Journal  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.

Earthquakes What are they? What causes them? Are all the waves the same? Why do some cause more damage than others?

Intro to Earthquakes  Videos:  62Ti5_6s 62Ti5_6s 62Ti5_6s  E E E

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 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 surface  Energy waves that move rocks along the surface of the Earth or in an elliptical motion  These 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 seismographs  Record seismic waves  A 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  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 map  The 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 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