FREE ESSAY ON EARTH QUAKE REFERENCE FILES

EARTH QUAKE REFERENCE FILES

EARTHQUAKE REFERENCE FILES 
Earthquake, shaking of the earth's surface caused by rapid movement of the earth's rocky
outer layer. Earthquakes occur when energy stored within the earth, usually in the form
of strain in rocks, suddenly releases. This energy is transmitted to the surface of the
earth by earthquake waves. The study of earthquakes and the waves they create is called
seismology. Scientists who study earthquakes are called seismologists. (Webster's p.423)
The destruction an earthquake causes, depends on its magnitude or the amount of shaking
that occurs. The size varies from small imperceptible shaking, to large shocks felt miles
around. Earthquakes can tear up the ground, make buildings and other structures collapse,
and create tsunamis (large sea waves). Many Lives can be lost because of this
destruction. (The Road to Jaramillo p.211)
Several hundred earthquakes, or seismic tremors, occur per day around the world. A
worldwide network of seismographs detect about one million small earthquakes per year.
Very large earthquakes, such as the 1964 Alaskan earthquake, which measured 8.6 on the
Richter scale and caused millions of dollars in damage, occur worldwide once every few
years. Moderate earthquakes, such as the 1989 tremor in Loma Prieta, California
(magnitude 7.0), and the 1995 tremor in Kobe, Japan (magnitude 6.8), occur about 20 times
a year. Moderate earthquakes also cause millions of dollars in damage and can harm many
people. 
(The Road to Jaramillo p.213-215)
In the last 500 years, several million people have been killed by earthquakes around the
world, including over 240,000 in the 1976 T'ang-Shan, China, earthquake. Worldwide,
earthquakes have also caused severe property and structural damage. Good precautions,
such as education, emergency planning, and constructing stronger, more flexible
structures, can limit the loss of life and decrease the damage caused by earthquakes.
(The Road to Jaramillo p.213-215,263) 
AN EARTHQUAKES ANATOMY 
Seismologists examine the parts of an earthquake, like what happens to the earth's
surface during an earthquake, how the energy of an earthquake moves from inside the earth
to the surface, and how this energy causes damage. By studying the different parts and
actions of earthquakes, seismologists learn more about their effects and how to predict
ground shaking in order to reduce damage. (On Shifting Ground p.109-110)
Focus and Epicenter 
The point within the earth along the rupturing geological fault where an earthquake
originates is called the focus, or hypocenter. The point on the earth's surface directly
above the focus is called the epicenter. Earthquake waves begin to radiate out from the
focus and follow along the fault rupture. If the focus is near the surface between 0 and
70 km (0 and 40 mi.) deep shallow focus earthquakes are produced. If it is deep below the
crust between 70 and 700 km (40 and 400 mi.) deep a deep focus earthquake will occur.
Shallow-focus earthquakes tend to be larger, and therefore more damaging, earthquakes.
This is because they are closer to the surface where the rocks are stronger and build up
more strain. (The Ocean of Truth p.76 & The road to Jaramillo p.94-97) 
Seismologists know from observations that most earthquakes originate as shallow-focus
earthquakes and most of them occur near plate boundaries areas where the earth's crustal
plates move against each other. Other earthquakes, including deep-focus earthquakes, can
originate in subduction zones, where one tectonic plate subducts, or moves under another
plate. (The Ocean of Truth p.54-56)
I Faults 
Stress in the earth's crust creates faults places where rocks have moved and can slip,
resulting in earthquakes. The properties of an earthquake depend strongly on the type of
fault slip, or movement along the fault, that causes the earthquake. Geologists
categorize faults according to the direction of the fault slip. The surface between the
two sides of a fault lies in a plane, and the direction of the plane is usually not
vertical; rather it dips at an angle into the earth. When the rock hanging over the
dipping fault plane slips downward into the ground, the fault is called a normal fault.
