Hypothesis | We predict that there will be more snow in Evanston than in California, Kentucky, southern Illinois, and Alabama. We think Pennsylvania will have the most snow and California the least. We predict that there will be the most rain in California and that Alabama will also have a lot of rain. We think Alabama will have the least amount of snow. We predict that Kentucky will have a lot of rain but little snow. We think there will be different amounts of rain in different places in Evanston and Skokie. |
| We predicted that there would be different amounts of precipitation around the United States during a given month. Further, we felt that there would even be different amounts of precipitation in the different areas of Evanston and Skokie that we live in. We collected data of precipitation in different parts of the country via e mail. Each week, each classroom sent us the amount and the type of precipitation that fell during the previous week. Additionally, we collected rain data at our own homes each week with precipitation gauges we had made. We used the medians of our individual weekly data for our data included in this experiment report. There were different amounts of precipitation across the country as well as in our own area. Because of El Nino, we had no snow during the entire month of February while California had a great deal. If we performed this experiment again, we would try to be more accurate in our collection of our own data. We would also try to get more participants. | |
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Construct rain gauges for each student in Room 204 to take home and install in a safe, open place. Measure the amount of rainfall and/or snow each week and record the data.Check e mail for data received from each of the participating schools. A standard rain gauge is an instrument that measures the amount of rain that falls in a certain place over a period of time. The National Weather Service uses a rain gauge that is shaped like a cylinder and has a removable cover. Inside the cylinder, is a long, narrow tube where the rain falls and is subsequently measured. The top of the tube is connected with a funnel. The rain falls into the funnel and then into the tube. The mouth of the funnel has an area ten times as large as the tube. Therefore, if an inch of rain falls into the funnel, it would fill ten inches of the tube. The rainfall is measured with a ruler. After it is measured, its tube is emptied out and the results are recorded. The rain gauge that we used at school is shaped like a rectangular prism on three sides and the fourth side is on an angle. We used the metric system for measurements.  The rain gauges we made for our homes and that classes around the country that collected data for us used were made out of 2 liter plastic soda pop bottles. We dug them into the ground near our homes and emptied them each week after we measured the rainfall. There was no measurable snow during the entire month of February in the area of our school. (Alex)  El Nino is Spanish for “Christ Child”. Fishermen in Peru and Ecuador began using this term to refer to the coastal warming that began around the Christmas season and lasted for several months. It has developed into a term meaning an “abnormal warming event.” The winter of 1982-83 was the strongest El Nino this century and not only affected the South American coast, but the entire world also. This year, El Nino has shown its effect on Evanston. (Russell, Joe) Sacramento, California--a warm area which is the capital of California. The Sacramento River runs through the town into the Pacific Ocean. They had so much rain in February that they had to close the schools. (Eugene, Eliza, and Megan) Spanish Fort, Alabama--located about ten minutes from Mobile and three hours from New Orleans. Generally, they have many hurricanes and tornadoes in March and April. They also have many tornadoes in the late summer. They are the wettest city in the United States. (Danny, Amy) Ulster, Pennsylvania----located in northeast Pennsylvania, twelve miles from the New York border. It is a rural area with many farms. Their rain gauge got buried when they had 45 cm of snow. (Russell, Alex) Cynthiana, Kentucky--a rural town located in the bluegrass area of Kentucky. They have beef cattle, sheep, chicken, and tobacco farming. There is also coal in the area. During February, they had 120 cm of rain. They generally get snow here, but not as much as they got all at once (53.5 cm). (Kasha, Ryan) Peoria, Illinois--a city in central Illinois. It is near the Senachwine Lake. Peoria is an important farming area in the center of Illinois. The area is called the Till Plains. It was odd that it snowed very little during February, and one of the weeks had no precipitation at all. (Cara, Joe) Evanston, Illinois--large city next to Chicago. It is a completely urban area. It was odd that there was only rain in February, and very little at that. Generally, we expect snow at this time of year. | |
 Median Amounts of Rain Data Collected at Our Homes in Evanston/Skokie, IL
We discovered that our hypothesis about snow and rain were wrong as to where the most snow and/or rain would fall. However, our hypothesis about there being different amounts in our neighborhoods and across the country were accurate. Evanston had the least amount of precipitation of all the cities and Cynthiana, Kentucky had the most. California did not have the most amount of rain, and Spanish Fort, Alabama did not have the least. There were different amounts of precipitation in different parts of Skokie and Evanston. There were very different amounts of precipitation in different parts of the country and even from week to week. The amounts of rain varied from a low of 1.9 cm in Spanish Fort, Alabama to a high of 69 cm in Cynthiana, Kentucky. There was no snow in Sacramento, California, Spanish Fort, Alabama, nor in Evanston, Illinois. However, Cynthiana, Kentucky recorded 53.5 cm of snow during the same month, and we had predicted that Evanston would have more snow than they would. | |
| El Nino made the weather during the month of February very strange. In Evanston, we had no snow, which was very unusual for the month of February. However, there was a huge amount of snow in California, and floods occurred in both Kentucky and California. | |
DeMers, Elaine, Fourth Grade Teacher, Taylor Street School, Sacramento, CA Heald, Blair, Teacher of Gifted Classes K-7, Spanish Fort School, Spanish Fort, AL Hughes, Kathy, Kindergarten Teacher, Sheshequin-Ulster Elementary School, McDaniel, DeAnna, Fourth Grade Teacher, Southside Elementary School, Titus, Nancy, Second Grade Teacher, Hollis Grade School, Peoria, IL Web Site: http://www.eduzone.com/tips/science/showtip3.htm Web Site: http://www.pbs.org/wgbn/novulehim/resources/glossary.html Web Site: http://www.pmel.noaa.gov/toga-tao/el-nino-report.html#part 2 World Book Encyclopedia, Vol. 16, pp. 126-127, 1996. |
samedi 21 février 2009
Does the level of precipitation differ in various parts of the United States?
