Earthquakes Essay, Research Paper
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 K?be, 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 K?be,
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 K?be, 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 Mohorovi?i? 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.
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