When the hanging wall slips upward in relation to the bottom wall, the fault is called a
reverse fault or a thrust fault. Both normal and reverse faults produce vertical
displacements, or the upward movement of one side of the fault above the other side, that
appear at the surface as fault scarps. Strike slip faults are another type of fault that
produce horizontal displacements, or the side by side sliding movement of the fault, such
as seen along the San Andreas fault in California. Strike-slip faults are usually found
along boundaries between two plates that are sliding past each other. (Plate Tectonics
p.49-53)
II Waves 
The sudden movement of rocks along a fault causes vibrations that transmit energy through
the earth in the form of waves. Waves that travel in the rocks below the surface of the
earth are called body waves, and there are two types of body waves: primary, or P, waves,
and secondary, or S, waves. The S waves, also known as shearing waves, cause the most
damage during earthquake shaking, as they move the ground back and forth. (Plate
tectonics p.133)
Earthquakes also contain surface waves that travel out from the epicenter along the
surface of the earth. Two types of these surface waves occur: Rayleigh waves, named after
British physicist Lord Rayleigh, and Love waves, named after British geophysicist A. E.
H. Love. Surface waves also cause damage to structures, as they shake the ground
underneath the foundations of buildings and other structures.
Body waves, or P and S waves, radiate out from the rupturing fault starting at the focus
of the earthquake. P waves are compression waves because the rocky material in their path
moves back and forth in the same direction as the wave travels alternately compressing
and expanding the rock. P waves are the fastest seismic waves; they travel in strong rock
at about 6 to 7 km (4 mi.) per second. P waves are followed by S waves, which shear, or
twist, rather than compress the rock they travel through. S waves travel at about 3.5 km
(2 mi.) per second. S waves cause rocky material to move either side to side or up and
down perpendicular to the direction the waves are traveling, thus shearing the rocks.
Both P and S waves help seismologists to locate the focus and epicenter of an earthquake.
As P and S waves move through the interior of the earth, they are reflected and
refracted, or bent, just as light waves are reflected and bent by glass. Seismologists
examine this bending to determine where the earthquake originated. (Encarta 98)
On the surface of the earth, Rayleigh waves cause rock particles to move forward, up,
backward, and down in a path that contains the direction of the wave travel. This
circular movement is somewhat like a piece of seaweed caught in an ocean wave, rolling in
a circular path onto a beach. The second type of surface wave, the Love wave, causes rock
to move horizontally, or side to side at right angles to the direction of the traveling
wave, with no vertical displacements. Rayleigh and Love waves always travel slower than P
waves and usually travel slower than S waves. (The Floor of the Sea p.76-78, 112-115)
III CAUSES 
Most earthquakes are caused by the sudden slip along geologic faults. The faults slip
because of movement of the earth's tectonic plates. This concept is called the elastic
rebound theory. The rocky tectonic plates move very slowly, floating on top of a weaker
rocky layer. As the plates collide with each other or slide past each other, pressure
builds up within the rocky crust. Earthquakes occur when pressure within the crust
increases slowly over hundreds of years and finally exceeds the strength of the rocks.
Earthquakes also occur when human activities, such as the filling of reservoirs, increase
stress in the earth's crust. (Encarta 98)
ELASTIC REBOUND THEORY 
In 1911 American seismologist Harry Fielding Reid studied the effects of the April 1906
California earthquake. He proposed the elastic rebound theory to explain the generation
of earthquakes that occur in tectonic areas, usually near plate boundaries. This theory
states that during an earthquake, the rocks under strain suddenly break, creating a
fracture along a fault. When a fault slips, movement in the crustal rock causes
vibrations. The slip changes the local strain out into the surrounding rock. The change
in strain leads to aftershocks, which are produced by further slips of the main fault or
adjacent faults in the strained region. The slip begins at the focus and travels along
the plane of the fault, radiating waves out along the rupture surface. On each side of
the fault, the rock shifts in opposite directions. The fault rupture travels in irregular
steps along the fault; these sudden stops and starts of the moving rupture give rise to
the vibrations that propagate as seismic waves. After the earthquake, strain begins to
build again until it is greater than the forces holding the rocks together, then the
fault snaps again and causes another earthquake. (Plate tectonics p.56-59)
DISTRIBUTION 
Seismologists have been monitoring the frequency and locations of earthquakes for most of
the 20th century. They have found that the majority of earthquakes occur along plate
tectonic boundaries, while there are relatively few intraplate earthquakes, that occur
within a tectonic plate. The categorization of earthquakes is related to where they
occur, as seismologists generally classify naturally occurring earthquakes into one of
two categories: interplate and intraplate. Interplate earthquakes are the most common;
they occur primarily along plate boundaries. Intraplate earthquakes occur within the
plates at places where the crust is fracturing internally. Both interplate and intraplate
earthquakes may be caused by tectonic or volcanic forces. 