Does the amount of moisture in the atmosphere vary from place to place?
Measuring Cloud Cover
During the day the sun is always shining, so the amount of sunshine reaching the ground depends on the amount and duration of any cloud cover. The amount of cloud cover is usually given in units called oktas.
Each okta represents one eighth of the sky covered by cloud. Clear sky /1 okta / 2 oktas / 3 oktas / 4 oktas / 5 oktas / 6 oktas / 7 oktas / Overcast
Using a Cloud Mirror
You can use a cloud mirror to simply measure oktas. Divide a large mirror into a grid with 16 equal squares using a dark crayon. Lay the mirror on the ground somewhere you can see the whole sky.
Count the number of grid squares, or fractions of squares with cloud in them. Divide that number by two to convert sixteenths into oktas.
http://www.bbc.co.uk/weather/weatherwise/activities/weatherstation/cloud_measuring.shtml
Measuring Humidity
There is water vapour in the air at all times. Humidity is the amount of water vapour present in the air and we can measure this using a hygrometer.
Relative humidity is the ratio of the actual amount of moisture in the atmosphere to the amount of moisture the atmosphere can hold. Therefore, a relative humidity of 100% means the air can hold no more water (rain or dew is likely), and a relative humidity of 0% indicates there is no moisture in the atmosphere. Relative humidity is used by meteorologists to help predict the weather, by pathologists to predict disease development on plants, and by agricultural scientists to estimate evapotranspiration
Relative humidity, combined with air temperature, can be used to estimate the actual amount of moisture in the atmosphere, sometimes referred to as precipitable water. Water vapour acts as a green house gas by trapping infrared radiation reflected from the earth. This explains why desert temperatures can become much lower at night, as there is little moisture in the air to trap the heat.
Hygrometer
The best hygrometer is one which has two thermometers - one of which has its bulb wetted continuously by a wet cloth. This is called a Mason's or a 'wet-and dry-bulb' hygrometer. Air passing over this wet bulb evaporates some water and lowers the wet bulb temperature by an amount that depends on the humidity of the air. To demonstrate this cooling, wet your finger and blow in it. The humidity can be found by noting the difference in temperature between the wet and dry bulb and looking up the RH value in a set of tables. (see attached). The relative humidity (RH value) is the amount as a percentage of that required to saturate the air completely.
http://www.uswcl.ars.ag.gov/exper/relhum.htm
Measuring Pressure
Barometers are used for measuring pressure. You can make a simple barometer but a proper one is needed to make correct observations.
The simplest and cheapest is a basic aneroid barometer which has a partial vacuum in a special metal box. This expands and contracts as air pressure changes, moving a pointer around a dial. Measurements are given in millibars (mb) or in hectopascals (hPa), identical in value. You must adjust your barometer to sea-level and it is best to put it inside a screen.
Measuring Rainfall
Rain gauges are required to measure rainfall and should be located in an open area, away from anything that might cause a shadow effect. It is possible to make a simple gauge out of a 2 litre plastics drinks bottle. The instructions are given very clearly at the website
http://weblife.bangor.ac.uk/cyfrif/eng/activities/spring/rain/pupilnotes.htm
Temperature: max and min
Special Max/Min Thermometers
A special maximum and minimum thermometer actually records the highest and lowest temperatures during a particular time period, usually one day. There are two types - the liquid in glass type (known as 'Six's thermometer') has little tiny metal markers inside the tube which are pushed around by the liquid and read against a scale. The bimetallic dial type has pointers which are very easy to read. Both need to be reset after every reading.
