|
|
|
|
|
|
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.