Earthquakes Essay, Research Paper
Earthquakes: Causes, Mapping, and Predicting
Throughout history, man has made many advancements.
These advancements have been made to make life easier. The one
thing man can’t do is to control Mother Nature. Mother Nature can
cause many things such as earthquakes. The causes of earthquakes
have been theorized in many ways. According to the book
Predicting Earthquakes by Gregory Vogt, the Greeks, “blamed the
earthquakes on Poseidon, god of the sea”(25). The Hindu believed
that “the earth was a platform that rested on the back of eight
great elephants. When one of the elephants grew weary, it
lowered and shook its head causing the ground above to
tremble”(Vogt 25). Margaret Poynter writes “many primitive people
thought that the earth rested upon the back of some sort of animal.
When that animal became restless, great cracks appeared in the
ground, and tall trees swayed and fell. In South America, the animal
was a whale. In Japan, it was a great black spider or giant catfish.
One ancient tribe thought that four bulls supported the earth on
their horns. To amuse themselves, they sometimes tossed it from one
to another”(6). In the same book, Poynter says “The Chinese believed
that monsters lived in the caves inside the earth. When the
creatures fought, the surface of the earth trembled (6).” “In Greece,
it was not an animal, but a titan named Atlas who was condemned
to support the world upon his shoulders. Later, about the third
century B.C., a Greek philosopher, Aristotle, had a more scientific
explanation. He thought that earthquakes occurred only when hot
air masses tried to escape from the center of the earth. Two
centuries later, Lucretius, a Roman, wrote that underground
landslides caused the earth’s surface to move”(Poynter 7).2 Last
Name
Today, scientists have found a more logical reason to
earthquakes. Scientists say almost 600 million years ago, all the
continents were connected to form a huge super continent called
Pangaea. At about 220 million years ago, Pangaea began to break
up into sub-blocks. According to the book Volcanoes, Earthquakes,
and the Formation of Continents, these sub-blocks were called
“Gondwana (which corresponds approximately to the continents of
the present southern hemisphere) and Laurasia (the northern
hemisphere)” (Kohler 15). According to Pierre Kohler, “The earth’s
surface is divided into 13 plates: seven large ones (the largest
corresponding to the Pacific) and six small ones” (18-19). The book
Earthquakes by Margaret Poynter states that a person named
Robert Mallet studied earthquakes. He made tests, drew a world
map, and recreated earthquakes only to find that rocks are being
overstressed at the faults. “A fault is the place where two plates
meet and are rubbed against each other” (Groiler Electronic
Publishing, Inc.). The book, Predicting Earthquakes, the author points
out “There are generally three kinds of faults: normal, reverse, and
strike-slip. By careful observation and measurement, geologists,
acting like detectives, can tell how much a fault moved, which part
went up, which part went down, and which way the fault moved”
(Vogt 26). “When one of the plates slip under the great amount of
stress at the fault, an earthquake occurs. The shaking we feel are
the passing of long waves” (Putnam 443). “The L-waves (long
waves) travel at slower velocities that the primary and secondary
waves. These waves make the largest squiggles on a seismograph
but their effect diminishes rapidly with distance. The L-waves are
limited to the crust” (Putnam 443). One of the two kinds of waves
are “Primary waves are a kin to sound waves, and thus produce
alternate compression and rarefaction in the medium through which
they travel much like the waves that spread out through the air in
all directions from a tuning fork” (Putnam 444). The second of the
two kinds of waves are “Secondary waves, the particles in the rock
through which the wave is traveling vibrate at right angles, or
transversely, to the direction of propagation. The velocity of
P-waves are almost twice as fast as S-waves” (Putnam 444). “A
seismologist cannot locate the epicenter (where the earthquake
took place) of an earthquake that has shown up on his
seismometer from the seismogram, or written record, alone. All the
seismogram tells him are the times when the P and S waves reach
his station, and how violent they are” (Marcus 62). Rebecca Marcus,
in her work The First Book of Volcanoes & Earthquakes, explain how
scientists locate an earthquake’s epicenter. “To locate a quake, the
seismologist first finds the difference between the time of arrival of
the P wave and that of the S wave. Let us suppose that an S wave
reaches a station in New York on a certain date at 10:30 P.M., 4
minutes and
to a table, which tells him that the epicenter is 2,000 miles away.