(Naked Earth p.134-135)
I Tectonic Earthquakes 
Tectonic earthquakes are caused by the sudden release of energy stored within the rocks
along a fault. The released energy is produced by the strain on the rocks due to movement
within the earth, called tectonic deformation. The effect is like the sudden breaking and
snapping back of a stretched elastic band. (The Ocean of truth p.122)
II Volcanic Earthquakes 
Volcanic earthquakes occur near active volcanoes but have the same fault slip mechanism
as tectonic earthquakes. Volcanic earthquakes are caused by the upward movement of magma
under the volcano, which strains the rock locally, and leads to an earthquake. As the
fluid magma rises to the surface of the volcano, it moves and fractures rock masses and
causes continuous tremors that can last up to several hours or days. Volcanic earthquakes
occur in areas that are associated with volcanic eruptions, such as in the Cascade
Mountain Range of the Pacific Northwest, Japan, Iceland, and at isolated hot spots such
as Hawaii. (Plate tectonics p.74)
LOCATIONS 
Seismologists use global networks of seismographic stations to accurately map the focuses
of earthquakes around the world. After studying the worldwide distribution of
earthquakes, the pattern of earthquake types, and the movement of the earth's rocky
crust, scientists proposed that plate tectonics, or the shifting of the plates as they
move over another weaker rocky layer, was the main underlying cause of earthquakes. The
theory of plate tectonics arose from several previous geologic theories and discoveries.
Scientists now use the plate tectonics theory to describe the movement of the earth's
plates and how this movement causes earthquakes. They also use the knowledge of plate
tectonics to explain the locations of earthquakes, mountain formation, deep ocean
trenches, and predict which areas will be damaged the most by earthquakes. It is clear
that major earthquakes occur most frequently in areas with features that are found at
plate boundaries: high mountain ranges and deep ocean trenches. Earthquakes within
plates, or intraplate tremors, are rare compared with the thousands of earthquakes that
occur at plate boundaries each year, but they can be very large and damaging. (On
shifting ground p.17-19)
Earthquakes that occur in the area surrounding the Pacific Ocean, at the edges of the
Pacific plate, are responsible for an average of 80 percent of the energy released in
earthquakes worldwide. Japan is shaken by more than 1000 tremors greater than 3.5 in
magnitude each year. The western coasts of North and South America are very also active
earthquake zones, with several thousand small to moderate earthquakes each year.
(U.S.G.S.)
Intraplate earthquakes are less frequent than plate boundary earthquakes, but they are
still caused by the internal fracturing of rock masses. The New Madrid, Missouri,
earthquakes of 1811 and 1812 were extreme examples of intraplate seismic events.
Scientists estimate that the three main earthquakes of this series were about magnitude
8.0 and that there were at least 1500 aftershocks. (The ocean of truth p.67-69)
EFFECTS 
Ground shaking leads to landslides and other soil movement. These are the main damage
causing events that occur during an earthquake. Primary effects that can accompany an
earthquake include property damage, loss of lives, fire, and tsunami waves. Secondary
effects, such as economic loss, disease, and lack of food and clean water, also occur
after a large earthquake. (On shifting ground p.47)
Ground Shaking and Landslides 
Earthquake waves make the ground move, shaking buildings and structures and causing
poorly designed or weak structures partially or totally collapse. The ground shaking
weakens soils and foundation materials under structures and causes dramatic changes in
fine-grained soils. During an earthquake, water-saturated sandy soil becomes like liquid
mud, an effect called liquefaction. Liquefaction causes damage as the foundation soil
beneath structures and buildings weakens. Shaking may also dislodge large earth and rock
masses, producing dangerous landslides, mudslides, and rock avalanches that may lead to
loss of lives or further property damage. (The road to Jaramillo p.43-45)
REDUCING DAMAGE 
Earthquakes cannot be prevented, but the damage they cause can be greatly reduced with
