What's Shakin'?What's Shakin'?

What are earthquakes ? Why do they occur ? What are earthquakes ? Why do they occur ? Why can't we predict them ?Why can't we predict them ?

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

Just the FactsJust the Facts

An earthquake is a sudden shaking of the An earthquake is a sudden shaking of the ground. They generate ground. They generate seismic wavesseismic waves which can be recorded on a sensitive which can be recorded on a sensitive instrument called a instrument called a seismographseismograph. .

The record of ground shaking recorded by The record of ground shaking recorded by the seismograph is called a the seismograph is called a seismogramseismogram..

A Drop of Water A Drop of Water Consider what happens when a drop of rain hits a pond of Consider what happens when a drop of rain hits a pond of

water. The drop disturbs the flat surface of the water and water. The drop disturbs the flat surface of the water and creates waves that travel outward in all directions from the creates waves that travel outward in all directions from the disturbance. These waves travel on the surface of the disturbance. These waves travel on the surface of the pond, along the interface between the water and the air. pond, along the interface between the water and the air.

Earthquakes create seismic waves which shake the ground Earthquakes create seismic waves which shake the ground as they pass. They sometimes cause buildings to topple. as they pass. They sometimes cause buildings to topple. Earthquakes create waves just like waves of water moving Earthquakes create waves just like waves of water moving across the ocean and waves of air moving across a field of across the ocean and waves of air moving across a field of wheat. wheat.

Earthquakes generate Earthquakes generate seismic waves which can seismic waves which can be detected with a be detected with a sensitive instrument called sensitive instrument called a a seismographseismograph. .

Advances in seismograph Advances in seismograph technology have increased technology have increased our understanding of both our understanding of both earthquakes and the Earth earthquakes and the Earth itself. itself.

Perhaps the earliest Perhaps the earliest seismograph was invented seismograph was invented in China A.D. 136 by a m in China A.D. 136 by a m an named Choko. an named Choko.

What is a Seismograph?What is a Seismograph?

A long, long time agoA long, long time ago This early eastern This early eastern

seismoscope consisted of a seismoscope consisted of a copper vessel with eight copper vessel with eight dragon heads attached to it, dragon heads attached to it, positioned above eight positioned above eight frogs. frogs.

Each dragon head held a Each dragon head held a ball in its mouth, which, ball in its mouth, which, when dropped due to the when dropped due to the strong shaking of an strong shaking of an earthquake, would fall into earthquake, would fall into the open mouth of the frog the open mouth of the frog directly below it. directly below it.

By noting which frogs By noting which frogs contained balls after a contained balls after a strong earthquake, it was strong earthquake, it was possible to determine how possible to determine how the Earth had moved . in the Earth had moved . in response to the earthquakeresponse to the earthquake

Getting Electric Getting Electric

Because a magnet moving inside a coil Because a magnet moving inside a coil creates a current within the coil, the creates a current within the coil, the movement of the ground during an movement of the ground during an earthquake can be converted into an earthquake can be converted into an electrical signal. electrical signal.

This signal could then be used to modify This signal could then be used to modify the projection of light onto photographic the projection of light onto photographic paper, or to move a needle across paper paper, or to move a needle across paper and trace out the wiggles of the Earth's and trace out the wiggles of the Earth's shaking. shaking.

Modern Day SeismographModern Day Seismograph

Networking Information Networking Information Beginning in the 1960s, significant strides were Beginning in the 1960s, significant strides were

made in the study of earthquakes and the Earth's made in the study of earthquakes and the Earth's structure with the deployment of the World-Wide structure with the deployment of the World-Wide Seismographic Station Network (WWSSN). This Seismographic Station Network (WWSSN). This network consists of over 120 seismographs in 60 network consists of over 120 seismographs in 60 countries. countries.

