A Discussion On Earthquakes

Perhaps Mother Nature offers no greater force than that of the earthquake.
Across the span of time, earthquakes have been recorded for their incredible
destructive forces, and their abilities to awe mankind with their unparalleled
force. Earthquakes can often strike without any notice, leveling large cities
and killing scores of innocent people. Not only can earthquakes bring harm to
society through these methods of destruction, but they can also cause millions
of dollars worth of damage to the areas they destroy, causing economic chaos.
An earthquake is a natural phenomenon, occurring throughout the history of the
world. Descriptions as old as recorded history show the significant effects
earthquakes have had on people's lives. Long before there were scientific
theories for the cause of earthquakes, people around the world created folklore
to explain them. Until recent times, science has not had a complete
understanding of how earthquakes are caused, and what can be done to predict
when they will strike. This essay will discuss how earthquakes are formed and
occur, how scientists can more accurately predict the arrival of earthquakes.
Before contemplating how earthquakes might possibly be prevented, it is
essential that the process and formation of and earthquake be understood.
Earthquakes are caused when the earth's crustal plates move, rub, or push
against each other. The earth's crust (the outer layer of the earth) is made up
of seven major plates and approximately thirteen smaller ones. The name plate
is used to describe these portions of the earth's crust because they are
literally “plates” or sections, composed of dirt and rock. These plates float
on molten lava, called magma. Since the plates are floating on magma, they can
slowly move. The place where friction occurs between plates is called a fault.
A fault is a crack in a plate or a place where two or more plates meet. An
example of a fault where two plates meet is the San Andrea's fault in California,
where the Pacific and North American plates meet. The plates are about 30
miles thick under land and can be one to five miles thick beneath the ocean.
The plates move because of convection currents. Magma has currents like the
ocean does, that move in a circular motion beneath the plates. When two plates
are pushing against each other, they are constantly building up tension on the
fault. When two plates finally slip, they release a great amount of energy in
the form of shock waves. These shock waves cause vibrations, which in turn
cause the ground around the fault line to move and shake. This phenomenon is
know as an earthquake.
Because of the incredible destructive capabilities of earthquakes,
scientists are constantly trying to devise ways to ensure their early detection.
Earth scientists have begun to forecast damaging earthquakes in California.
Although quake forecasting is still maturing, it is now reliable enough to make
official earthquake warnings possible. These warnings help government, industry,
and private citizens prepare for large earthquakes and conduct rescue and
recovery efforts in the aftermath of destructive shocks. In recent years,
earthquake forecasting has advanced from a research frontier to an emerging
science. This science is now being applied in quake-plagued California, where
shocks are closely monitored and have been studied for many years. Earthquake
forecasts declare that a temblor has a certain probability of occurring within a
given time, not that one will definitely strike. In this way they are similar
to weather forecasts. Scientists are able to make earthquake forecasts because
quakes tend to occur in clusters that strike the same area within a limited time
period. The largest quake in a cluster is called the mainshock, those before it
are called foreshocks, and those after it are called aftershocks.
In any cluster, most quakes are aftershocks. Most aftershocks are too
small to cause damage, but following a large mainshock one or more may be
powerful. Such strong aftershocks can cause additional damage and casualties in
areas already devastated by a mainshock, and also threaten the lives of rescuers
searching for the injured. In the first few weeks after the 1994 magnitude 6.7
Northridge, California, earthquake, more than 3,000 aftershocks occurred. One
magnitude 5.2 aftershock caused $7 million in damage just in electric utility
equipment in the Los Angeles area alone. The U. S. Geological Survey (USGS)
first began forecasting aftershocks following the 1989 magnitude 7.1 Loma Prieta,
California, earthquake. By studying previous earthquakes, scientists had
detected patterns in the way aftershocks decrease in number and magnitude with
time. With such knowledge, scientists can estimate the daily odds for