Haiti Earthquake
http://www.youtube.com/watch?v=fahz97JjeJ8&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 Earthquake1.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 Minor damage (felt by everyone)
800/year
4-4.9 Not felt by everyone 6,000/year
< 3.9 Very small 1 million/year
Largest Earthquake on the Richter Scale:
9.5Chile
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 Earthquake2. 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 Earthquakes1. 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 EarthquakesSeveral 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 WavesAs 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 WavesP - Waves
Primary Waves
- ‘pressure’ or ‘push – pull’ waves
- Travel fastest (few km/sec)
- Travel through all layers of Earth
Body WavesS – Waves
Secondary Waves
- ‘shear’ or ‘shape’ waves
- Travel slightly slower than P waves
- Do not travel through liquids (outer core)
Body Waves
Surface WavesR - Waves
Rayleigh Waves
- Make the ground ripple up and down
Surface WavesL - Waves
Love Waves
- Make the ground ripple side to side
Seismograph
http://snowball.millersville.edu/
~cws/seismic/current/Local_East-West/current.gif
An instrument that can record ground motion from an earthquake happening
anywhere on Earth
Locating an EarthquakeFocus
Spot in the crust where the fault begins to slip
*the deeper an earthquake, the less damage it causes at
the surface*
EpicenterPoint 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
TriangulationWhen 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 DisplacementDepending on the fault, giant cracks in the Earth can form
Alaska 1964
Examples:
1964–Alaska– 12 m
1906–San Francisco– 7 m
2. LandslidesSoil 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
Earthquakes that occur near
oceans create massive waves which act as a wall of water
Seismic sea wave
Sumatra 2004
5. FireDestruction during an
earthquake can cause large fires
Tokyo - 1923San Francisco - 1906