seismograph

Introduction

You're sitting in your easy chair, watching a favorite television program. As you reach for your tall glass oflemonade there is a sudden and unexpected noise. You hear a short rumbling sound and you feel a sharpjolt. You drop your television remote and notice the pictures on the wall are tilted and some of the thingson shelves have fallen down. You begin to speculate on whether it was thunder or an explosion, or perhapsmaybe a sonic boom. A shelf with plates ;crashes to the ground and books and pictures jostle and shuffleabout on the shelves before they crash to the floor and join other fallen objects. Finally you feel the shakingstop, but you notice that the lemonade in your glass is still slightly vibrating. Your heart pounds as you realizethat you have just experienced an earthquake.

Earthquakes can be scary events; therefore, it is fortunate that there are rarely strong ones in earthquakeprone areas of the world. Many buildings and homes are built to withstand the violent shaking and tremorsthat accompany strong earthquakes. Due to the unpredictable and destructive nature of earthquakes, theyare one of Earth's most potentially dangerous and disastrous natural phenomenon. The unpredictabilityof earthquakes is due to the difficulty in finding clues that could determine them. Most of the signs fordetermining earthquakes are inaccessible and hidden miles below the Earth's surface.

When earthquakes do occur, the sudden release of seismic wave energy is recorded using an instrument knowas a seismograph (from the Greek seismos - a tremor, and graphs - to write). A seismograph instrumentrecords the seismic waves of an earthquake similar to the way you use your ear to detect the sounds ofsomeone tapping against a wall. When you tap on a wall, you try to detect for changes in the density of thematerials behind it. You can't see the structure of the wall but different sounds of the tapping can be relatedto the materials within it. Similar to the tapping on the wall, earthquake waves can be studied from the surfaceand the types and densities of materials that they pass through can be determined. It is the intention of thiskit to provide the student with an understanding of how earthquakes occur and the importance of usingseismographs to study them.

Materials List and Assembly:

1. Base2. Paper Roll3. Dowel4. Support Bar5. Wire Arm6. Eyebolt7. Nut8. Medium Washer9. Medium Washer10. Wing Nut11. Rubber Grommet12. Stylus13. Rubber Band14. Nut15. Small Washer16. Lg. Washer17. Screw

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Earthquakes and Seismic Activity

In order to study seismic activity we must understand how it originates from earthquakes. Fractures in theLithosphere (crust) of the earth are continually made due to the drift of continental plates on the mantle ofthe Earth and flow of magna from its deep infrastructure. An earthquake occurs as continental plates andfractures grind and scrape against each other. These fractures are called faults and can vary in size from a fewcentimeters to thousands of kilometers. When an earthquake occurs on a fault, the rock and sediment on oneside of the fault slides horizontally or at an angle to the rock and sediment on the other side. The sudden slipof built up stresses along a fault releases energy as sound and shock waves that travel through lower rock.Many of these waves are absorbed and die out before we even notice them, but larger building up of stressesor potential energy creates greater waves that die out less slowly. The movements ofthe waves created helpus to detect and study tremors andseismic activity.

Ocean ridge(spreading)

Heated transform faull

Cool Lithosphere

Hot asthenosphere

X Shallow earthquakes(Tension on ridges: Internal slip on transform faults)

• Deep earthquakes(Mainly showing thrusting and down-dip compression)

Rising magma

A good example related to earthquakes would be the formations of ice on top of a body of water. Imaginethe surface of the body of water having multiple individual pieces of ice that meet each other. If an air bubble,representing magma from the inner core of the planet releases upward and exerts a stress on one of the piecesof ice, the stress may eventually cause a slip or motion in the ice. This creates a wave in the water underneaththe ice and through the rest of the ice. This energy will eventually die out as it travels further from the sourceand as it is absorbed and changed to other forms of energy such as heat and sound.

Do earthquakes occur where you live? Perhaps they do and you may have already experienced a strongearthquake at your home or school. Such places are called seismically active areas. Use the following mapto determine if the area where you live is seismically active.

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