Describe how fog forms
"Fog in a Bottle"
Fog is a cloud that forms just above the ground. It's spooky and neat. Really thick fog can reduce you to seeing only a few feet in front of you. It can be a real hazard to cars, planes and boats.
There are two kinds of fog, advection fog and radiation, or ground fog.
Advection fog is common along the pacific coast of the United States. Warm, moist air over the Pacific Ocean are blown inward. When that air moves over colder coastal waters, it cools quickly and fog forms. The fog is moved inland by the same westerly winds.
Advection fog plays an important role in the life of California Redwood trees. The Redwood trees have very shallow roots. They depend on water from sources other than water deep underground. What the trees do not get from rain, they get from the fog. Advection fog deposits moisture on the pine needles which then drips to the ground and is absorbed by the roots.
The other kind of fog is radiation, or ground fog. This fog is common lots of places. It forms when a layer of warm, moist air forms low to the ground. A layer of cooler, dry air forms overtop. As the ground cools, the warm, moist air is cooled quickly. As the air temperature lowers, small droplets of water condense, which we see as fog.
Radiation fog forms most often on cool, clear nights with a very slight breeze. It forms first in low valleys and spreads outward so long as conditions remain the same.
Make Your own Fog in a Bottle!
It's easy to simulate the formation of radiation fog. All you need are two bottles with a narrow enough neck that you can stick an ice cube into the mouth. Fill one bottle about half way with very hot water (it doesn't need to be boiling.) Fill the other bottle with about 1 inch of cold water.
After several minutes, pour out all the hot water but 1 inch. Now place an ice cube in the mouth of each bottle. Observe what happens in both bottles.
What's in the soil?
| | (256) 430-0001 Mr. Johnston (teacher) & Mrs. Carter (student teacher) carter831@hotmail.com Primary Authors: Natasha, Danny, Adam, Josh "WHAT LIES BENEATH"Introduction
Materials and Methods
Results
Discussion
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What is a sink hole? Explain how it is formed and where it is more likely to be found
Sinkholes
The most damage from sinkholes tends to occur in Florida, Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania. The picture to the left shows a sinkhole that quickly opened up in Florida, apparently eating a swimming pool, some roadway, and buildings.
Areas prone to collapse sinkholes
The map below shows areas of the United States where certain rock types that are susceptible to dissolution in water occur. In these areas the formation of underground cavities can form and catastrophic sinkholes can happen. These rock types are evaporites (salt, gypsum, and anhydrite) and carbonates (limestone and dolomite). Evaporite rocks underlie about 35 to 40 percent of the United States, though in many areas they are buried at great depths.
Sinkholes can be human-induced
The overburden sediments that cover buried cavities in the aquifer systems are delicately balanced by ground-water fluid pressure. The water below ground is actually helping to keep the surface soil in place. Ground-water pumping for urban water supply and for irrigation can produce new sinkholes In sinkhole-prone areas. If pumping results in a lowering of ground-water levels, then underground structural failure, and thus, sinkholes, can occur.
What is "weathering"? Demonstrate how it happens to mountains
Our Weathering/Erosion Experiment
(From our mini-unit on weathering and erosion.)
We conducted this experiment in our backyard:
Michael mounded dirt in an area of the garden. He insisted on putting a chunk of dirt on the top of his "mountain". I felt it would fall off... hmmmm, another experiment!
Once the mountain was made, we now had to exercise patience to watch it erode. We also had to keep the neighbor kids off of it!
Each week we would go out and measure that mountain. It started as 42" wide, 19 1/2" tall, including the chunk. We had a chart we filled out. On this, we would log the date, height, width, observations, and make a little drawing of the mountain on our chart in a 1" x 2" square.
After just two weeks, the dirt mound had spread out more than 2 inches and had worn down about 3 inches.
After a few weeks (and several rainstorms), the mountain showed clear signs of weathering:
We would have continued with the measurements for the twelve weeks the experiment suggested, but something or someone got into the dirt mound during the night and we could no longer take accurate measurements. But we did get to see the effects of the weather on that dirt mound!
By the way, Michael thought it was important to wear the same clothes for each photo. :-)
More on weathering and erosion. We conducted many of these experiments, too!
Weathering - When rocks are worn down by water, wind, or other means, that is weathering. Soil is made up of weathered rock particles, so without weathering, there would be no soil. Try the following activities to see how rocks can weather.
How Do Chemicals Weather Rocks?