communication strategies, proper structural design, emergency preparedness planning,
education, and safer building standards. In response to the tragic loss of life and great
cost of rebuilding after past earthquakes, many countries have established earthquake
safety and regulatory agencies. These agencies require codes for engineers to use in
order to regulate development and construction. Buildings built according to these codes
survive earthquakes better and ensure that earthquake risk is reduced. (On shifting
ground p.56)
Tsunami early-warning systems can prevent some damage because tsunami waves travel at a
very slow speed. Seismologists immediately send out a warning when evidence of a large
undersea earthquake appears on seismographs. Tsunami waves travel slower than seismic P
and S waves in the open ocean, they move about ten times slower than the speed of seismic
waves in the rocks below. This gives seismologists time to issue tsunami alerts so that
people at risk can evacuate the coastal area as a preventative measure to reduce related
injuries or deaths. Scientists radio or telephone the information to the Tsunami Warning
Center in Honolulu and other stations.(The floor of the sea p.59)
Engineers minimize earthquake damage to buildings by using flexible, reinforced materials
that can withstand shaking in buildings. Since the 1960s, scientists and engineers have
greatly improved earthquake resistant designs for buildings that are compatible with
modern architecture and building materials. They use computer models to predict the
response of the building to ground shaking patterns and compare these patterns to actual
seismic events, such as in the 1994 Northridge, California, earthquake and the 1995 Kobe,
Japan, earthquake. They also analyze computer models of the motions of buildings in the
most hazardous earthquake zones to predict possible damage and to suggest what
reinforcement is needed. (Martin Alfred p.62)
Structural Design 
Geologists and engineers use risk assessment maps, such as geologic hazard and seismic
hazard zoning maps, to understand where faults are located and how to build near them
safely. Engineers use geologic hazard maps to predict the average ground motions in a
particular area and apply these predicted motions during engineering design phases of
major construction projects. Engineers also use risk assessment maps to avoid building on
major faults or to make sure that proper earthquake bracing is added to buildings
constructed in zones that are prone to strong tremors. They can also use risk assessment
maps to aid in the retrofit, or reinforcement, of older structures. (The ocean of truth
p.23)
In urban areas of the world, the seismic risk is greater in non-reinforced buildings made
of brick, stone, or concrete blocks because they cannot resist the horizontal forces
produced by large seismic waves. Fortunately, single-family timber-frame homes built
under modern construction codes resist strong earthquake shaking very well. Such houses
have laterally braced frames bolted to their foundations to prevent separation. Although
they may suffer some damage, they are unlikely to collapse because the strength of the
strongly jointed timber-frame can easily support the light loads of the roof and the
upper stories even in the event of strong vertical and horizontal ground motions.(On
shifting groung p.73)
Emergency Preparedness Plans 
Earthquake education and preparedness plans can help significantly reduce death and
injury caused by earthquakes. People can take several preventative measures within their
homes and at the office to reduce risk. Supports and bracing for shelves reduce the
likelihood of items falling and potentially causing harm. Maintaining an earthquake
survival kit in the home and at the office is also an important part of being prepared.
(On shifting ground p.97)
In the home, earthquake preparedness includes maintaining an earthquake kit and making
sure that the house is structurally stable. The local chapter of the American Red Cross
is a good source of information for how to assemble an earthquake kit. During an
earthquake, people indoors should protect themselves from falling objects and flying
glass by taking refuge under a heavy table. After an earthquake, people should move
outside of buildings, assemble in open spaces, and prepare themselves for aftershocks.
