# Unit 3: Earthquakes/Volcanoes Volcanoes, Earthquakes, Elastic Rebound Theory, Natural Disasters.

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Unit 3: Earthquakes/Volcanoes Volcanoes, Earthquakes, Elastic Rebound Theory, Natural Disasters

Earthquake Discovery Lab Earthquakes are natural vibrations of the ground. Most quakes are caused by movement of the plates along large fractures (faults) in the crust. In this activity, you will model how the movements along these fractures can cause earthquakes.

The Plate SlideSlide Obtain 2 blocks of wood, sandpaper, and thumbtacks. Using Cornell Note pattern, prepare to record descriptors (steps) and data. Slide the large surface of the wooden blocks against each other. Describe the movement. (Draw a line to separate data) Repeat for side A, B, and C.

Plate Slide Experiment Next take a piece of sandpaper and attach it to the block of wood, with the sandpaper side exposed, using the thumbtacks. Now slide the two blocks against each other and describe the action. (You should have 4 sets of observations) Conclusion: What conclusion can you draw from this activity?

Report Out Each table will report out on their findings. Each table will then answer the following questions: –How does stress effect the movement? –How does surface affect the resistance (friction)? –How does the friction change movement? –Discuss the role of friction and stress on the movement of land.

Faults Fractures in the earth occur when a force is applied to the underlying rock, which movement occurs. Stress is the force per unit area acting upon a material. There are 3 types of stress that acts upon the Earth’s rocks: –Compression: decreases material volume –Tension: pulls the material apart –Shear: Causes the material to slip or twist

Types of Faults Slip Faults –Horizontal tension Sideways movement Normal Fault –Tension (Apart) Down on advancing block Thrust/Reverse Fault –Compression Uplift of advancing block

Examples of Faults Reverse Fault –Note the compression –Note the uplift San Andreas Fault –Pulled apart –Sideways movement

Inside an Earthquake Video 1: Live Footage

Earthquakes Waves Most earthquakes are caused by movements along faults. Recall from the lab, that some slippage along the faults is relatively smooth. Other movements, like the sand paper-sand paper show how some surface lock or snag. The tension builds until they reach the elastic limit and then the tension is released causing movement.

Three Types of Seismic Waves The vibrations of the ground during an earthquake are called seismic waves. Primary Waves or p-waves squeeze and pull the rock in the same direction the wave is moving –Inside the earth Secondary waves or s-waves are caused by rock moving at right angles to the wave. –Inside the earth Surface waves move in two directions, up and down and sideways from the fault. –On the surface

Wave Origin The waves originate at the place on the fault where the slippage occurs. P and S waves originate here. Focus –In the earth where the –Slip occurs Epicenter –Point on surface –Directly above Focus

Ride the Wave Scientist use special tools to measure the seismic waves. These are called Seismometers. This device records the movement as a rotating drum records time. The resulting graph is called a seismograph.

Measuring and Locating Earthquakes The amount of energy released during an earthquake is called its magnitude. Many news agencies describe the magnitude of the quake on a numeric scale, called the Richter scale. Each number represents the energy of a wave. Each increasing number represents an increase on the order of 10. –So a quake of 2.0 is 10 times more powerful than a 1.0. – 3.0 is 100 times more powerful than a 1.0.

Earthquake Magnitude Scale MagnitudeEarthquake EffectsEstimated Number Each Year 2.5 or lessUsually not felt, but can be recorded by seismograph.900,000 2.5 to 5.4Often felt, but only causes minor damage.30,000 5.5 to 6.0Slight damage to buildings and other structures.500 6.1 to 6.9May cause a lot of damage in very populated areas.100 7.0 to 7.9Major earthquake. Serious damage.20 8.0 or greaterGreat earthquake. Can totally destroy communities near the epicenter.One every 5 to 10 years

Putting it in Perspective Watch the video on the perspective of magnitude. Comparison of recent earthquakes Question: What can be learned by understanding the Richter scale in perspective to the higher the number?

Examples of Damage Santa Rosa, Ca –1906 –7.9 Anchorage, Ak –1964 –8.6 Tokai, Japan –2010 –6.6

Locating an Earthquake Scientists use simple geometry to locate the “epicenter” of the quake Where the 3 circles intersect is the location Wave Time A = 2 min B = 4 min C = 6 min

Earthquakes and Society Most earthquakes occur because of prolonged shaking of the ground by surface waves; sometimes it lasts more than a minute. Some buildings cannot withstand this motion and collapse. Collapsing buildings are responsible for the majority of deaths associated with earthquakes.

Earthquake Hazards Structural failure resulting from the “pancaking” of tall buildings. They walls give way and the floors fall, stacking one- on-top-of-another. Issues revolve around: – the building foundation –The height of the building

Land and Soil Failure Earthquakes can cause: massive landslides –Guatamela Liquefaction of soil –Disney Sinkhole Ground uplift –Hondorus Road

Tsunami Tsunamis are giant walls of water caused by the sudden uplift of the crust or by massive landslides caused by earthquakes. Japan Nov 3, 2011 Christmas Tsunami, Thailand

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