Place an equal number of limestone or marble chips in each of two jars. Cover the stones in one jar with water and those in the other with vinegar; then screw lids on the jars. Allow the jars to stand overnight. You may notice some bubbles forming in the jar with the vinegar. Ask the students to speculate about what this might mean. The next day, pour out the liquid from each jar into separate bowls. Label the bowls "water" and "vinegar". Allow the water in the bowls to evaporate. Compare the amount of solid material remaining in the two bowls. The bowl that contained vinegar will have a larger amount of solid material. (Limestone, marble, and other carbonate rocks react with acid to form carbon dioxide and soluble salts. Rainwater is often acid and can erode limestone easily. Acid groundwater dissolves limestone underground, forming caves and sinkholes. Study or visit any caves or sinkholes in your area. Examine other types of rock to see if they react to vinegar in the same way as carbonate rocks.
How Do Streams Weather Rocks?
Place some small, freshly broken pieces of rock or brick in a large plastic jar. Softer rocks such as sandstone, shale, or limestone work best. Fill the jar about halfway with clear water. Put aside some other pieces of the broken rock. Close the lid of the jar and shake it 1,000 times. Remove the rocks and note any changes in their appearance compared with the rocks that were not shaken. Describe these changes. Filter the water through a piece of filter paper or funnel lined with paper towels. What do you see in the filter paper? You may want to experiment with different types of rock to see what types will change more. What might happen to rocks in a stream? (Rocks in streams are weathered by water and movement.)
How Does Ice Weather Rocks? (Teacher Demonstration)
Completely fill a glass jar with water and cap it tightly. Place the jar in a resealable plastic bag. Put the jar and the bag in a freezer overnight. When you remove the jar, it will be broken. Handle and dispose of the broken glass carefully. Ask students to predict what this demonstration might tell us about rocks and weather. (When water freezes, it expands. When it freezes in cracks in rocks, the expansion can cause the rock to break.)
Erosion - When particles weathered from rocks are carried away, it is called erosion. Erosion is responsible for wearing down exposed places and depositing sediment in level places.
What Happens To A Mountain?
Build a "mountain" of soil 50 cm high in an undisturbed location in your schoolyard. Observe the mountain once a week for three months. Have students measure its height and width and note any changes in its surface. After observing the mountain for an extended period of time, ask students to suggest what forces might have caused changes in your mountain. How long do they think the mountain would remain if you left it there? (Our experiment above.)
How Does Vegetation Affect Erosion?
Punch holes in the bottom of a plastic cup to make a sprinkler. Place three to five centimeters of soil in each of two planting flats. Sprinkle grass seed on the soil in one of them and cover lightly with soil. Water both flats every day with the sprinkler until the grass is five centimeters tall. Prop the ends of both flats up at a moderate angle with bricks or blocks. Sprinkle each flat with water equally until you observe soil erosion. In which tray did the soil erode more? What might be the effect of removing plants like trees from a steep mountainside? How could soil erosion be controlled in steep places? What other factors can students think of that would affect the amount of erosion? Have students identify any areas in your community that are steep. Take a field trip to look for signs of erosion.
Wave Action - How Beaches Are Formed
Slope a generous amount of sand against one end of a dishpan. Add water until the sand is about half covered. Use the side of a ruler to generate steady, even waves in the tray. Have students observe the action of the waves on the sand. They should see that the water removes sand from the upper part of the "beach" and deposits it below the waterline. This is how sandbars and barrier islands are formed. If you can make very small, rapid waves, you may see that the sand is redeposited on the beach.
How Does Water Carry Particles Of Rock And Soil?
Mix some gravel, sand, mud, silt, and clay in a large jar. Add water to the jar. Cover the jar with the lid; then shake the jar vigorously. Have students observe the jar over a period of time and note how long it takes for the different materials to settle on the bottom. Do they see different layers on the bottom? What is different about them? Have students think about different kinds of streams and rivers. Where would they expect to find a rocky or gravel bottom? Where would there be a muddy or silty bottom? Which type of material might be carried for the longest distance? (The smaller particles remain in suspension in the water for the longest time. They have a larger ratio of surface area to mass and therefore experience more resistance from the water as they sink.)
Model of the Grand Canyon
Cut out the middle section of one of the short sides of a cardboard box. (The lid of a paper box works well.) Cover the bottom of the box with a layer of mud or wet soil. Allow the mud to dry. Cover this layer with another layer of a different color. Repeat with many layers until the box is full, allowing each layer time to dry. Then tilt the box under an outdoor faucet with the open end downward, and run water in a steady stream onto the top end. Have students observe how a canyon is formed. Ask students to describe the effect the different layers have on the erosion of the canyon.
Book List:
Geography From A to Z: A Picture Glossary by Jack Knowlton
The Beginning Of The Earth by Franklyn M. Branley
The Magic School Bus Inside The Earth by Joanna Cole
Surtsey: The Newest Place On Earth by Kathryn Lasky
The Rock by Peter Parnall
(All information for this mini-unit came from a Mailbox Magazine - issue date is unknown.)