They should also listen for emergency bulletins on the radio, stay out of severely
damaged buildings, and avoid coastal areas in the event of a tsunami. (The floor of the
sea p.46)
In many countries, government emergency agencies have developed extensive earthquake
response plans. In some earthquake hazardous regions, such as California, Japan, and
Mexico City, modern strong motion seismographs in urban areas are now linked to a central
office. Within a few minutes of an earthquake, the magnitude can be determined, the
epicenter mapped, and intensity of shaking information can be distributed via radio to
aid in response efforts.(The floor of the sea p.18)
STUDYING EARTHQUAKES 
Seismologists measure earthquakes to learn more about them and to 
use them for geological discovery. They measure the pattern of an earthquake with a
machine called a seismograph. Using multiple seismographs around the world, they can
accurately locate the epicenter of the earthquake, as well as determine its magnitude, or
size, and fault slip properties. (Alfred Wegener & encarta 98)
I Measuring Earthquakes 
An analog seismograph consists of a base that is anchored into the ground so that it
moves with the ground during an earthquake, and a spring or wire that suspends a weight,
which remains stationary during an earthquake. In older models, the base includes a
rotating roll of paper, and the stationary weight is attached to a stylus, or writing
utensil, that rests on the roll of paper. During the passage of a seismic wave, the
stationary weight and stylus record the motion of the jostling base and attached roll of
paper. The stylus records the information of the shaking seismograph onto the paper as a
seismogram. Scientists also use digital seismographs, computerized seismic monitoring
systems that record seismic events. Digital seismographs use re-writeable, or
multiple-use, disks to record data. They usually incorporate a clock to accurately record
seismic arrival times, a printer to print out digital seismograms of the information
recorded, and a power supply. Some digital seismographs are portable; seismologists can
transport these devices with them to study aftershocks of a catastrophic earthquake when
the networks upon which seismic monitoring stations depend have been damaged. (Plate
Tectonics p.56-58, 64)
There are more than 1000 seismograph stations in the world. One way that seismologists
measure the size of an earthquake is by measuring the earthquake's seismic magnitude, or
the amplitude of ground shaking that occurs. Seismologists compare the measurements taken
at various stations to identify the earthquake's epicenter and determine the magnitude of
the earthquake. This information is important in order to determine whether the
earthquake occurred on land or in the ocean. It also helps people prepare for resulting
damage or hazards such as tsunamis. When readings from a number of observatories around
the world are available, the integrated system allows for rapid location of the
epicenter. At least three stations are required in order to triangulate, or calculate,
the epicenter. Seismologists find the epicenter by comparing the arrival times of seismic
waves at the stations, thus determining the distance the waves have traveled.
Seismologists then apply travel-time charts to determine the epicenter. With the present
number of worldwide seismographic stations, many now providing digital signals by
satellite, distant earthquakes can be located within about 10 km (6 mi.) of the epicenter
and about 10 to 20 km (6 to 12 mi.) in focal depth. Special regional networks of
seismographs can locate the local epicenters within a few kilometers. (the Ocean of
truth)
. 
All magnitude scales give relative numbers that have no physical units. The first widely
used seismic magnitude scale was developed by the American seismologist Charles Richter
in 1935. The Richter scale measures the amplitude, or height, of seismic surface waves.
The scale is logarithmic, so that each successive unit of magnitude measure represents a
tenfold increase in amplitude of the seismogram patterns. This is because ground
displacement of earthquake waves can range from less than a millimeter to many meters.
Richter adjusted for this huge range in measurements by taking the logarithm of the
recorded wave heights. So, a magnitude 5 Richter measurement is ten times greater than a
magnitude 4; while it is 10 x 10, or 100 times greater than a magnitude 3 measurement.
(The floor of the sea p.89-91)
Today, seismologists prefer to use a different kind of magnitude scale, called the moment
magnitude scale, to measure earthquakes. Seismologists calculate moment magnitude by
measuring the seismic moment of an earthquake, or the earthquake's strength based on a
calculation of the area and the amount of displacement in the slip. The moment magnitude
is obtained by multiplying these two measurements. It is more reliable for earthquakes
that measure above magnitude 7 on other scales that refer only to part of the seismic
waves, whereas the moment magnitude scale measures the total size. The moment magnitude
of the 1906 San Francisco earthquake was 7.6; the Alaskan earthquake of 1964, about 9.0;
and the 1995 Kobe, Japan, earthquake was a 7.0 moment magnitude; in comparison, the
Richter magnitudes were 8.3, 8.6, and 6.8, respectively for these tremors. (U.S.G.S.)
