Download What is an Earthquake?

Haiti Earthquake
http://www.youtube.com/watch?v=fahz97JjeJ
8&feature=channel
Chile Earthquake
http://www.youtube.com/watch?v=T7jaayXlm
-M
chile ppt.ppt
What is an Earthquake?
A shake or vibration
caused by the
sudden breaking or
sliding of rock in the
Earth
Where do they happen?
Fault - Fracture (break) in rock where
sliding occurs
As tectonic plates move, they slide past other plates.
At the edges they get stuck, but the plates keep
moving.
Eventually, the rock gives and a fault is formed.
Elastic Rebound
Stress builds up between the
two plates causing the crust
to warp
An earthquake allows that
energy to be released, and
the plates return to their
normal position (just shifted)
Stages of an Earthquake
1.Inactivity
(1 ½. Foreshock small quake that can
occurs hours or days before a major
earthquake)
2. Major Earthquake
3. Aftershock quakes that occur seconds
to a year after a major earthquake
TYPES OF FAULTS
Normal Fault
Reverse Fault
Strike Slip
Normal Fault
-blocks of rock move apart
-occur at divergent boundaries
Reverse Fault
-blocks of rock move towards each
other
-occur at convergent boundaries
Strike Slip
-rocks move
sideways past
each other
-occur at
transform
boundaries
Earthquakes don’t always occur
along a plate boundary…
New Madrid Fault
1811-1812
3 Magnitude 8
Earthquakes
How do we measure earthquakes?
1.Richter Scale
-measures the height of seismic waves
-each whole number is 10 times the seismic
wave height
-each whole number is 33 times more
energy released
Richter Scale
>8
Total destruction
About 1/year
7-7.9
Bad
18/year
6-6.9
Moderate -serious
120/year
5-5.9
800/year
4-4.9
Minor damage (felt by
everyone)
Not felt by everyone
< 3.9
Very small
1 million/year
6,000/year
Largest Earthquake on the
Richter Scale:
9.5
Chile
1960
How do we measure earthquakes?
2. Mercalli Intensity Scale
-the amount of damage an earthquake
causes
-scale of I - XII
-very subjective
-typically used for building codes
Mercalli Scale
How do we measure earthquakes?
3. Moment Magnitude Scale
-combine how rigid the Earth is and
the distance the Earth moves along
the fault
-scientists use this method the most
Predicting an Earthquake
1.Short-term ‘Forecasting’
-hours to weeks
-based on foreshocks
*not always foreshocks
Predicting an Earthquake
2. Seismic Gap
-areas along faults that have not had
recent earthquakes
-the more time without an earthquake, the
greater the chance of an upcoming
earthquake
-larger earthquakes in the past -> more
frequent earthquakes
Predicting an Earthquake
3. Recurrence Interval
-earthquakes along a fault tend to have
relatively constant recurrence patterns
ex: San Andreas Fault
-22 years between earthquakes of
magnitude 5.5 or higher
Predicting an Earthquake
4. Anomalous Animal Behavior
-dogs barking
-chickens not laying eggs
-rats perched on power lines
*not considered scientific*
though often evident
Deadliest Earthquakes
1. Shaanxi, China 1556 -830,000 casualties
2. Tangshan, China 1976 – 255,000
casualties
3. Gansu, China 1920 – 234,117 casualties
4. Haiti 2010 -233,000 casualties
5. Indian Ocean (Sumatra) 2004 –
230,210 casualties
Tangshan, China
Animals also gave a warning that something was about
to happen. One thousand chickens in Baiguantuan
refused to eat and ran around excitedly chirping. Mice
and yellow weasels were seen running around looking
for a place to hide. In one household in the city of
Tangshan, a goldfish began jumping wildly in its bowl. At
2 a.m. on July 28, shortly before the earthquake struck,
the goldfish jumped out of its bowl. Once its owner had
returned him to his bowl, the goldfish continued to jump
out of its bowl until the earthquake hit.
Chen Yong, et al, The Great Tangshan Earthquake of 1976: An Anatomy of Disaster (New York: Pergamon Press, 1988) 53.
Human Induced Earthquakes
Several earthquakes have been
caused because of human activity
Examples:
-building dams over inactive fault zones
(e’quake and flooding)
- Nuclear Explosions (Nevada test site)
*Some scientists think we should trigger
‘controlled quakes’ in California to reduce
potential damage
Seismic Waves
As energy is released from an earthquake,
it is distributed in waves
Seismic Waves
Body Waves
Travel through the
interior of the Earth
Surface Waves
Travel along the Earth’s
surface
Body Waves
P - Waves
Primary Waves
- ‘pressure’ or ‘push – pull’ waves
- Travel fastest (few km/sec)
- Travel through all layers of Earth
Body Waves
S – Waves
Secondary Waves
- ‘shear’ or ‘shape’ waves
- Travel slightly slower than P waves
- Do not travel through liquids (outer core)
Body Waves
Surface Waves
R - Waves
Rayleigh Waves
- Make the ground ripple up and down
Surface Waves
L - Waves
Love Waves
- Make the ground ripple side to side
Seismograph
An instrument that can record ground
motion from an earthquake happening
anywhere on Earth
http://snowball.millersville.edu/~cws/se
ismic/current/Local_EastWest/current.gif
Locating an Earthquake
Focus
Spot in the crust where the
fault begins to slip
*the deeper an earthquake,
the less damage it causes at
the surface*
Epicenter
Point on Earth’s surface
directly above the focus
Locating an Earthquake
How to find an
epicenter
-need 3 seismic stations
to record the event
-using the differences in
arrival times,
seismologists can
determine the distance
of the station to the
epicenter
Triangulation
When you connect the data from the 3
seismic stations, you will find the
epicenter
Earthquake Aftermath
Earthquakes themselves cause
tremendous damage, but they
also leave behind a path of
destruction
1. Ground Displacement
Depending on the fault, giant
cracks in the Earth can form
Examples:
1964–Alaska– 12 m
1906–San Francisco– 7 m
Alaska 1964
2. Landslides
Soil and Debris
that is shaken
during an
earthquake
may loosen
and cause a
landslide
3. Liquefaction
Soil that has
small amounts
of water in it,
will act as a
liquid during an
earthquake
Ex: Kobe, Japan 1995
4. Tsunami
Seismic sea wave
Earthquakes that
occur near oceans
create massive
waves which act
as a wall of water
Sumatra 2004
5. Fire
Destruction during an earthquake
can cause large fires
Tokyo - 1923
San Francisco - 1906