1. What's Shakin'? What are earthquakes ? Why do they occur ? Why can't we predict them ? What are earthquakes ? Why do they occur ? Why can't we predict them ? Although we still can't predict when an earthquake will happen, we have learned much about earthquakes as well as the Earth itself from studying them. We have learned how to pinpoint the locations of earthquakes, how to accurately measure their sizes, and how to build flexible structures that can withstand the strong shaking produced by earthquakes. Although we still can't predict when an earthquake will happen, we have learned much about earthquakes as well as the Earth itself from studying them. We have learned how to pinpoint the locations of earthquakes, how to accurately measure their sizes, and how to build flexible structures that can withstand the strong shaking produced by earthquakes.

2. Just the Facts An earthquake is a sudden shaking of the ground. They generate seismic waves which can be recorded on a sensitive instrument called a seismograph. An earthquake is a sudden shaking of the ground. They generate seismic waves which can be recorded on a sensitive instrument called a seismograph. The record of ground shaking recorded by the seismograph is called a seismogram. The record of ground shaking recorded by the seismograph is called a seismogram.

3. A Drop of Water Consider what happens when a drop of rain hits a pond of water. The drop disturbs the flat surface of the water and creates waves that travel outward in all directions from the disturbance. These waves travel on the surface of the pond, along the interface between the water and the air. Consider what happens when a drop of rain hits a pond of water. The drop disturbs the flat surface of the water and creates waves that travel outward in all directions from the disturbance. These waves travel on the surface of the pond, along the interface between the water and the air. Earthquakes create seismic waves which shake the ground as they pass. They sometimes cause buildings to topple. Earthquakes create waves just like waves of water moving across the ocean and waves of air moving across a field of wheat. Earthquakes create seismic waves which shake the ground as they pass. They sometimes cause buildings to topple. Earthquakes create waves just like waves of water moving across the ocean and waves of air moving across a field of wheat.

4. Earthquakes generate seismic waves which can be detected with a sensitive instrument called a seismograph. Earthquakes generate seismic waves which can be detected with a sensitive instrument called a seismograph. Advances in seismograph technology have increased our understanding of both earthquakes and the Earth itself. Advances in seismograph technology have increased our understanding of both earthquakes and the Earth itself. Perhaps the earliest seismograph was invented in China A.D. 136 by a m an named Choko. Perhaps the earliest seismograph was invented in China A.D. 136 by a m an named Choko. What is a Seismograph?

5. A long, long time ago This early eastern seismoscope consisted of a copper vessel with eight dragon heads attached to it, positioned above eight frogs. Each dragon head held a ball in its mouth, which, when dropped due to the strong shaking of an earthquake, would fall into the open mouth of the frog directly below it. By noting which frogs contained balls after a strong earthquake, it was possible to determine how the Earth had moved. in response to the earthquake

6. Getting Electric Because a magnet moving inside a coil creates a current within the coil, the movement of the ground during an earthquake can be converted into an electrical signal. Because a magnet moving inside a coil creates a current within the coil, the movement of the ground during an earthquake can be converted into an electrical signal. This signal could then be used to modify the projection of light onto photographic paper, or to move a needle across paper and trace out the wiggles of the Earth's shaking. This signal could then be used to modify the projection of light onto photographic paper, or to move a needle across paper and trace out the wiggles of the Earth's shaking.

7. Modern Day Seismograph

8. Networking Information Beginning in the 1960s, significant strides were made in the study of earthquakes and the Earth's structure with the deployment of the World-Wide Seismographic Station Network (WWSSN). This network consists of over 120 seismographs in 60 countries. Beginning in the 1960s, significant strides were made in the study of earthquakes and the Earth's structure with the deployment of the World-Wide Seismographic Station Network (WWSSN). This network consists of over 120 seismographs in 60 countries. The seismographs were put in vaults or old mine shafts deep in the Earth in order to make sensitive recordings of seimic signals free from the "noise" created by cars and other environmental factors. The seismographs were put in vaults or old mine shafts deep in the Earth in order to make sensitive recordings of seimic signals free from the "noise" created by cars and other environmental factors. This "global observatory" illustrates the international nature of global seismology and the essential cooperation in data exchange needed to study earthquakes. This "global observatory" illustrates the international nature of global seismology and the essential cooperation in data exchange needed to study earthquakes.

9. The Slinky and The Rope Earthquakes generate several kinds of seismic waves including P, for "Primary" and S, for "Secondary" waves. Earthquakes generate several kinds of seismic waves including P, for "Primary" and S, for "Secondary" waves. The P waves move in a motion similar to the motion of a slinky The P waves move in a motion similar to the motion of a slinky

10. S Waves S Waves S waves move in a shear motion perpendicular to the direction the wave is traveling. S waves move in a shear motion perpendicular to the direction the wave is traveling.