Earthquake size can be measured by seismic intensity as well, a measure of the effects of
an earthquake. Before the advent of seismographs, people could only judge the size of an
earthquake by its effects on humans or on geological or human-made structures. Such
observations are the basis of earthquake intensity scales first set up in 1873 by Italian
seismologist M. S. Rossi and Swiss scientist F. A. Forel. These scales were later
superseded by the Mercalli scale, created in 1902 by Italian seismologist Guiseppe
Mercalli. In 1931 American seismologists H. O. Wood and Frank Neumann adapted the
standards set up by Guiseppe Mercalli to California conditions and created the Modified
Mercalli scale. Many seismologists around the world still use the Modified Mercalli scale
to measure the size of an earthquake based on its effects. The Modified Mercalli scale
rates the ground shaking by a general description of human reactions to the shaking and
of structural damage that occur during a tremor. This information is gathered from local
reports, damage to specific structures, landslides, and peoples' descriptions of the
damage. (The road to Jaramillo p.122) 
II Predicting Earthquakes 
Seismologists try to predict how likely it is that an earthquake will occur, with a
specified time, place, and size. Earthquake prediction also includes calculating how a
strong ground motion will affect a certain area if an earthquake does occur. Scientists
can use the growing catalogue of recorded earthquakes to estimate when and where strong
seismic motions may occur. They map past earthquakes to help determine expected rates of
repetition. Seismologists can also measure movement along major faults using global
positioning satellites (GPS) to track the relative movement of the rocky crust of a few
centimeters each year along faults. This information may help predict earthquakes. Even
with precise instrumental measurement of past earthquakes, however, conclusions about
future tremors always involve uncertainty. This means that any useful earthquake
prediction must estimate the likelihood of the earthquake occurring in a particular area
in a specific time interval compared with its occurrence as a chance event. (The ocean of
truth p.29)
The elastic rebound theory gives a generalized way of predicting earthquakes because it
states that a large earthquake cannot occur until the strain along a fault exceeds the
strength holding the rock masses together. Seismologists can calculate an estimated time
when the strain along the fault would be great enough to cause an earthquake. As an
example, after the 1906 San Francisco earthquake, the measurements showed that in the 50
years prior to 1906, the San Andreas fault accumulated about 3.2 meters (10 feet) of
displacement, or movement, at points across the fault. The maximum 1906 fault slip was
6.5 meters (21 feet), so it was suggested that 50 years x 6.5 meters/3.2 meters, about
100 years, would elapse before enough energy would again accumulate to produce a
comparable earthquake. (Plate Tectonics)
Scientists have measured other changes along active faults to try and predict future
activity. These measurements have included changes in the ability of rocks to conduct
electricity, changes in ground water levels, and changes in variations in the speed at
which seismic waves pass through the region of interest. None of these methods, however,
has been successful in predicting earthquakes to date. (U.S.G.S)
Seismologists have also developed field methods to date the years in which past
earthquakes occurred. In addition to information from recorded earthquakes, scientists
look into geologic history for information about earthquakes that occurred before people
had instruments to measure them. This research field is called paleoseismology.
Seismologists can determine when ancient earthquakes occurred. (The floor of the sea
p.118)
Seismology, basically, the science of earthquakes, involving observations of natural
ground vibrations and artificially generated seismic signals, with many theoretical and
practical ramifications. A branch of geophysics, seismology has made vital contributions
to understanding the structure of the earth's interior. (Webster's) 
SEISMIC PHENOMENA 
Different kinds of seismic waves are produced by the deformation of rock materials. A
sudden slip along a fault, for example, produces both longitudinal push-pull (P) and
transverse shear (S) waves. Compressional trains of P waves, set up by an quick push or
pull in the direction of wave propagation, cause surface formations to shake back and
forth. Sudden shear displacements move through materials with slower S-wave velocity as
vertical planes shake up and down.