Build a model to demonstrate how earthquakes are caused
Summary
The apparatus consists of a heavy object that is dragged steadily with an elastic cord. Although pulled with a constant velocity, the heavy object repeatedly slides and then stops. A small vibration sensor, attached to a computer display, graphically monitors this intermittent motion.
This intermittent sliding motion mimics the intermittent fault slippage that characterizes the earthquake fault zones. In tectonically active regions, the Earth's outer brittle shell, which is about 50 km thick, is slowly deformed elastically along active faults. As the deformation increases, stress also increases, until fault slippage releases the stored elastic energy. This process is called elastic rebound.
Detailed instructions are given for assembly and construction of this demonstration. Included are suggested sources for the vibration sensor (geophone) and the computer interface. Exclusive of the personal computer, the total cost is between $125 and $150.
Construction of Earthquake Machine
Read through this and the Setup and Operation sections before purchasing any equipment, as some trouble-shooting alternatives are offered.
Materials for rock-slide:
Base for rock-slide: 3' 5" of 1"x6" pine
Sides for rock-slide: 3' of 1"x2" pine
Stop for rock slide: 7" of 1"x2" pine
Elastic shock cord: 15" long by 1/4" diameter
Rock with a flat side, or a brick
Rough sand paper to cover base of rock or brick: may be required to get best sliding properties.
Non-elastic cord: 10'
Three C-clamps: One to clamp the winch to one table and two to clamp the rock-slide to another table.
Screws: 10 with a length of 1 1/4"
Materials for winch:
1 13" length of 3/4" PVC pipe, cut into 3 pieces with lengths of 7", 3", and 3"
2 90 degree PVC junctions
1 straight PVC junction
PVC cement
1 2"x4" (wood) 1' in length
2 pieces of 1"x6" wood cut 8" long
4 2 1/2 " long wood screws
Materials for seismic display:
Geophone: A small 8 to 14 Hz vertical exploration geophone may be purchased from some surplus stores. For example: All Electronics Corporation, (800) 826-5432, http://www.allcomp.com/, currently (November 1998) sells their catalog number GP-1 geophone for $8. Also Arlen Juels of Seistex '86 Inc. has a number of used exploration geophones that he is willing to provide to teachers for the cost of shipping. He can be contacted at AJuels@seistex.com.
Analog to digital converter (AD) and display software: The least expensive AD unit that I have been able to find is Dataq's DI-150-SP, which sells for $100. This unit attaches to a PC serial port and includes software for MS Windows that will display the seismic data in real time. Dataq Instruments (888) 666-2907; http://www.dataq.com.
Assembly
Using 1 1/4" screws, attach the sides and stop to the rock-slide base, as indicated in the diagram below.
Drill a 1" diameter hole in each of the 1"x6" boards. The center of the holes should be 1 3/4" from the 6" edge of the wood, as indicated in the sketch below. Using the four 2 1/2" wood screws, attach the sides of the winch to the 2"x4" base. The extra length on the base is to allow more room for clamping the winch to a table. Using PVC cement, attach the three pieces of PVC together using the two 90-degree junctions, as indicated. Then slide the 7"-long pipe through the two holes in the winch. If the pipe does not slide easily in the holes, use a round file to enlarge the holes. Glue a straight PVC junction to the end of the 7"-long pipe to keep it from sliding out of the winch. Drill a 1/4" diameter hole through one side of the 7" section of PVC pipe. Feed one end of the non-elastic cord through this hole and tie a knot in the end so that the cord will be securely attached to the pipe.
Using the C-clamps, secure the winch to one table and the rock-slide to an adjacent table. The use of two tables prevents the winch from vibrating the table on which the geophone is located.
Securely attach a loop of non-elastic cord to the rock or brick, leaving an open loop on one dangling end of the cord. Wind the rest of the non-elastic cord onto the winch. Secure one end of the 15" piece of elastic shock cord to the winch cord and the other to the dangling end of the cord attached to the brick or rock.
Setup and Operation
Set up the geophone and display computer on the table with the rock-slide. The geophone does not have to be on or right next to the rock-slide. In fact, it is better to have it a few feet away so that it is clear that the vibrations from the sliding rock must travel some distance along the tabletop to reach the sensor. Adjust the display software so that the trace is scrolling on the screen and a slight tap on the table is clearly registered.
The distance between the winch and the rock-slide should be adjusted so that the shock cord does not begin to wind onto to winch; this maintains a constant elastic component during the entire travel of the rock or brick. Next try pulling the rock or brick along with the winch. The speed should be such that it takes 30 seconds to a minute to move the entire length of the rock-slide. If it slides steadily rather than in discrete events (earthquakes), an adjustment is necessary. Try increasing the friction or using a longer or stretchier section of shock cord. Friction can be increased by gluing coarse sandpaper to the sliding surface of the rock or brick, by using a heavier rock, or by using two bricks, one on top of the other. If the rock slips too far in one event, such as more than half of the entire length of the rock-slide, then decrease the weight of the rock, decrease the length of the elastic cord, or use a less stretchy elastic cord.
