waves
4) Change
volume of
material
temporarily by
pushing/pulling
5) Slowest waves
6) Recorded by
seismogram
c. Body waves
1) Travel through earth’s 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
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
3. Locating an Earthquake
a. Earthquake distance
1) Find time b/w 1st P wave
and 1st S wave
2) Use a travel-time graph
b. Earthquake Direction
1) Need 3 seismic stations
2) Circles are distance of
epicenter
3) Intersecting circles shows
epicenter
c. Earthquake zones
1) Circum-Pacific belt
a) Ring of fire
b) Outer edge of Pacific
Ocean
c) 75% of world’s earthquake
activity
d) Philippines, Japan, Chile,
Alaska
2) Mediterranean-Asian belt
3) Oceanic ridge system
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
Richter Scale
and
Magnitude
3) Only useful within 310 miles of
epicenter
4) Scientists no longer use it, but the
news does
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
4) Calculating:
a) Average amount of
movement along fault
b) Area of surface break
c) Strength of broken rock
C. Destruction from Earthquakes
Why does
one building
have almost
no damage
to it?
Factors
1.
a.
b.
c.
d.
Intensity
Duration
Material used in buildings
Building design
1)
2)
Wood and steel frames = more
flexible
Concrete needs to be
reinforced
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
2. Tsunamis
a. Causes
1) Ocean floor is displaced
vertically
2) Underwater landslide
b. Characteristics
1) Move quickly in open ocean
2) Can go unnoticed
3) Waves slow and increase in
size as depth decreases
c. Warning system
1) Use water levels in tidal
gauges
2) Provides about 1 hour
warning
Importance
http://www.youtube.com/watch?v=noq8FYvRqgs
3. Other dangers
a. Landslides
1) Most damage
2) Landslides, slopes fail,
ground collapses, gas and
water lines break
b. Fire
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) Hasn’t been successful
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
D. Earth’s Layered Structure
Intro
1.
a.
b.
We have only drilled 7.5 miles
How do we know what the inside
looks like?
- Studying earthquake
waves
c. Waves speed up with depth b/c
of pressure
d. Pressure causes waves to refract
2. Layers by composition
a. Crust
1) Oceanic
a) 7 km (4mi)
b) Igneous rocks (basalt)
c) Younger than
continental rocks
d) Ave. density 3.0
g/cm3
2) Continental
a) 8 – 75 km (5-47mi)
b) Average 40 km
c) Older than oceanic crust
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
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
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
4. Discovering layers
a. Finding crust/mantle
1) Moho discontinuity –
place where seismic waves
speed up
2) Named after Andrija
Mohorovicic
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 can’t go through
liquid
S waves
don’t go
through
core
E. Earthquake Safety
Before
1.
a.
b.
c.
Go over safety until it is instinctive
Teach everyone
Have emergency supplies
1)
2)
3)
4)
5)
Battery radio
Batteries
First aid kit
Water and food for 2 weeks
Blankets
d. Arrange home for safety
1) Heavy things on bottom shelf
2) Breakables with latched doors
3) Don’t 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)
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
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
e. If driving
1) Stop on side of road
2) Don’t stop under bridges and
overpasses, power lines, trees,
large signs
3) Stay in car
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
The New Madrid Fault
 https://www.youtube.com/watch?v=7kc7pJ8f1aY