EARTH SCIENCE EARTHQUAKES

The Earth seems so solid to us.

Scientists have found that the Earth is actually made up of different layers, each with their own composition and temperature.

The Earth’s top layer, the crust is divided into many large “plates” that shift and slide against each other.

These plates are constantly moving. Most of these movements are so slight that we are unaware of them.

However, sometimes plate movement can be sudden and be accompanied by a noticeable shaking of the ground.

This sudden movement is called a EARTHQUAKE!

Scientists estimate that over one million earthquakes occur each year. This is about one earthquake every 30 seconds!

Lab: A Whole Lot of Shaking Going On!

Earthquakes can occur anywhere in the world!

However, most earthquakes take place in regions called earthquake belts.

Scientists believe that these belts are located where the Earth’s plates come in contact with each other.

Earthquake Vocabulary Focus The underground point of origin of an earthquake.

Epicenter The point of land right above an earthquake’s focus.

Whenever an earthquake occurs, seismic waves spread out in all directions from the earthquake focus.

There are two types of SEISMIC BODY WAVES.

The seismic waves that travel the fastest are known as P, or primary waves. These waves cause rock particles to move forward and backward.

For this reason, some seismologists refer to P waves as push-pull waves.

S, or secondary waves cause rock particles to move side to side. Some seismologists refer to S waves as shear waves.

S waves travel slower from the focus than P waves.

Lab: Shake It Up!

There are two types of SEISMIC SURFACE WAVES.

Seismic Surface Waves It's the fastest surface wave and moves the ground from side-to-side.

The fastest surface wave and moves the ground up and down and side-to-side.

Most of the shaking felt from an earthquake is due to the Rayleigh wave, which can be much larger than the other waves.

Seismic Waves Review

Seismic waves travel all around the world.

Seismic waves can be detected with a sensitive instrument called a seismograph. A seismograph consists of a weight attached to a spring or a wire.

A pen is attached to the weight and records any movement of the Earth on a sheet of paper that is wound around a constantly rotating drum.

When the Earth is still, the pen records a straight line but when the Earth moves, the pen records a wavy line.

The higher the wavy lines the stronger the earthquake.

From data recorded by a seismograph, seismologists are able to determine the exact arrival times of both P waves and S waves.

Then seismologists calculate the time difference.

By using the time differential, seismologists can calculate the distance their recording station is from an earthquake.

This does not tell each seismologist the direction of the earthquake.

Using a compass, each seismologist draws on a map a circle around his recording station using the calculated distances the radius of the circle.

The location of the earthquake’s epicenter is the point all three circles intersect each other.

Lab: Earthquake Epicenter

Seismologists use the height of the tallest wavy lines to calculate the strength of the earthquake.

The scale used to measure the strength of an earthquake is the Richter Scale.

The scale was developed by the California seismologist Charles Richter back in 1935.

The Richter magnitude is related to the maximum amplitude of the S wave measured from the seismogram.

Any number above 6 indicates a very destructive earthquake.

Because there is a great range in the sizes of different earthquakes, the Richter scale uses logarithms.

A magnitude 7 (M 7) earthquake is 10 times as large as a magnitude 6 earthquake, and releases over 30 times more energy.

Earthquake Fun Facts What was largest recorded earthquake in the United States? A magnitude 9.2 that struck Prince William Sound, Alaska on March 28, 1964.

What was largest recorded earthquake in the world? A magnitude 9.5 in Chile on May 22, 1960.

Alaska What is the most earthquake-prone state?

Alaska experiences a magnitude 7 earthquake almost every year, and a magnitude 8 or greater earthquake on average every 14 years.

Florida & North Dakota What is the least earthquake-prone states?

What was the world’s deadliest recorded earthquake ? In 1556 in central China. It struck a region where most people lived in caves carved from soft rock. More than 830,000 people were killed.

In 1976, another deadly earthquake struck in Tangshan, China, where more than 250,000 people were killed.

Earthquake damage can range from minor

to major!

To measure the intensity of an earthquake, scientists have developed the Modified Mercalli Scale.

A number is given to each recording location based upon the Modified Mercalli Scale and placed on a map.

Points of equal scale on the finished map are connected to determine each different circle of intensity.

Lab: Earthquake Epicenter

Research Project: Virtual Earthquake

Earthquakes The Inside Story!

Mechanical Engineering

Elasticity

Elasticity is not Flexibility

Elasticity An object’s ability to return to its original shape after being stressed.

Stress Force/Area

Types of Stress

Tension & Compression Stress

Shear Stress

Compression Stress vs. Shear Stress

Hydrostatic Stress

When you apply a stress to an object, you causes a change in the object’s shape.

Deformation Change in shape of an object.

Strain The amount of deformation.

Strain

Elasticity Testing Device

Stress-Strain Curve

Elastic Limit

Which Material A or B?

Which Angle?

Which Construction Material?

Which Steel?

Lab: Material Stress

Where 2 plates come together is called a Fault.

An active fault normally causes a crack in the Earth's crust.

Lab: Fault Motion

The are 3 Main Types of Faults

Normal Fault Rocks are pulled apart. Result of tensile forces. One side of the fault is moved down relative to the other side of the fault.

Reverse Fault Rocks are pushed together. Result of compression forces. One side of the fault is pushed up relative to the other side of the fault.

Slip Strike Fault Movement of both sides of the fault is horizontal. Result of shear forces. One side of the fault slides past the other side of the fault.

Earthquake Prevention

Earthquake Prediction

Earthquake Belts

Earthquake Prediction

Earthquake Damage Prevention

Blocks cut with an internal angle, so as to 'fold' the stone around corners.

The use of metal ties are early examples of earthquake 'preventative'.