When the adjustments are complete, the rock should generate approximately 4 to 10 events per run, and each of these "earthquakes" should be clearly registered on the computer screen display (the seismogram).
Earth Science
Most of the Earth's processes are slow, but steady. This makes them difficult to comprehend, because little seems to happen on a human time scale. Mountains are slowly uplifted and even more slowly eroded away; rivers slowly cut gorges and transport sediments to growing deltas, but the pace is so slow that even after many generations little seems to have changed. Earthquakes are an exception; they involve rapid enough slippage on a fault to cause waves of vibrations to be radiated outward. The vibrations can be felt and, if the fault intersects the surface of the earth, the resulting displacement can be observed directly.
Plate Tectonics. Plate tectonics is the study of the consequences of the slow motion between the plates that make up the outer shell of the earth. There are about a dozen major plates and they are about 50 km thick. The temperature and material properties at the base of the plates are such that they can slip steadily without producing any earthquakes. However, when a plate itself is deformed, due to mountain building, for example, or when one plate must slide past another, earthquakes are produced. For years, and in some cases as much as many hundreds of years, very little slip may occur across a portion of one of the boundaries between two plates that are in relative motion with respect to each other. During this time both plates are deformed and bent elastically near the boundary, and all the while the stress in the region is increasing. Eventually, during an earthquake, the plates quickly slide past one another and the stress is greatly reduced. This process of slow deformation followed by rapid release is called elastic rebound and was first proposed by H. F. Reed following studies of the 1906 San Francisco earthquake.
The following figure by USGS seismologist Will Prescott schematically illustrates a fence crossing the San Andreas fault in California. The figure is from the web page http://quake.wr.usgs.gov/more/1906/reid.html.
An excellent tutorial on earthquakes, which was developed by the Southern California Earthquake Center, is available at http://www.scecdc.scec.org/Module/ . Although aimed at high school and undergraduate levels, this module would also be a good source of information for middle school students who wanted to learn more about this subject. Especially helpful are the animations of the various types of faulting.
Hazards. The vibrations from large earthquakes can be strong enough and last long enough to be a serious hazard. They can cause man-made structures such as buildings and bridges to collapse and they can cause ground failures such as landslides. If an earthquake produces rapid deformation of a body of water, be it uplift of the floor of the ocean or movement of a lake or fjord, a large and potentially deadly wave of water can be generated. When in the ocean, a wave of this sort is called a tsunami wave, whereas in a smaller body of water it is called a seiche. A small dish of water places on the table with the rock-slide will show small ripples following an "earthquake," analogous to the waves that could be generated in a lake.
Waves in the solid Earth. Some of the seismic waves generated by earthquakes are confined to the outermost layers of the earth (surface waves), somewhat like the ripples that travel outward on the surface of a pond from the point where a rock has hit the water. Other waves (body waves) travel outward in all directions, including straight down through the center of the earth. Much of what is known about the inside of the earth was learned from the study of the waves generated by earthquakes.
Compressional and Shear Waves. The three most common states of any material are solid, liquid, and gas. A material in any of these three states will resist having its volume changed by being squeezed or stretched. A compressional wave, such as a sound wave in air, consists of a series of compressions and stretches (called dilations) of the air as the sound travels outward from the source. Compressional waves can also travel in a liquid or a solid. In a compressional wave, the back and forth motion of the material is in the same direction as the wave is traveling.
The figure below shows a compressional wave traveling to the right. The material is alternatively compressed and expanded from its resting state as the wave passes through.
Of the three states, solids are the only one that will, upon being bent, return to their original shape. Another way to say this is that solids resist shearing. The diagram below illustrates the difference between shear and compression.
Unlike liquids or gasses, solids can transmit waves that involve back and forth motion of the material perpendicular to the direction that the wave is traveling. The figure below shows a shear wave traveling to the right. Note that the material is moving in and out of the page, perpendicular to the direction of wave travel.
A slinky may to used to demonstrate both compressional and shear waves, which can be seen traveling along the length of the slinky. Compressional waves are generated if one end of a stretched slinky is pushed quickly along the axis of the slinky and shear waves are generated if one end is displaced quickly in a direction perpendicular to the axis of the slinky.
