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Have you been in an earthquake? What do you know about them? What do you think they would be like? What do you know about what you should
do in an earthquake? Describe your reaction to seeing the
videos.
EarthquakesWhat are they?
What causes them?
Are all the waves the same?
Why do some cause more
damage than others?
Intro to Earthquakes
Videos: https://www.youtube.com/watch?v=4Y-62Ti5_
6s http
://www.youtube.com/watch?v=tjNImLAJrTE
What exactly is an earthquake?
The shaking or trembling caused by the sudden release of energy
Usually associated with faulting or breaking of rocks
Continuing adjustment of position results in aftershocks
Where it starts…
Earthquake focus Focus – the point in Earth’s interior where the
energy waves are produced Epicenter
The point on Earth’s surface directly above the earthquake focus
San Andreas Fault in
California
What’s under there? Deep inside the earth, where temperatures are
very high, the heated rocky material is flexible, so it moves slowly and steadily.
Nearer the earth's surface, however, the rocky material becomes cooler and more brittle, and it cannot move so easily.
The slow, continual movement of material deep in the interior builds up and exerts stronger and stronger forces on the brittle rocks near the surface, making them move as well.
For an earthquake to occur, the rocks nearer the surface have to break suddenly — just like a stick that breaks suddenly when it is bent too far.
Layers of the Earth
Layers of Earth Crust: The first layer consists of about 10
miles (16km) of rock and loose materials scientists call the crust. Underneath the continents, the crust is almost three times as thick as it is under the oceans.
Mantle: Traveling beyond the Earth’s crust, we next encounter the mantle. The mantle extends to a depth of approximately 1,800 miles (2897km), and is made of a thick, solid, rocky substance that represents about 85% of the total weight and mass of the Earth.
Layers of Earth Outer Core: Traveling still deeper within the Earth, we
next would encounter the Earth’s outer core, which extends to a depth of around 3000 mile (4828km) beneath the surface. It is believed that this outer core is made up of super-heated liquid molten lava. This lava is believed to be mostly iron and nickel.
Inner Core: Finally, we would reach the Earth’s inner core. The inner core extends another 900 miles (1448km) toward the center of the Earth. It is believed that this inner core is a solid ball of mostly iron and nickel.
Crust, Mantle, Outer Core, Inner Core
What is the Elastic Rebound Theory?
Explains how energy is stored in rocks Rocks bend until the
strength of the rock is exceeded (snapping of a twig)
Energy is released in waves that radiate outward from the fault
Here is an orchard after an earthquake. Notice how the rows of trees have shifted.
Railroad tracks buckled in the earthquake in Alaska in 1964.
Body Waves: P and S waves
Body Waves: P and S waves Body waves
P or primary waves fastest waves travel through
everything (water, air, and ground)
compression wave, material movement is in the same direction as wave movement (inch worm)
S or secondary waves slower than P waves travel through solids
only shear waves - move
material perpendicular to wave movement
Types of Seismic Waves: Surface Waves Surface waves
Energy waves that reach the Earth’s surfaceEnergy waves that move rocks along the
surface of the Earth or in an elliptical motionThese waves cause the most damage.
Surface Waves: R and L waves
Surface Waves Travel just below or along the ground’s surface Slower than body waves; rolling and side-to-side movement Love waves (side to side motion) is particularly damaging to the
foundation of buildings but have little to no effect on water. Buildings are designed to stand up and resist gravity, a vertical
acceleration; however, the horizontal components of shaking can cause more damage.
Rayleigh waves (both horizontal and vertical movement), elliptical movement like waves in the ocean, can affect bodies of water.
Measuring Earthquakes
Earthquake Magnitude Usually determines the strength of the break Doesn’t determine the duration or the size For each increase of 1 is 10 times stronger
An earthquake of 4 is 10 times stronger than an earthquake of 3
Measuring Earthquakes Seismology
Seismologists - People who study earthquakes and seismic waves
Use instruments called seismographsRecord seismic wavesA drum with a sheet of paper
vibrates and a stationary pen marks the vibrations on the paper
The height of the lines are used to measure the energy released from the earthquake called the magnitude
Mercalli Scale Invented by Giuseppe Mercalli in 1902. Uses observations of people to estimate
its intensity Not considered scientific due to
exaggeration and the damage caused can vary greatly due to Building design Distance from the epicenter Type of surface material
Locating an Epicenter
Seismic waves do not travel through earth’s surface at the same speed Primary waves are the fastest Surface waves are the slowest
Seismograph stations Record the information from the earthquake
by recording the different types of waves as they reach the station
Locating an Epicenter
Epicenter Location If information is received from the earthquake
at three stations, then the epicenter can be located
A circle is drawn around each station on a mapThe radius is equal to the distance from the
station to the epicenter The point in which all three circles intersect is
the earthquake epicenter
How is an Earthquake’s Epicenter Located? Seismic wave behavior
P waves arrive first, then S waves, then L and R Average speeds for all these waves is known After an earthquake, the difference in arrival times at a
seismograph station can be used to calculate the distance from the seismograph to the epicenter.
Effects on Buildings
Northern Chile, 2005
What are the Destructive Effects of Earthquakes? Ground Shaking
amplitude, duration, and damage increases in poorly consolidated rocks
Tsunamis
Caused by the movement of the ocean floor Causes a disruption in the water Some are so wide that a large ship can travel
over the wave without knowing Recent earthquake in the Indian Ocean
created a tsunamis that was 100 feet high and moving at 500 mph
An elementary school caught in a landslide caused by the earthquake in Anchorage Alaska in 1964.
Who should pay for earthquake preparation?
Seismic safe structures Structures that are resistant to the vibrations
of Earth’s crust Structures are made with moorings
Made of steel and are filled with alternating layers of rubber and steel
These structures absorb the energy produced from the earthquake
Earthquake Safety
Quake proofing your home Place heavy objects near the floor Fix gas appliances in place