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SCI 245 Earthquakes WK 3.




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Earthquakes 1
Axia College

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Earthquakes 2
Earthquakes are defined as a series of vibrations found in the earth’s crust including
rupture and the rebound of rocks. Some may define it as the Earth releasing stress, causing a
sudden movement of the crust. This “stress” may be caused by volcanoes or other geologic
faults. Shock waves are generated by the movement of rock masses deep within the crust of the
Earth, usually near tectonic plates, which are also common causes of earthquakes. A plate
margin is known as the meeting place of one plate with another plate. There are two different
types of plate margins, which are convergent margins and divergent margins. Convergent
margins are boundaries in which two plates move towards one another and come together
(Murck, Skinner, and Mackenzie 2008). This can lead to different types of margins, depending
on whether the boundary is between two oceanic plates, two continental plates, or one of each.
Divergent margins are the opposite, as they are boundaries along which two plates are moving
apart (Murck, et al. 2008). They are liable to occur in oceanic crust, as well as continental.
Earthquakes are found to be more common along these plate margins and are shown as the most
active plate margins. An earthquake may occur at either plate margin, and a volcano may be
found among both of the plate margins.
Quake and Shake
For the most part, earthquakes are found to be caused by the abrupt movement of the
Earth’s crust along a fault line (Murck, et al., 2008, p118). If the rocks were to slide past one
another causing a collision, catastrophic earthquakes such as the Sumatra-Andaman would not
take place. It is uncommon for rocks to avoid collision and slide easily past one another.
“Friction between blocks of rocks, cause them to tighten up and grab on to one another, bringing
the motion along the part of the fault to a complete stop” (Murck, et al., 2008. p118). When the

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Earthquakes 3
fault remains locked up due to the friction, energy persists and builds up. This is referred to as a
plate motion. Plate motion causes the rocks that are next to each other to twist and crimple.
Lastly, stress builds up and energy is discharged as forceful vibrations of an earthquake (Murck,
et al., 2008). Even though these vibrations are not predictable, they are measurable.
Measuring Earthquakes
There are many different types of scales to quantify the strength of an earthquake. The
most easily recognized is the Richter scale, which was developed and studied in 1935 by a man
named Charles Richter. This scale is measured by heights of waves, or seismic waves that are
recorded on a seismograph. The Richter scale is based on a logarithm scale, which means that
for every number the scale goes up, the amplitude of the vibrations recorded by a seismograph
will increase in great numbers. The majorities of the earthquakes that take place each year
usually obtain a magnitude of 2.5 or less and go unnoticed by humans. The Richter magnitude
scale is additionally used to recognize earthquakes in the negatives, along with earthquakes that
measure 10.0 and higher. Additionally, the Movement scale is used to detect earthquakes. The
Movement magnitude scale detects the agility of the earthquake by measuring the properties of
the rock and the size of the motion or rupture. What causes the major damage of an earthquake
is the shaking of the ground. This seismic wave of motion travels through the Earth’s interior
and can destroy buildings, bridges, cities, and even human lives.
Body Waves
The vibrations are called seismic waves and they are able to travel long distances. There
are two types of seismic body waves that an earthquake can create. Compression waves, or P
waves, can “pass through solids, liquids, and gases” (Murck, et al., 2008.,p129). When it comes
to swiftness, compression waves are the fastest. These types of body waves are normally the first

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Very useful material for studying!