The seismographs were put in vaults or old mine The seismographs were put in vaults or old mine shafts deep in the Earth in order to make sensitive shafts deep in the Earth in order to make sensitive recordings of seimic signals free from the "noise" recordings of seimic signals free from the "noise" created by cars and other environmental factors. created by cars and other environmental factors.

This "global observatory" illustrates the international This "global observatory" illustrates the international nature of global seismology and the essential nature of global seismology and the essential cooperation in data exchange needed to study cooperation in data exchange needed to study earthquakes. earthquakes.

The Slinky and The Rope The Slinky and The Rope Earthquakes generate several kinds of seismic waves Earthquakes generate several kinds of seismic waves

including P, for "Primary" and S, for "Secondary" waves. including P, for "Primary" and S, for "Secondary" waves.

The P waves move in a motion similar to the motion The P waves move in a motion similar to the motion

of a slinkyof a slinky

S WavesS Waves S waves move in a shear motion S waves move in a shear motion

perpendicular to the direction the wave is perpendicular to the direction the wave is traveling. traveling.

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

Locatin' the Shakin' Locatin' the Shakin' Seismologists locate earthquakes by measuring the time Seismologists locate earthquakes by measuring the time

between the P and S waves in a seismogram. between the P and S waves in a seismogram. After a seismogram "feels" an earthquake, scientists After a seismogram "feels" an earthquake, scientists

compare the time difference of these waves to figure out compare the time difference of these waves to figure out how far away the earthquake is. how far away the earthquake is.

It takes at least three seismograms to locate exactly where It takes at least three seismograms to locate exactly where

the earthquake is.the earthquake is.

Under Stress Under Stress Because faults have friction, they resist Because faults have friction, they resist

the forces trying to move the pieces apart. the forces trying to move the pieces apart. As the forces build, the fault remains As the forces build, the fault remains locked and the blocks get deformed locked and the blocks get deformed because of the increasing stress. because of the increasing stress.

Eventually the stresses get so high that Eventually the stresses get so high that the fault breaks. This releases the built up the fault breaks. This releases the built up stress and allows the sides of the fault to stress and allows the sides of the fault to slide past one another. This is what we slide past one another. This is what we call an earthquake. call an earthquake.

How to Release Stress How to Release Stress You can simulate the earthquake this by You can simulate the earthquake this by

placing your hands together with your placing your hands together with your thumbs up. By pushing your hands together thumbs up. By pushing your hands together you create pressure between your hands. you create pressure between your hands.

As you try to slide your hands apart, you As you try to slide your hands apart, you create friction which stops you from sliding create friction which stops you from sliding your hands easily. Stress builds up in your your hands easily. Stress builds up in your hands and arm hands and arm

Pick a Fault, any Fault Pick a Fault, any Fault You can try and visualize by placing a deck of cards between your You can try and visualize by placing a deck of cards between your

hands with your thumbs pointed up and sliding your left hand hands with your thumbs pointed up and sliding your left hand away from you and your right hand towards you. away from you and your right hand towards you.

The cards near the center of the deck are not offset very much, The cards near the center of the deck are not offset very much, but the cards near your hands are offset much farther. but the cards near your hands are offset much farther.

In this example, your left hand represents the Pacific plate and In this example, your left hand represents the Pacific plate and your right hand represents the North American plate. The middle your right hand represents the North American plate. The middle of the deck is where the San Andreas fault would be, and the of the deck is where the San Andreas fault would be, and the outer cards represent how the motion between the Pacific and outer cards represent how the motion between the Pacific and North American plates is accommodated on faults parallel to the North American plates is accommodated on faults parallel to the San Andreas. Some of these other faults are located as far away San Andreas. Some of these other faults are located as far away as Nevada! as Nevada!

Measuring A Quake Measuring A Quake

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

What Did You Feel? What Did You Feel? The Mercalli Intensity Scale assigns an intensity or The Mercalli Intensity Scale assigns an intensity or

rating to measure the effects of an earthquake at a rating to measure the effects of an earthquake at a particular location. particular location.