11. The P waves travel fastest through the Earth so they arrive at a seismograph first, followed by the S waves and lastly by the surface waves. The P waves travel fastest through the Earth so they arrive at a seismograph first, followed by the S waves and lastly by the surface waves.

12. Locatin' the Shakin' Seismologists locate earthquakes by measuring the time between the P and S waves in a seismogram. Seismologists locate earthquakes by measuring the time between the P and S waves in a seismogram. After a seismogram "feels" an earthquake, scientists compare the time difference of these waves to figure out how far away the earthquake is. After a seismogram "feels" an earthquake, scientists compare the time difference of these waves to figure out how far away the earthquake is. It takes at least three seismograms to locate exactly where the earthquake is. It takes at least three seismograms to locate exactly where the earthquake is.

13. Under Stress Because faults have friction, they resist the forces trying to move the pieces apart. As the forces build, the fault remains locked and the blocks get deformed because of the increasing stress. Because faults have friction, they resist the forces trying to move the pieces apart. As the forces build, the fault remains locked and the blocks get deformed because of the increasing stress. Eventually the stresses get so high that the fault breaks. This releases the built up stress and allows the sides of the fault to slide past one another. This is what we call an earthquake. Eventually the stresses get so high that the fault breaks. This releases the built up stress and allows the sides of the fault to slide past one another. This is what we call an earthquake.

14. How to Release Stress You can simulate the earthquake this by placing your hands together with your thumbs up. By pushing your hands together you create pressure between your hands. You can simulate the earthquake this by placing your hands together with your thumbs up. By pushing your hands together you create pressure between your hands. As you try to slide your hands apart, you create friction which stops you from sliding your hands easily. Stress builds up in your hands and arm As you try to slide your hands apart, you create friction which stops you from sliding your hands easily. Stress builds up in your hands and arm

15. Pick a Fault, any Fault You can try and visualize by placing a deck of cards between your hands with your thumbs pointed up and sliding your left hand away from you and your right hand towards you. You can try and visualize by placing a deck of cards between your hands with your thumbs pointed up and sliding your left hand away from you and your right hand towards you. The cards near the center of the deck are not offset very much, but the cards near your hands are offset much farther. The cards near the center of the deck are not offset very much, but the cards near your hands are offset much farther. In this example, your left hand represents the Pacific plate and your right hand represents the North American plate. The middle of the deck is where the San Andreas fault would be, and the outer cards represent how the motion between the Pacific and North American plates is accommodated on faults parallel to the San Andreas. Some of these other faults are located as far away as Nevada! In this example, your left hand represents the Pacific plate and your right hand represents the North American plate. The middle of the deck is where the San Andreas fault would be, and the outer cards represent how the motion between the Pacific and North American plates is accommodated on faults parallel to the San Andreas. Some of these other faults are located as far away as Nevada!

16. Measuring A Quake There are many ways to measure the size of an earthquake. Some depend on the amount of damage caused by the earthquake while others depend on the amount of seismic energy emitted by the earthquake. There are two popular earthquake scales. There are many ways to measure the size of an earthquake. Some depend on the amount of damage caused by the earthquake while others depend on the amount of seismic energy emitted by the earthquake. There are two popular earthquake scales.

17. What Did You Feel? The Mercalli Intensity Scale assigns an intensity or rating to measure the effects of an earthquake at a particular location. The Mercalli Intensity Scale assigns an intensity or rating to measure the effects of an earthquake at a particular location. The Mercalli Intensity of any one earthquake can be very different from place to place. This is because the amount of damage caused by an earthquake at a particular location depends on the geology of the location The population density and the methods used to construct buildings near the location are also important in the Mercalli scale. The Mercalli Intensity of any one earthquake can be very different from place to place. This is because the amount of damage caused by an earthquake at a particular location depends on the geology of the location The population density and the methods used to construct buildings near the location are also important in the Mercalli scale. Although it is an opinionated measure of earthquake size, seismologists still mail questionnaires to local residents after an earthquake asking them to rate the effects of the earthquake at their home. Although it is an opinionated measure of earthquake size, seismologists still mail questionnaires to local residents after an earthquake asking them to rate the effects of the earthquake at their home. Earthquake intensities are rated with Roman numerals ranging from I (not felt) to XII (buildings nearly destroyed). Earthquake intensities are rated with Roman numerals ranging from I (not felt) to XII (buildings nearly destroyed).