Physics
Energy, friction and waves. It is interesting to consider the flow of energy that is involved in making the rock-slide. Chemical energy from one's muscles is first used to turn the winch handle. At first the rock does not move, so the energy is stored in the elastic cord. The more the elastic cord is stretched, the more energy is stored within it, and the greater the force on the rock. When the static friction that is holding the rock in place is exceeded, the rock will start sliding. Because sliding friction is less than static friction, the rock will continue sliding some distance until the force from the elastic cord is equal to the sliding friction that is resisting motion of the rock. The energy that was slowly stored up within the elastic cord is quickly released and converted into kinetic energy of the moving rock. As the rock slides along, its kinetic energy is dissipated by heating up the sliding surfaces and by radiating energy in the form of elastic waves. The seismograph detects these elastic waves as they pass by, and they are displayed on the seismogram.
Magnetism. The geophone works by magnetic induction, which is the term for the generation of a voltage within a conductor that is subjected to a varying magnetic field. A geophone consists of a coil of wire suspended by a spring. A strong magnet is attached to the geophone's case, so when the coil vibrates up and down on its spring it is moving with respect to the magnetic field of the magnet. This motion of the coil with respect to the magnetic field generates a voltage, and it is this voltage that is displayed on the seismogram.
A very simple geophone can easily be made by winding magnet wire on a small plastic cylinder, which is then mounted vertically. An old marking pen can be cut up to make the plastic tube. One end of a 4-inch-long piece of rubber from a rubber band is attached to a magnet that is just small enough to slide freely within the plastic cylinder. The other end of the rubber band is attached to a mounting point directly above the cylinder.
Any vibration will cause the magnet to bounce up and down within the coil and will produce a small voltage in coil wire. To see how the homemade geophone is working, it can be attached to the AD and computer display in place of the commercial geophone. Although not as sensitive, this illustrates the principal of how a geophone works. It is best to use a strong magnet, such as a rare-earth magnet, so that even a slight motion of the magnet will generate a detectable voltage. Sources of strong magnets include Radio Shack and All Electronics Corporation, (800) 826-5432, http://www.allcomp.com/.
Math
Graphing. The seismogram that is displayed on the PC's screen is a graph of the voltage produced by the geophone as a function of time. The voltage is proportional to the velocity of the coil with respect to the magnet, and for frequencies higher than the natural frequency of the geophone this voltage will be proportional to the vertical velocity of the table at the location of the geophone. Another time graph that the students may be more familiar with is the stock market average selling price versus time.
Logarithms. In seismology, the energy of the vibrations produced by an earthquake can vary enormously. The total energy of the seismic waves generated by the smallest earthquake that could be located by a local network of seismometers is about 2,000 joules (J). The largest earthquake ever recorded released 11,200,000,000,000,000,000 J of energy as seismic waves and was observed on seismometers all around the World. As you can imagine, it is not very convenient dealing with numbers that have such a large range. On the Richter magnitude scale, the magnitude of a 2,000 J event is minus 1.0 while the magnitude of the largest recorded earthquake was 9.5. The relationship between earthquake energy and magnitude is said to be logarithmic because the equation relating energy and magnitude includes a logarithmic term.
For energy, E, in joules, the equation is: log E = 1.5 M + 4.8 (this is log to the base 10).
Or expressed another way: E = 10 raised to the power (1.5 M + 4.8)
Or: Magnitude, M = (log E - 4.8)/1.5
Note that this indicates that an increase of one unit of magnitude results in 32 times greater energy release.
| Earthquake Energy as a Function of Magnitude | |||
| Magnitude | Energy Equivalent Weight of TNT* | Energy in joules (1 J = 1 newton meter) | Notes |
| -3.0 | 0.001 ounces | 2 J | 1.5 foot pounds (18 inch pounds) |
| -2.0 | 0.032 ounces | 63.1 J | 47 foot pounds |
| -1.0 | 1.0 ounces | 2E+03 J | 1,500 foot pounds |
| 0.0 | 32 ounces | 63.1E+03 J | |
| 1.0 | 63 pounds | 2E+06 J | |
| 2.0 | 1 ton | 63.1E+06 J | Only felt nearby. |
| 3.0 | 32 tons | 2E+9 J | |
| 4.0 | 1 kton | 63.1E+9 J | Often felt up to 10's of miles away. |
| 5.0 | 32 ktons | 2E+12 J | |
| 6.0 | 1,000 ktons | 63.1E+12 J | |
| 6.9 | 22,700 ktons | 1.41E+15 J | 1995 Kobe, Japan, Earthquake |
| 7.0 | 32,000 ktons | 2E+15 J | |
| 8.0 | 1 Mtons | 63.1E+15 J | |
| 9.0 | 32,000 Mtons | 2E+18 J | |
| 9.2 | 64,000 Mtons | 3.98E+18 J | 1964 Alaska Earthquake - Second largest instrumentally recorded earthquake |
| 9.5 | 180,000 Mtons | 11.2E+18 J | 1960 Chile - Largest instrumentally recorded earthquake |
*This is the approximate amount of TNT that would be required to generate high-frequency seismic waves of similar amplitude to those from an earthquake of each magnitude. This is based on the observation that a 1-kton explosion is approximately equivalent to a magnitude 4 earthquake (Evernden and others, 1986).
