Essay, Research Paper: Earthquakes


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Earthquakes have plagued our lives for as long as people have inhabited the
earth. These dangerous acts of the earth have been the cause of many deaths in
the past century. So what can be done about these violent eruptions that take
place nearly with out warning? Predicting an earthquake until now has almost
been technologically impossible. With improvements in technology, lives have
been saved and many more will. All that remains is to research what takes place
before, during, and after an earthquake. This has been done for years to the
point now that a successful earthquake prediction was made and was accurate.
This paper will discuss a little about earthquakes in general and then about how
predictions are made. Earthquake, “vibrations produced in the earth's crust
when rocks in which elastic strain has been building up suddenly rupture, and
then rebound.”(Associated Press 1993) The vibrations can range from barely
noticeable to catastrophically destructive. Six kinds of shock waves are
generated in the process. Two are classified as body waves-that is, they travel
through the earth's interior-and the other four are surface waves. The waves are
further differentiated by the kinds of motions they impart to rock particles.
Primary or compressional waves (P waves) send particles oscillating back and
forth in the same direction as the waves are traveling, whereas secondary or
transverse shear waves (S waves) impart vibrations perpendicular to their
direction of travel. P waves always travel at higher velocities than S waves, so
whenever an earthquake occurs, P waves are the first to arrive and to be
recorded at geophysical research stations worldwide.(Associated Press 1993)
Earthquake waves were observed in this and other ways for centuries, but more
scientific theories as to the causes of quakes were not proposed until modern
times. One such concept was advanced in 1859 by the Irish engineer Robert
Mallet. Perhaps drawing on his knowledge of the strength and behavior of
construction materials subjected to strain, Mallet proposed that earthquakes
occurred “either by sudden flexure and constraint of the elastic materials
forming a portion of the earth's crust or by their giving way and becoming
fractured.”(Butler 1995) Later, in the 1870s, the English geologist John Milne
devised a forerunner of today's earthquake-recording device, or seismograph. A
simple pendulum and needle suspended above a smoked-glass plate, it was the
first instrument to allow discrimination of primary and secondary earthquake
waves. The modern seismograph was invented in the early 20th century by the
Russian seismologist Prince Boris Golitzyn. “His device”, using a magnetic
pendulum suspended between the poles of an electromagnet, “ushered in the
modern era of earthquake research.” (Nagorka 1989) “The ultimate cause of
tectonic quakes is stresses set up by movements of the dozen or so major and
minor plates that make up the earth's crust.”(Monastersky Oct, 95) Most
tectonic quakes occur at the boundaries of these plates, in zones where one
plate slides past another-as at the San Andreas Fault in California, North
America's most quake-prone area-or is subducted (slides beneath the other
plate). “Subduction-zone quakes account for nearly half of the world's
destructive seismic events and 75 percent of the earth's seismic energy. They
are concentrated along the so-called Ring of Fire, a narrow band about 38,600 km
(about 24,000 mi) long, that coincides with the margins of the Pacific Ocean.
The points at which crustal rupture occurs in such quakes tend to be far below
the earth's surface, at depths of up to 645 km (400 mi).” (Monastersky Dec,
95) Alaska's disastrous Good Friday earthquake of 1964 is an example of such an
event. Seismologists have devised two scales of measurement to enable them to
describe earthquakes quantitatively. “One is the Richter scale-named after the
American seismologist Charles Francis Richter-which measures the energy released
at the focus of a quake. It is a logarithmic scale that runs from 1 to 9; a
magnitude 7 quake is 10 times more powerful than a magnitude 6 quake, 100 times
more powerful than a magnitude 5 quake, 1000 times more powerful than a
magnitude 4 quake, and so on.”(Associated Press 1992) The other scale,
introduced at the turn of the 20th century by the Italian seismologist Giuseppe
Mercalli, “measures the intensity of shaking with gradations from I to XII.”
(Associated Press 1992) Because seismic surface effects diminish with distance
from the focus of the quake, the Mercalli rating assigned to the quake depends
on the site of the measurement. “Intensity I on this scale is defined as an
event felt by very few people, whereas intensity XII is assigned to a
catastrophic event that causes total destruction. Events of intensities II to
III are roughly equivalent to quakes of magnitude 3 to 4 on the Richter scale,
and XI to XII on the Mercalli scale can be correlated with magnitudes 8 to 9 on
the Richter scale.”( Associated Press 1992) Attempts at predicting when and
where earthquakes will occur have met with some success in recent years. At
present, China, Japan, Russia, and the U.S. are the countries most actively
supporting such research. “In 1975 the Chinese predicted the magnitude 7.3
quake at Haicheng, evacuating 90,000 residents only two days before the quake
destroyed or damaged 90 percent of the city's buildings. One of the clues that
led to this prediction was a chain of low-magnitude tremors, called foreshocks,
that had begun about five years earlier in the area.” (Day 1988) Other
potential clues being investigated are tilting or bulging of the land surface
and changes in the earth's magnetic field, in the water levels of wells, and
even in animal behavior. A new method under study in the U.S. involves measuring
the buildup of stress in the crust of the earth. “On the basis of such
measurements the U.S. Geological Survey, in April 1985, predicted that an
earthquake of magnitude 5.5 to 6 would occur on the San Andreas fault, near
Parkfield, California, sometime before 1993.”(Day 1988) Many unofficial
predictions of earthquakes have also been made. In 1990 a zoologist, Dr. Iben
Browning, warned that a major quake would occur along the New Madrid fault
before the end of the year. Like most predictions of this type, it proved to be
wrong. “Groundwater has also played an important part in earthquake
predictions. A peak in radon in the groundwater at Kobe, Japan 9 days before the
7.2 earthquake cause quite a stir. Radon levels peaked 9 days before the quake,
then fell below the normal levels 5 days before it hit.”(Monastersky July, 95)
In North America, the series of earthquakes that struck southeastern Missouri in
1811-12 were probably the most powerful experienced in the United States in
historical time. The most famous U.S. earthquake, however, was the one that
shook the San Francisco area in 1906, causing extensive damage and taking about
700 lives.(Nagorka 1989) The whole idea behind earthquake predicting is to save
lives. With the improvement in technology, lives have been saved. New ideas and
equipment is starting to prove to be very helpful in predicting were and when an
earthquake will strike. The time and research put into earthquake predicting has
already started to pay off. It is only a matter of time before earthquakes will
no longer be a threat to us.
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