Inrtoduction
Causes of
earthquakes
Severness of
earthquakes (measured strength of earthquakes)
Occurance of
earthquakes(where and when earthquakes can
happen)
Conclusion
Earthquakes are sudden movements of the Earth's surface, caused by the release of stress. Many may wonder where does this stress come from? Well the Earth is constantly moving within itself. Plates, known as tectonic plates, currently move over, under and past each other beneath the Earth's crust. Some of the plates lock together, but also continue to move against each other. This continual force is the stress that causes many earthquakes. Earthquakes can also occur from a volcanic eruption, or manmade explosions, but are not the most destructive.
Causes:
People have known about
earthquakes for thousands of years, but not very much. Today we
can pinpoint the cause of many earthquakes. As stated before,
many earthquakes are caused by stress being released among
tectonic plates. This stress can be observed over many years at
an earthquake's fault line.[Fault line is the area of deformation
of Earth's surface to which stress is being applied.] As the two
sides of the line continue to press against each other they
continually deform until a snap occurs, relieving the stress and
causing an earthquake. It was Bunjiro Koto, a geologist in Japan
studying a 60 mile long fault line whose two sides shifted about
15 feet in the great Japanese earthquake of 1871, who first
suggested that earthquakes were caused by faults.
Faults can be divided
into three main groups: Normal (tension), Thrust (compression)
and Strike Slip (shear). Many normal faults are considered to
have tensional stress for they occur in response to pulling or
tension. This is when two tectonic plates separate causing
overlying blocks to dip into the gap and resulting in an
earthquake. Thrust faults can be considered the exact opposite of
normal faults. Here the tectonic plates squeeze together or
compress until one is able to slip past the other. In this
slippage, one plate goes up towards the surface and one goes down
towards the core. Because one plate is sliding up it cracks the
overlaying blocks and lifts one side of the fault line above the
other side. The third type, Strike Slip faults, are caused by the
same causes of either normal faults or thrust faults, but have a
different outcome. Strike Slip faults are faults where each side
of the fault line moves past each other horizontally.
Severness:
Severity of such
earthquakes can vary. It mostly depends on where the energy of an
earthquake originates. If the focal point [origin of an
earthquake's energy] of an earthquake is about 70 kilometers
(43.5 miles) or less, then it is considered as a weak earthquake.
As the focal point grows between 70 to 300 kilometers (43.5 to
186 miles), the earthquake becomes intermediate. Now the deepest
or most severe earthquakes have focal points of 700 kilometers
(435 miles) or more. The ironic part of all of this is that these
depths are considered shallow compared to the depth of the
Earth's core.
An earthquake's
severity is also determined by the amount of energy released.
Today we can measure the amount of energy released in an
earthquake with a Richter Magnitude Scale. The scale was
developed in 1935, by Charles F. Richter of the California
Institute of Technology. {The Richter Scale works by determining
the logarithm of the amplitude of waves recorded by seismographs,
compensating for variation distance between seismographs and
epicenter of earthquakes, and displays the results in numbers and
decimals.} Earthquakes not felt by people are called micro
earthquakes, and have a magnitude of 2.0 or less on the Richter
Scale. Most earthquakes felt by people are in the range of 4.5 or
greater. Massive, and the most destructive earthquakes are 8.0 or
more. Also there are earthquakes that are considered massive, but
are not felt by humans because they occur beneath the
oceans.
Occurance:
Many wonder, where
exactly do earthquakes occur and when? Well the answer to that is
anywhere and anytime. So far we know that most earthquakes occur
near the surface and at the boundaries where tectonic plates
meet. There are three types of plate boundaries: spreading zones,
transform faults and subduction zones. Spreading zones are where
molten rock rises and pushes the plates apart. Example of such
earthquakes can be found in North America and along the
mid-Atlantic ridge. Transform faults occur when plates slide past
each other. An example is the San Andreas fault along the coast
of California and Northwestern Mexico. These types of earthquakes
tend to occur at shallow depths. The last type, subduction zones
occur when one plate overrides another, pushing it downward.
Example are found along the northwest coast of the United States,
western Canada, southern Alaska, and the Aleutian Islands.
Earthquakes can also occur within tectonic plates, but this only
occur in less that 10 percent of all earthquakes.
Conclusion:
In general, there is no
solid scientific proof that an earthquake or multiple earthquakes
will cause the destruction of Earth. So far there has not been an
earthquake strong enough to even reach the earth's core. Yes
earthquakes may cause the destruction of partial life on Earth,
but not all life on Earth.