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.

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