Earthquake
Let’s shake, rattle and roll
Earthquake
Basics
• Earthquake – shaking of
Earth’s crust caused by the
sudden release of energy
• Energy build over time until
stresses break the rocks
• Happen ~ every 30 seconds
• ~3,000 annually strong
enough to move sections of
Earth’s crust
• ~20 annually cause severe
damage
• Can only occur in the rigid
crust!
World Seismicity
U.S. Seismicity
Seismic Activity in the West
Causes
•
Elastic Rebound Theory –
1. Pressure and stress begin to build
along plate or fault boundaries
2. Pressure causes deformation and
shape changes in rock
3. Stress becomes great enough to
overcome friction
4. Plate or fault suddenly move
5. Plate or fault snap back to previous
shape
Elastic Rebound Theory
Elastic Rebound Theory Real Life
Earthquake Definitions
• Focus or
Hypocenter
• Epicenter
• Fault
• The point on the fault plane at
which the first movement of
the earthquake occurs
• The point on the earth’s
surface directly above the
focus of the earthquake
• A break or crack in the earth’s
crust from which movement
occurs.
Seismic
Waves
• Travel & act much like sound
waves
• 2 basic types
• Body Waves (2 types)
– Compressional, Primary or P wave
– Shear, Secondary or S wave
• Surface waves (2 types)
• Product of P & S waves reaching
the surface
– Love or L Waves
– Rayleigh waves
P Waves • Fastest traveler
• 1st to be recorded
• Travel through all materials
(rock, fluids, air)
• Move straight along ground
in an accordion fashion like a
spring or slinky
S Wave
• 2nd fastest wave
• Travels ~1/2 speed of P wave
• Particles move at right angles
to the direction of travel
• Only move in solids
• Cannot move in fluids or air
Love Waves
• Slower than both P & S
waves
• Travel like ripples in a
pond
• Very destructive!!!
Time Travel Graph
• A time travel
graph is used to
find the distance
to the epicenter.
Do Earth quake lab #1
• Finding the distance to the epicenter.
Locating an Earthquake
The Basics of Seismic
Exploration
1.
2.
3.
seismograph- instrument used to measure Earth’s
movements.
The pattern of seismic waves produced by a
seismograph = seismogram
Richter Scale- measures earthquake’s magnitude
(size of earthquake/amount of seismic waves)
Missoula
San Francisco
Denver
Guide to reading a seismogram
Use the data from the recording stations:

Station A: San Francisco, California
P-Wave arrival 3:02:20
S-Wave arrival 3:06:30
What is the time
difference
between P and
S wave arrivals?
Use the data from the recording
stations:

Station B: Denver, Colorado
P-Wave arrival 3:01:40
S-Wave arrival 3:05:00
What is the time
difference
between P and
S wave arrivals?
Use the data from the recording
stations:

Station C: Missoula, Montana
P-Wave arrival 3:01:00
S-Wave arrival 3:03:00
What is the time
difference
between P and
S wave arrivals?
Difference in arrival times:
San Francisco: 4:10
Denver, Colorado: 3:20
Missoula, Montana: 2:00
MOVE THE PAPER UNTIL THE TWO
TICK MARKS LINE UP WITH THE P
AND S CURVES
WHEN TICK MARKS LINE UP, GO
STRAIGHT DOWN AND READ THE
EPICENTER DISTANCE
EPICENTER DISTANCE
OF 2800 KM
Recording Board
Difference in arrival times:
San Francisco: 4:10
=2,800km
5,000
4,000
3,000
2,000
1,000
Open your compass to
the EXACT distance on
the scale.
EPICENTER DISTANCES
San Francisco: 4:10
2,800km
Denver, Colorado: 3:20
2,000km
Missoula, Montana 2:00
1,100km
.
2,800km
.
.
2,000km
Triangulation
How are the Size and Strength of an Earthquake Measured?
•
Magnitude
– Richter scale
measures total amount
of energy released by
an earthquake;
independent of
intensity
– Amplitude of the
largest wave produced
by an event is
corrected for distance
and assigned a value
on an open-ended
logarithmic scale
Site #1
Dist = 300km
Amp = 50mm
Site #2
Dist = 600km
Amp = 5mm
Site #3
Dist =100km
Amp = 500mm
Hand out Lab packet.. :O)