18. This Mercalli scale is from the Loma Prieta earthquake in the Santa Cruz mountains in California.

19. Dr. Quake The Richter magnitude scale was orginally developed by Charles Richter and Beno Gutenberg to make more quantitative measures of the relative sizes of earthquakes in southern California. Today, modified versions of the scale are used to measure earthquakes throughout the world. The Richter magnitude scale was orginally developed by Charles Richter and Beno Gutenberg to make more quantitative measures of the relative sizes of earthquakes in southern California. Today, modified versions of the scale are used to measure earthquakes throughout the world. Based on a scale of 1 to 10, each value represents the amount of energy released during the quake. Each value represents 10 times an increase in energy. (A magnitude 7 (M 7) earthquake is 10 times larger than an M 6 earthquake, an M 8 is 10 times larger than an M 7…) Based on a scale of 1 to 10, each value represents the amount of energy released during the quake. Each value represents 10 times an increase in energy. (A magnitude 7 (M 7) earthquake is 10 times larger than an M 6 earthquake, an M 8 is 10 times larger than an M 7…)

20. And That's Not All! Seismology, or the study of earthquakes, has many applications besides learning more about earthquakes. Seismology is used to monitor testing of nuclear weapons and has increased our knowledge of the interior of the Earth. Seismology, or the study of earthquakes, has many applications besides learning more about earthquakes. Seismology is used to monitor testing of nuclear weapons and has increased our knowledge of the interior of the Earth.

21. Atomic Shakes When international countries sign treaties banning the building and testing of nuclear weapons, they need some way of making sure that everyone is complying with the terms of the treaty. When international countries sign treaties banning the building and testing of nuclear weapons, they need some way of making sure that everyone is complying with the terms of the treaty. Seismology provides a means to monitor for nuclear explosions used to test and build weapons. This is because buried nuclear explosions create seismic waves which can be detected by seismographs. Seismology provides a means to monitor for nuclear explosions used to test and build weapons. This is because buried nuclear explosions create seismic waves which can be detected by seismographs. The challenge of modern day seismic monitoring is to be able to detect very small nuclear explosions detonated anywhere in the world. This makes the need for seismographs all over the world even more important. The challenge of modern day seismic monitoring is to be able to detect very small nuclear explosions detonated anywhere in the world. This makes the need for seismographs all over the world even more important.

22. The State of Quakes Now that we've learned a little about what causes earthquakes, we can take a closer look at some historical quakes in California. Now that we've learned a little about what causes earthquakes, we can take a closer look at some historical quakes in California. California has many active faults including the San Andreas fault which sometimes produce large earthquakes. California has many active faults including the San Andreas fault which sometimes produce large earthquakes. For this reason there is a very long history of active earthquake research in California to understand how and why earthquakes occur. For this reason there is a very long history of active earthquake research in California to understand how and why earthquakes occur.

23. The Great San Francisco Quake The Great San Francisco earthquake occurred on Apr. 18, 1906 at 5:12 a.m. and had a magnitude of 8.25 on the Richter scale. It is the largest earthquake to occur along the San Andreas fault in the last 200 years. The Great San Francisco earthquake occurred on Apr. 18, 1906 at 5:12 a.m. and had a magnitude of 8.25 on the Richter scale. It is the largest earthquake to occur along the San Andreas fault in the last 200 years.

25. 700 deaths were attributed to the earthquake, though current estimates place the death toll 3-4 times higher. Though the ground shaking only lasted some 45-60 seconds, the earthquake triggered fires throughout the city that lasted over 12 hours and destroyed much of the downtown. 700 deaths were attributed to the earthquake, though current estimates place the death toll 3-4 times higher. Though the ground shaking only lasted some 45-60 seconds, the earthquake triggered fires throughout the city that lasted over 12 hours and destroyed much of the downtown.

26. The Long Beach Quake The Long Beach Earthquake was on Mar. 10, 1933. It had a magnitude of 6.3 on the Richter scale. This earthquake occurred in the Newport- Inglewood fault, killing 115 people in Long Beach and the Los Angeles Basin. The earthquake toppled several unreinforced school buildings (fortunately the schools were not in session at the time) and led to the enactment of the Field Act mandating construction standards for California schools The Long Beach Earthquake was on Mar. 10, 1933. It had a magnitude of 6.3 on the Richter scale. This earthquake occurred in the Newport- Inglewood fault, killing 115 people in Long Beach and the Los Angeles Basin. The earthquake toppled several unreinforced school buildings (fortunately the schools were not in session at the time) and led to the enactment of the Field Act mandating construction standards for California schools

27. Loma Prieta part I The Loma Prieta earthquake of 1989 was centered in the southern Santa Cruz mountains. It was our nation's most costly natural disaster, causing over $6 billion in property damage, 62 deaths and 3,757 injuries. 41 of the deaths occurred when the double-decked section of the 880 freeway in Oakland collapsed. The Loma Prieta earthquake of 1989 was centered in the southern Santa Cruz mountains. It was our nation's most costly natural disaster, causing over $6 billion in property damage, 62 deaths and 3,757 injuries. 41 of the deaths occurred when the double-decked section of the 880 freeway in Oakland collapsed.