Earthquakes
What Is An Earthquake? Click here to find out
What is an earthquake?
• Used to describe both sudden slip on a fault, and the resulting
ground shaking and radiated seismic energy caused by the slip
• Caused by volcanic or plate activity,
http://eqseis.geosc.psu.edu
The map above shows the distribution of earthquakes with magnitudes greater
than 5.0 that occurred between 1965 and 1995.
Three Types of Faults
Strike-Slip
Animation of fault movement
Reverse
Normal
Normal fault
Pulls on the crust stretching rock so that it becomes thinner (like pulling
on bubble gum) =
Occurs when plates are moving apart
Hanging wall
Foot wall
Results in hanging wall slipping downward
animation
What type of fault?
normal
Hanging wall
Foot wall
http://www.bgs.ac.uk/eqr/GeoD_Structures.htm
What causes earthquakes?
• Tectonic plates move past each other causing
stress. Stress causes the rock to deform
– What type of fault boundary is this? transform
– What type of stress is shown? shearing
Strike – slip fault
Rocks on either side of fault slip past each other sideways with little
up or down motion What type of stress is produced?
Occurs at a transform plate boundary
Animation of strike-slip motion
Fault rupture across road in western Kaynasli, right-lateral strike slip displacement was
about 4.0 m (13 feet) at this location
http://www.geerassociation.org/GEER_Post%20EQ%2
0Reports/Duzce_1999/kaynasli1.htm
Reverse fault
Pushes on the crust squeezing rock until it folds or breaks (like a trash
compactor) =
Occurs when plates are moving together
Hanging wall
Foot wall
Results in hanging wall slipping upward
animation
What type of fault?
reverse
Hanging wall
Foot wall
http://geologicalintroduction.baffl.co.uk
What type of fault?
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Focus – 1. point inside the Earth where an
earthquake begins
Epicenter – 2. point on Earth’s surface above focus where
earthquake is FELT most strongly
2
1
How Seismographs Work
A seismograph is an instrument used for recording the intensity and
duration of an earthquake.
the pendulum remains
fixed as the ground
moves beneath it
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Earthquakes
• How are earthquakes measured?
Seismogram –
seismic wave
display record
Seismograph
machine
Seismic Waves
Primary Waves (P Waves)
• A type of seismic wave that compresses
and expands the ground
• The first wave to arrive at an
earthquake
http://daphne.meccahosting.com/~a0000e89/insideearth2.htm
Secondary Waves (S Waves)
• A type of seismic wave that moves the
ground up and down or side to side
http://daphne.meccahosting.com/~a0000e89/insideearth2.htm
Comparing Seismic Waves
Surface Waves
• Move along the Earth’s surface
• Produces motion in the upper crust
– Motion can be up and down
– Motion can be around
– Motion can be back and forth
• Travel more slowly than S and P waves
• More destructive
Animation of wave types
How do scientists calculate how far a location is
from the epicenter of an earthquake?
• Scientists calculate the difference
between arrival times of the P waves
and S waves
• The further away an earthquake is, the
greater the time between the arrival of
the P waves and the S waves
Typical Seismogram
How much time elapsed between the arrival of the
P wave (start) and the arrival of the S wave (finish)?
start
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt
finish
Locating Earthquakes
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Locating Earthquakes
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Now you are going to be seismologists
and locate an Earthquake
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Go to: http://tinyurl.com/11quake13
Click here to go to virtual earthquake site
National Geographic earthquake information
How are Earthquakes Measured?
Richter Scale
A logarithmic scale
used to express the
total amount of
energy released
magnitude of an
___________
earthquake. Its
values typically fall
between 0 and 9,
with each increase
of 1 representing a
_________ increase
10-fold
in energy.
How are Earthquakes Measured?
Mercalli Intensity Scale
A scale of earthquake intensity based on ___________
observed effects
and ranging from I (detectable only with instruments) to
XII (causing almost total destruction).
Click for Interactive Demo
Go to http://tinyurl.com/13quake13
Earthquake Waves & Earth’s Interior
Seismic wave animation
Seismic
Waves in
the Earth
Click here for animation
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Tsunamis
Click here for explanation of a tsunami
http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
Formation of a tsunami
a large ocean wave usually caused by an underwater earthquake
or a volcanic explosion.
PBS –tsunami animation
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt
With typical waves, water flows in circles, but with a tsunami, water
flows straight. This is why tsunamis cause so much damage!
Click here for Japan helicopter view of tsunami
Tsunami Warning System
http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt
Review Questions
1. A large ocean wave usually caused by an
underwater earthquake or a volcanic explosion.
tsunami
2. Used to describe both a sudden slip on a fault,
and the resulting ground shaking and radiated
seismic energy caused by the slip
earthquake
How are Earthquakes Measured?
3. Which one uses a logarithmic scale to express the
total amount of energy released or magnitude of an
earthquake.
Richter Scale
4. Which uses a scale of earthquake intensity
based on observed effects and ranging from I
(detectable only with instruments) to XII (causing
almost total destruction).
Modified Mercalli Scale
What type of fault is shown by each picture?
1.
2.
Normal
Reverse
3.
Transverse
or strike-slip
S-wave
Surface or
Love waves
What type of fault?
Source: indiana.edu
http://geologicalintroduction.baffl.co.uk
A
Hanging wall has moved upward
Reverse fault
B
Strike –slip or
transverse fault
Focus – 1. point inside the Earth where an
earthquake begins
Epicenter – 2. point on Earth’s surface above focus where
earthquake is FELT most strongly
2
1
People walk along a damaged road in the province
of Bohol on Tuesday, October 15, 2013.
Do you think this was a major earthquake? Why or why not?
Yes, it was a major quake.
It crumbled a number of buildings
Such as this church
7.1 magnitude earthquake hit the Philippines
Earthquakes
3. Surface
1.
P-wave
2. S-wave
Seismogram
4. ____________
seismic wave
display record
5. Seismograph
__________
machine