When P and S waves encounter a boundary such as Mohoroviei? discontinuity (Moho), which
lies between the crust and the mantle, they are partly reflected, refracted, and
transmitted, breaking up into several other types of waves as they pass through the
earth. Travel times depend on compressional and S-wave velocity changes as they pass
through materials with different elastic properties. Crustal granitic rocks typically
show P-wave velocities of 6 km/sec, where as underlying mafic and ultramafic rocks show
velocities of 7 and 8 km/sec. In addition to P and S waves-body-wave types-two surface
seismic waves are the Love waves, named for the British geophysicist Augustus E. H. Love,
and Rayleigh waves, named after the British physicist John Rayleigh. These waves travel
fast and are guided in their propagation by the earth's surface. (Plate Tectonics p.142)
INTRAMENTS OF STUDY 
Longitudinal, transverse, and surface seismic waves cause vibrations at points where they
reach the earth's surface. Seismic instruments have been designed to detect these
movements through electromagnetic or optical methods. The main instruments, called
seismographs, were perfected following the development by the German scientist Emil
Wiechert of a horizontal seismograph about the turn of the century. (Naked Earth
p.36-42)
Some instruments, such as the electromagnetic pendulum seismometer, employ
electromagnetic recording; that is, induced tension passes through an electric amplifier
to a galvanometer. A photographic recorder scans a rapidly moving film, making sensitive
time-movement registrations. Refraction and reflection waves are usually recorded on
magnetic tapes, which are readily adapted to computer analysis. Strain seismographs,
employing electronic measurement of the change in distance between two concrete pylons
about 30 m (100 ft.) apart, can detect compressional and extensional responses in the
ground during seismic vibrations. The Benioff linear strain seismograph detects strains
related to tectonic processes, those associated with propagating seismic waves, and tidal
yielding of the solid earth. Still more recent inventions used in seismology include
rotation seismographs; tiltmeters; wide frequency band, long-period seismographs; and
ocean bottom seismographs. (Alferd Wegener p.118-120)
Similar seismographs are deployed at stations around the world to record signals from
earthquakes and underground nuclear explosions. The World Wide Standard Seismograph
Network (WWSSN) incorporates some 125 stations. (U.S.G.S.)
Richter Who?
Richter, Charles (1900-1985), American seismologist who wrote fundamental seismology
texts, and who established an earthquake magnitude scale with German-American
seismologist
BenoGutenberg. (Encarta 98)
Richter was born in Ohio but moved to Los Angeles as a child. He attended Stanford
University and received his undergraduate degree in 1920. In 1928 he began work on his
Ph.D. in theoretical physics from the California Institute of Technology (Caltech), but
before he finished it, he was offered a position at the Carnegie Institute of Washington.
At this point, he became fascinated with seismology. After he worked at the new
Seismological Laboratory in Pasadena, under the direction of Beno Gutenberg. In 1932
Richter and Gutenberg developed a standard scale to measure the relative sizes of
earthquake sources, called the Richter scale. In 1937 he returned to Caltech, where he
spent the rest of his career, eventually becoming professor of seismology in 1952.
Richter and Gutenberg also worked to locate and catalog major earthquakes and used them
to study the deep interior of the earth. Together they wrote a very influential textbook,
published in 1954, called Seismicity of the Earth. In 1958 Richter published the
textbook, Elementary Seismology, which many consider his greatest contribution to the
field. Richter visited Japan on a Fulbright Fellowship in 1959-1960. (Encarta 98)
Richter was also involved in public awareness and safety issues surrounding earthquakes,
taking a sensible stance rather than using scare tactics. He was devoted to his work in
science and learned several languages in order to read the global earthquake literature.
Richter was so interested in earthquakes, he even installed a seismograph in his living
room of his Los Angeles home. He influenced Los Angeles building codes that city
officials credited with saving many lives in the 1971 earthquake in San Fernando,
California. After retirement he continued to work on earthquake safety design. (Encarta
98) 
(PUT MONTH) EARTHQUAKE FINDINGS 
During the month of march we charted all of the bigger earthquakes that occurred . We
charted the earthquakes measuring from 4 to 7 on the Richter scale. We plotted this data
to see where most of the earthquakes would occur. Also to see how high most of the quakes
would be on the scale.
According to our analyses most of the earthquakes occurred around the plate boundaries. 
Especially in South America along the South American plate and Mexico along the North
American plate. Yet, to our surprise there weren't many earthquakes whatsoever, along the
boundary between the Eurasian plate and the African plate. We also found Seismic activity
in some unusual areas like the arctic region above Europe and the Antarctic region. Most
of the quakes we recorded were not generally large either. Most of them were recorded at
4 on the Richter scale. There were not many large earthquakes in the month of March. The
largest quake we recorded was 6.8 in Xizang-India border region. We also found that there
were an unusually high number of earthquakes in the month of March. From the data that we
collected we noticed that earthquakes can also occur in the middle of the ocean.
In conclusion from the data we have constructed we came to find out that large
earthquakes are rare and far in between. We have come to realize how devastating
earthquakes can really be to people and their surroundings. 
REFERENCES
Kidd, J.S. & Kidd, R. A. (1997). On shifting ground "the story of continental drift". New

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