ObjectivesIdentify causes of earthquakesDistinguish between S waves, P
waves, and surface wavesDescribe how earthquakes are
measured and ratedTriangulate to find the location of an
earthquakeDiscuss the types of damage that
can occur
What are earthquakes?
Earthquakes are vibrations caused by movement of rocks sliding past each other.
Where are they most common? These movements
of rocks are more common at plate boundaries
California and Japan have many earthquakes because they are on plate boundaries.
Top 10 since 1900…Rank Date Location Magnitude Estimated Deaths/Damages (USD)
1 1960 Chile 9.5 1,655/$6 million 2 1964 Alaska 9.2 128/$300 million
3 2004 W. Sumatra 9.1 227,898/estimated in the billions
4 1952 Russia 9.1 none reported/$1 million
5 1906 Ecuador 8.8 500-1500/unknown
6 1965 Alaska 8.7 none reported/$10,000
7 2005 N. Sumatra 8.6 1300/unknown8 1950 Tibet 8.6 780/$25 million
9 1957 Alaska 8.6 none reported/$5 million
10 2007 S. Sumatra 8.5 21/unknown
Where will Haiti fit in?
In terms of magnitude it won’t be in the top 10
Magnitude 7.0
In terms of destruction and loss of life it will
Already 80,000 buried in mass graves
The number dead may reach over 200,000
Earthquake motion
Since the earth’s surface is in motion, rocks in the lithosphere sometimes slip past each other
Well maybe slip isn’t a good word for this, maybe they GRIND past each other
This Grinding caused shock waves that move through the earth
The ground can move in different directions…
They can move
sideways
They can move up and down
They can push up a
section
They can not break the surface
Earthquakes occur where the ground was Stuck
The forces build up until the
fault breaks – releasing
energy
Some terms
The focus is where the earthquake occurs
The fault is the plane that the earth slides along
The epicenter is the point on the surface above the focus – it might not be on the fault
Orders of Magnitude – The Richter scale
Not all earthquakes are the same
At magnitude 6, the ground moves 1 meter at the focus
At magnitude 7, the ground moves 10 meters
P waves
Called Primary or Longitudinal waves
Compress and release Travel fastest Can travel through earth’s core but do bend (refract)
S-waves
Secondary or Transverse waves
Move up and down (S shaped)
Do not travel through earth’s core
Surface Waves
Rolling up/down or right/left Occur on surface – like ocean waves Are the most destructive
Distance to an earthquake
Found by looking at time between P waves and S waves reaching the seismograph
Calculations tell you the distance to the focus
It takes three seismographic measurements to triangulate where the earthquake is located
What are the dangers
Buildings collapseHaiti
Roads break up1989 Loma Prieta
Earthquake, San Fransisco
Land can rise or sink
1964 Alaska, some land rose 40 feet, some seafloor dropped 50 feet
Liquefaction Softer rock does not stay
together, landfill is some of the worst land to build on
Landslides1692 the town of Port Royal,
Jamaica slide into the ocean, it landed 50 feet below sea level
TsunamisDecember 26, 2004
Earthquake
Buildings split Land can “boil”
Tsunamigenesis
The farther away you are, the longer it takes for the tsunami to reach you, you have more time to react