The Mercalli Intensity of any one earthquake can be The Mercalli Intensity of any one earthquake can be very different from place to place. This is because the very different from place to place. This is because the amount of damage caused by an earthquake at a amount of damage caused by an earthquake at a particular location depends on the geology of the particular location depends on the geology of the location The population density and the methods used to location The population density and the methods used to construct buildings near the location are also important construct buildings near the location are also important in the Mercalli scale. in the Mercalli scale.

Although it is an opinionated measure of earthquake Although it is an opinionated measure of earthquake size, seismologists still mail questionnaires to local size, seismologists still mail questionnaires to local residents after an earthquake asking them to rate the residents after an earthquake asking them to rate the effects of the earthquake at their home. effects of the earthquake at their home.

Earthquake intensities are rated with Roman numerals Earthquake intensities are rated with Roman numerals ranging from I (not felt) to XII (buildings nearly ranging from I (not felt) to XII (buildings nearly destroyed). destroyed).

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

Dr. QuakeDr. Quake The Richter magnitude scale was orginally developed The Richter magnitude scale was orginally developed

by Charles Richter and Beno Gutenberg to make by Charles Richter and Beno Gutenberg to make more quantitative measures of the relative sizes of more quantitative measures of the relative sizes of earthquakes in southern California. Today, modified earthquakes in southern California. Today, modified versions of the scale are used to measure versions of the scale are used to measure earthquakes throughout the world. earthquakes throughout the world.

Based on a scale of 1 to 10, each value represents the Based on a scale of 1 to 10, each value represents the amount of energy released during the quake. Each amount of energy released during the quake. Each value represents 10 times an increase in energy. (A value represents 10 times an increase in energy. (A magnitude 7 (M 7) earthquake is 10 times larger magnitude 7 (M 7) earthquake is 10 times larger than an M 6 earthquake, an M 8 is 10 times larger than an M 6 earthquake, an M 8 is 10 times larger than an M 7…)than an M 7…)

And That's Not All! And That's Not All!

Seismology, or the study of Seismology, or the study of earthquakes, has many applications earthquakes, has many applications besides learning more about besides learning more about earthquakes. Seismology is used to earthquakes. Seismology is used to monitor testing of nuclear weapons monitor testing of nuclear weapons and has increased our knowledge of and has increased our knowledge of the interior of the Earth. the interior of the Earth.

Atomic Shakes Atomic Shakes When international countries sign treaties banning When international countries sign treaties banning

the building and testing of nuclear weapons, they the building and testing of nuclear weapons, they need some way of making sure that everyone is need some way of making sure that everyone is complying with the terms of the treaty. complying with the terms of the treaty.

Seismology provides a means to monitor for nuclear Seismology provides a means to monitor for nuclear explosions used to test and build weapons. This is explosions used to test and build weapons. This is because buried nuclear explosions create seismic because buried nuclear explosions create seismic waves which can be detected by seismographs. waves which can be detected by seismographs.

The challenge of modern day seismic monitoring is to The challenge of modern day seismic monitoring is to be able to detect very small nuclear explosions be able to detect very small nuclear explosions detonated anywhere in the world. This makes the detonated anywhere in the world. This makes the need for seismographs all over the world even more need for seismographs all over the world even more important. important.

The State of Quakes The State of Quakes Now that we've learned a little about Now that we've learned a little about

what causes earthquakes, we can take a what causes earthquakes, we can take a closer look at some historical quakes in closer look at some historical quakes in California. California.

California has many active faults California has many active faults including the San Andreas fault which including the San Andreas fault which sometimes produce large earthquakes. sometimes produce large earthquakes.

For this reason there is a very long For this reason there is a very long history of active earthquake research in history of active earthquake research in California to understand how and why California to understand how and why earthquakes occur.earthquakes occur.

The Great San Francisco The Great San Francisco Quake Quake

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

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

The Long Beach Quake The Long Beach Quake

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

Loma Prieta part I Loma Prieta part I

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