Computing Magnitude. The magnitude of the small "earthquakes" generated by the sliding rock can be computed if we know the energy released during the event. The force times the distance gives the energy. If a small fish scale is linked into the cord, between the winch and the sliding rock, then the force on the rock can be measured. If the distance of that the rock slides is also measured, then the energy can be computed, and from the energy the magnitude can be determined. (For this exercise we will ignore the portion of the energy that goes into heating the rock and the board due to friction and assume that all of the energy goes into seismic waves.) The units of inches of distance and pounds of force are not usually used in scientific investigations today, as the International System (SI) is almost exclusively used. In the SI system the unit of distance is the meter (1 m = 39.37 inches) and the unit of force is the newton (1 N = 0.225 pounds of force). However, because fish scales are usually not calibrated in newtons, and using a mixed English and metric system such as centimeter pounds seems a bit awkward at best, inch pounds are used in following table and graph. For more information on the SI system of units, see Dr. Russ Rowlett's web site at the University of North Carolina, http://unc.edu/~rowlett/units/sipm.html
Table of magnitude versus energy for the range 1 to 100 inch pounds. | |||
| 1 -3.83 2 -3.63 3 -3.51 4 -3.43 5 -3.37 6 -3.31 7 -3.27 8 -3.23 9 -3.20 10 -3.16 11 -3.14 12 -3.11 13 -3.09 14 -3.07 15 -3.05 16 -3.03 17 -3.01 18 -2.99 19 -2.98 20 -2.96 21 -2.95 22 -2.94 23 -2.92 24 -2.91 25 -2.90 | 26 -2.89 | 51 -2.69 | 76 -2.58 |
Probability. Predicting when the rock will slide is similar to the problem of predicting when an earthquake will occur. A very long-term prediction would be, assuming that the winch is turned steadily, that earthquakes will eventually take the rock from one end of the board to the other. A similar prediction, often called a forecast if it is not related to a specific earthquake at a specific time, would be that earthquakes will continue to occur on the San Andreas fault as long the Pacific Plate continues to move northwestward with respect to the North American plate. In California, the San Andreas fault is the boundary between these plates. One can also say in a qualitative way that the longer it has been since an earthquake has occurred on an active fault, the higher the probability that it will occur within the next interval of time. This is clear in the table-top earthquake demonstration because one can see the elastic cord stretch and thus increase the force on the rock. In a similar way today, global positioning satellite (GPS) measurements are being made of the deformation of the ground surface in areas such as California. If these measurements are continued for decades they will allow scientists to gauge which areas have been strained the most, and are therefore the most likely to experience earthquakes.
Social Studies
Hazard Mitigation. Many areas of the United States have the potential of experiencing a damaging earthquake. It is interesting to discuss the way society deals with this and other hazards. Are these issues that should be left to each individual, or is there a role for common action through governmental regulations? How safe is your school? Your home? There is a lot of information available from the Federal Emergency Management Agency (FEMA), including this page especially for kids: http://www.fema.gov/kids/quake.htm
Geography
Global Distribution of Earthquakes. An interesting project involving both geography and seismology is to plot the earthquakes that are located around the world for a few months. This requires a large map of the world and internet access. Each school day print out the list of earthquakes from this USGS web site: http://wwwneic.cr.usgs.gov/neis/finger/quake
For each earthquake place a colored stick-on dot on the map at the location indicated. Use red for earthquakes less than 50 km deep, orange for earthquakes between 51 and 150 km deep and yellow for even deeper events. After a period of some months, the global pattern of earthquakes will be clearly indicated on the map. Keep a list of all of the countries effected, and for an added challenge try to find the word for earthquake in the language of each country.
The pattern of colors will reveal the zones where an oceanic plate has slid under an adjacent plate and extends deep into the Earth. Note that these zones also have active volcanoes. An excellent publication that describes the relationships between plate motions, volcanoes, and the structure of the Earth is on the web site: http://pubs.usgs.gov/publications/text/dynamic.html
Acknowledgements
I am grateful for very helpful reviews of this report by Ed Cranswick and Susan Rhea. In addition, I thank Ross Stein for demonstrating the basic idea of using an elastic cord and a rock as an analog for earthquake faulting.
References
Evernden, J.F., Archambeau, C.B., and Cranswick, E., 1986, An evaluation of seismic decoupling and underground nuclear test monitoring using high-frequency seismic data, Reviews of Geophysics, v. 24, no. 2, p. 143-215