Transcript ch-8-ppt-notes - Cobb Learning

Chapter 8 Earthquakes

About 3 million earthquakes w/1+ magnitude
occur every year—about 1 every 10 seconds!
Highest recorded: 9.5 on the Richter scale in
Chile in 1960!
Seismology: study of earthquakes

The majority of quakes occur: in earthquake
zones where a large # of faults are located
along tectonic plates
What causes earthquakes?
 deformation:
change in shape of rock in
response to stress
-elastic deformation: rocks are
stretched & break releasing energy
which leads to an earthquake
-elastic rebound: sudden return of
elastically deformed rock to its original
shape (This is the CAUSE OF AN
EARTHQUAKE)
Plate Motion at
Tectonic Boundaries
Major Fault Type
Transform boundary
Strike-slip Fault
Convergent boundary
Reverse Fault
Divergent boundary
Normal Fault
BODY WAVE
BODY WAVE
SURFACE WAVE
P Waves
(pressure waves)
S Waves
(shear waves)
Surface Waves
-AKA
-AKA
secondary waves
primary waves
-travel thru
-don’t travel thru
solids, liquid, & gas liquids
-travel:
affect upper few
kilometers of Earth’s
surface
-fastest &
1st detected
-speed:
travel slowly
-2nd fastest
-most destructive
-moves:
back & forth
(squeezed &
-moves:
side to side
-1st type moves: up
& down, around
-2nd type moves:
Locating Earthquakes
epicenter: point on surface
above quake’s starting point
focus: point inside Earth where a
quake begins
Determining Time & Location of Quakes
S-P Time Method—used to find epicenter
Step 1: collect several seismograms from same
quake from different locations
Step 2: place seismograms on a time-distance
graph
Step 3: line up the first P-wave seismogram
tracing w/the P-wave time-distance curve
Step 4: line up the first S-wave tracing w/S-wave
time-distance curve
Step 5: find distance of each station from quake by
reading horizontal axis on graph
Step 6: after finding distances, can locate the
quake’s epicenter.
Locating Earthquakes
seismographs: instrument at or near
Earth’s surface that records
seismic waves on a seismogram
seismogram: tracing of quake motion
Measuring Quake Strength & Intensity
magnitude: measure of strength of
quake
The Richter Scale: scale that measures
ground motion from quake & adjusts
for distance to find its strength
intensity: measure of degree a quake is
felt & amount of damage caused—use
the Modified Mercalli scale
Magnitude
2.0
3.0
Estimated Effects
Only detected by
seismograph
Felt at epicenter
4.0
Felt by people in area
5.0
Damage at epicenter
6.0
Widespread damage
7.0
Great, widespread
damage
Modified Mercalli Intensity Scale
numerical scale from I-XII--describes
increasing quake intensity levels
Level I-----not felt by most people
to
Level XII-----total damage of an area
Earthquakes and Society
Predicting when, where, & at what
strength earthquakes will occur is
difficult.
Earthquake Hazard: measurement of
how likely an area is to have damaging
future quakes
To decrease earthquake damage, buildings,
homes, and bridges can be strengthened to
decrease damage.
 technology sensors in roof that control
building shift to counteract movement
 steel cross braces
 flexible pipes
 base isolators to absorb wave energy
Safeguard homes-in addition to
strengthening house, heavier objects on floor
Earthquakes and Buildings
Retrofitting: making older buildings quake
resistant
New technology for earthquake
resistant buildings
-mass damper: motion sensors in roof that detects
movement & send messages to a computer which
signals controls in roof to shift the mass damper to
counteract the building movement
-steel cross braces: braces between floors to
counteract pressure that pushes & pulls at side of
building during quake
-active tendon system: sensors in roof that indicate
the building is moving
-flexible pipes: pipes w/flexible joints that twist &
bend w/out breaking
-base isolators: layers of rubber & steel wrapped
around a lead core that absorb waves & prevent
them from traveling thru buildings
Preparing for an Earthquake
Before an earthquake:
1. safeguard your home (heavier objects on
bottom shelves
2. if possible, strengthen your home
3. find safe places w/in each room
4. make a plan to meet in a safe place
5. store water, food, fire extinguisher, flashlight,
batteries, radio, medicine, & first-aid kits
When the shaking starts:
1. if indoors, lie face down under a table
2. if outdoors, lie face down away from danger
3. if in a car, stop, remain inside
After the shaking stops:
1. stay calm & get your bearings
2. remove yourself from danger
3. go home if told it is safe
4. beware of aftershocks & more damage