Although he has found its distance, he does not know its direction
from his station. “Now he needs the cooperation of at least two
other stations. Messages are sent, let us say, to a station in San
Francisco and to another in Rio de Janeiro, asking for their distance
from an earthquake that occurred on that date at eighteen
seconds past 10:25 P.M., New York time. When the seismologist
receives his answers, he learns that the epicenter was 3,800 miles
from San Francisco and 3,500 miles away from Rio de Janeiro. Using
a radius representing 2,000 miles, he draws a circle around New
York. Next , using the same scale, he draws a circle with a radius
representing 3,800 miles around Riode Janeiro. The three circles cross
at a point near the Dominican Republic. And here is the epicenter of
the earthquake” (63). To measure and identify these waves, an
invention called the seismometer was used. Rebecca Marcus tells
about the first seismograph. “The very first attempt to detect a
distant earthquake was make about A.D. 136 in China by an
inventor whose name was Chang Heng. Chang Heng’s invention
consisted of a large hollow ball standing on its base which was set
on level ground. A heavy weight was suspended inside the shell.
Around the large ball, at equal distances, were eight
open-mouthed bronze dragon heads, and on the tongue of each
was a small copper ball. A bronze open-mouthed toad stood
beneath each dragon head. The whole instrument was so arranged
that, at the slightest jarring by an earthquake wave, the suspending
weight would cause one of the balls to shoot out of the dragon’s
mouth into the toad’s mouth. Which ball shot out depended on the
nearest path of the wave” (Marcus 57). In today’s modern world,
technology would make Chang Heng’s seismometer look crude and
untrust worthy. Today’s modern seismometer looks similar but more
complicated because it involves photographic paper, a beam of
light, a mirror, and many other things. In 1935, Charles Richter
created a scale that measured earthquakes. In February 1977,
Richter’s scale was slightly revised because of the fact that there
are now more sophisticated ways of measurement and the scale
didn’t cover the higher magnitude rating. In the book Geological
Disasters, by Thomas G. Aylesworth, the author states: “There is
another method of measuring earthquakes, the modified Mercali
scale. This is a twelve-point scale of intensity that grades the quake
by describing the kinds of damage and other effects caused by it.
You might say that the Richter scale measures the actual power of
the earthquake, while the modified Mercali scale measures the
earthquake’s effect on humans. In any case, the two scales do not
give us quite the same information. Here are the twelve points that
make up the modified Mercali scale: I- Just detectable by
experienced observers when prone. Microseisms (tiny vibrations).
2-Felt by few. Delicately poised objects may sway. 3- Vibration, but
still unrecognized by many. Feeble. 4- Felt by many indoors but by
few outdoors. Moderate 5- Felt by almost all. Many awakened.
Unstable objects moved. 6-I Felt by all. Heavy objects moved. Alarm.
Strong. 7- General alarm. Weak buildings considerably damaged.
Very strong. 8- Damage general except in proofed buildings. Heavy
objects overturned. 8- Buildings shifted from foundations, collapse,
ground cracks. Highly destructive. 10- Masonry buildings destroyed,
rails bent, serious ground fissures. Devastating. 11 Few if any
structures left standing. Bridges down. Rails twisted. Catastrophic. 12
Damage total. Vibrations distort vision. Objects thrown in air. Major
catastrophe” (14-15). In the book Earthquake by Bryce Walker there
is an article that explains how to predict earthquakes. Most of the
theories involve the other planets lining up and putting great stress
on the earth which causes earthquakes. “I think that all of the oil
and soft medals that we are taking is creating friction and causing
the earthquakes in California” . In, When Nature Runs Wild, the
author states that “At the present time, man cannot predict
earthquakes. Several nations, however, have research programs
that are investigating these problems. Leaders in this field are the
United States, Japan, and the Soviet Union” (Johnson 12). The World
Book Encyclopedia, writes that “Scientists can make fairly accurate
long-term predictions of where earthquakes will occur. They know,
for example, that about 80 percent of the world’s major
earthquakes happen along a belt encircling the Pacific Ocean. This
belt is sometimes called the Ring of Fire because it has many
volcanoes, earthquakes, and other geologic activity” (Earthquakes;
Karen C. McNally 38).