A magnitude 7.8 earthquake struck
off Ecuador’s central coast on Saturday, April 16, 2016 at 7.00 pm. The
earthquake struck at 7 pm. It was devastating; buildings and streets collapsed,
people were killed and injured. The area that bore the brunt of the earthquake
was the coastal Manabi Province. Areas 300 miles away from the epicenter of the
earthquake felt the shock of the earthquake- Guayaquil. The center of the
earthquake is 27 kilometers (16.8 miles) southeast of the coastal town of
Muisne- US Geological Survey. As of Friday, April 22, 2016 the death toll was
587, and 8340 persons injured. 10,000 soldiers and 4600 police officers were
deployed to affected areas in a rescue effort.
Earlier, on Saturday, April 16,
2016 a 7.0 magnitude earthquake hit Kyushu Island in Japan. Before this
earthquake, a 6.2 magnitude earthquake struck the same area in Japan on
Thursday, April 14, 2016. Both earthquakes took their toll on human beings and
property.
HISTORY
The following is a table of some
recorded earthquakes in history:
|
NO
|
AREA
|
MAGNITUDE
|
DATE
|
LOSS
|
|
01
|
Valdivia, Chile.
It was felt at Hawaii,
at a distance of
435 miles
|
9.5 on the Richter
scale.
It is like 1000 atomic
bombs going off at
the same time
|
1960
|
6000 people died.
1 billion dollars’ worth of
damage.
|
|
02
|
Shaanxi, China.
Devastated an
area of 520 miles.
|
8.0 on the Richter
Scale.
|
January 23, 1556
|
Death toll: 830,000
|
|
03
|
Sumatra, Indonesia.
Shocks were felt in Maldives and
Thailand.
|
9.1 to 9.3
|
December 26, 2004
|
Death toll: 100,000-
225,000.
Damage and rescue: seven
billion dollars
|
|
04
|
Tohoku, Japan
|
9.03
|
March 11, 2011
|
15,878 lives lost
129,225 buildings
Collapsed.
Some destructions to 4
nuclear stations.
|
|
05
|
Yungay, Peru
|
7.9 to 8.0(Richter
Scale)
Intensity: VIII on the
Mercalli scale
|
May 31, 1970
|
Towns of Yungay and
Ranrahirca buried.
74,194 deaths recorded.
Entire communication
System lost.
|
PHYSICAL
STRUCTURE OF EARTH
The natural environment, as I
keep saying comprise of three main parts, the atmosphere or air, water and
earth or ground. As far as this post goes my focus should be, and is earth. To
know how earthquakes occur it is a prerequisite for one to know how the earth
is structured. The structure of the earth is layered both physically and
chemically. The main layers are the crust, mantle and core.
CRUST: The crust is the hard outer layer of Earth. Generally,
it is made up of oceanic crust (seabed) and continental crust, which is above
water. It contains solid rocks and elements such as oxygen and aluminum.
MANTLE: Beneath the crust is the layer called the
mantle. The mantle contains silicon, magnesium and oxygen. The mantle itself is
divided into three parts.
Upper Mantle- The upper
mantle is solid and forms the base of the crust. The upper mantle is formed of
hard, rough and heavy rock. The oceanic and continental plates encompass both
the crust and this upper mantle. Plate is the movement of the lithosphere. Plates
or tectonic plates are also described as very large rock slabs in the upper
layer of the earth. The outer part of
earth or crust plus the upper mantle together form the lithosphere. The
lithosphere, as it were, rides over the fluid asthenosphere.
The lithosphere is the area of earthquakes, volcanoes,
mountain development and continental drifts.
Upper Asthenosphere- The
asthenosphere is the lower part of the upper mantle. The upper asthenosphere is made up of melted
rock. It is below the lithosphere. It is sticky.
Lower Asthenosphere- The
lower asthenosphere is the layer after the upper asthenosphere.
Lower Mantle- It is the
lowest layer of the mantle.
THE CORE: The core is composed of iron and nickel. It
is divided into two parts.
Outer Core- The outer core
is liquid and is next to the lower mantle.
Inner Core- The inner core
make up the center of the Earth. It is hot and hard.
HOW
EARTHQUAKES OCCUR
Other names for earthquake are
quake, tremor or temblor. I have indicated that earthquakes etc. occur in the
lithosphere, i.e. the crust and upper mantle. The actual occurrence of
earthquake, it is believed, is associated with the plates or movements of the
crustal plates. When the plates move collisions occur. Collisions may be
between continental plates and continental plates, or between oceanic plates
and continental plates, or between oceanic plates and oceanic plates. When such
a collision occurs one plate is subducted under the other leading to the
occurrence of earthquake. A Free Dictionary definition of subduction:
(Geological Science) ….. the process of one tectonic plate sliding under
another resulting in tension and faulting in the earth’s crust with earthquakes
and volcanic eruptions.
When collision or subduction occurs pressure develops
resulting in vibrations (energy) released through the rocks to the surface of
the earth as seismic waves; that is when the shaking is felt or rupture occurs,
or both.
MEASUREMENT
Earthquakes are recorded by an
instrument called seismometer. Measurement of earthquake is based on the
strength and duration of the seismic waves. The magnitude of an earthquake is
determined by numbers on a scale called moment magnitude scale (Richter scale).
Magnitude of earthquake is graded as follows:
3 to 5 – minor
5 to 7 – moderate
7 to 8 - major
8 and above – great
GLOBAL
WARMING
Global warming is cited by
geologists as one of the reasons for the increase in the frequency and
intensity of seismic activities. The reason is that with global warming, more
ice is melting. Water that is generated from the melting puts pressure on the
earth’s tectonic plates.
SUMMARY
Earthquake is also variously known
as quake, tremor and temblor, depending on its magnitude.
Earthquake occurs in the
lithosphere of the earth, the lithosphere comprising of the crust of the earth
and the upper mantle.
Occurrence of earthquake-when
tectonic plates collide or are subducted, energy is released upwards through
the rocks causing the shaking of the earth or rupture of the earth, or both.
Cause of earthquake can be
natural or man- made.
PARTING SHOT
From the foregoing it can be
inferred that earthquake is as a result of imbalance in the earth’s tectonic
plates, natural or man-made. Earthquakes are not pleasant things, and therefore,
I do not think God will bequeath earthquake-plagued Earth as habitat to man.
Man has yet to be in harmony with the natural environment. When harmony between
man and the natural environment is clinched, there will be convergence of the
required balance.
Reference:
https://en.wikipedia.org/wiki/Earthquake
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