Earth
quake
An earthquake is the result of a sudden release of energy
in the earth’s crust that creates seismic waves.
The seismicity, seismism or seismic activity of an area
refers to the frequency, type and size of earthquakes experienced over a period
of time.
Earthquakes are measured using observation from
seismometers.
The moment magnitude is the most common scale on which
earthquakes larger than approximately 5 are reported for the entire
globe.
The most recent large earthquake of magnitude 9.0 or
large was a 9.0 magnitude earthquake in japan In 2011(as of march 2011),and it
was the Japanese earthquake since records began.
One of the most devastating earthquake in recorded
history occurred on 23 January 1556 in the Shaanxi province, China,Killing more
than 830,000 people.
Fault or fault pane :
the surface where when two block of the earth suddenly slip past one
another
hypocenter : The
location below the earth’s surface where the earthquake starts
.Epicenter : The
location on the surface of the earth directly above the hypocenter
Types of
earthquake
There are four types of earthquakes.
1.
Tectonic earthquakes
2.
Volcanic earthquakes
3.
Collapse earthquakes
4.
Explosion earthquakes
·
Tectonic earthquakes
are the most common type of earthquake.
It may be of small or of
extremely high magnitude.
·
Volcanic earthquakes occur usually
after a volcanic activity has taken place. The magma that erupts during an
earthquake leaves a space, to fill the space left by the magma the rocks move
towards the space to fill it in, causing severe earthquake.
·
Collapse earthquakes are comparatively small
earthquakes
and they take place around underground
mines.
· The explosion earthquakes
are caused due to the nuclear explosions.
EARTHQUAKE
FORMATION
Earthquakes develop in the
crust of the earth. The crust involves the earth's surface, submarine levels,
down to the ocean floors. The inner part of the earth contains massive energy.
Some of this energy escapes through cracks and other volcanic activity, but the
bulk of it is stored within the earth’s inner part, contained in the crust.
After a period of time,
the built up energy and movement causes huge tension in the plates, and there
is massive pressure on the fault lines. This intense pressure resulting from
energy build up causes the fault lines give way, and plates move over, against
or apart from each other.
Stress in
the earth’s outer layer cause a pushing effect against the sides of the
fault. Due to this motion,
rocks slip or collide against each other releasing energy. This released energy travels in waves
through the earth’s crust and causes the shaking that we fell during an
earthquake.
Under the
surface of the earth, the two sides of a fault are constantly moving, relative
to one another. This
movement is known as a fault slip. The
movement of these two sides is not smooth and is accompanied by a gradual
build-up of elastic strain energy within the rocks along the fault.
The
location on a fault where the slip first occurs is called the hypocenter,
whereas the position directly above it on the ground surface is called the
epicenter.
EARTHQUAKES MEASURES
The
strength of an earthquake can be measured by magnitude and intensity.It is
commonly measured on the Richter Scale which is an open-ended logarithmic
scale.
Date
|
Location
|
Name
|
Magnitude
|
March 11,
2011
|
|||
February
27, 2010
|
8.8
|
||
December
26,2004
|
Indian
ocean,Sumatra
|
Indian
ocean
|
9.1-9.3
|
January,12,2010
|
Aleppo,
syria
|
Aleppo
|
Unknown
|
March 28,
2005
|
8.6 |
||
September
12, 2007
|
|
8.5
|
EFFECTS OF EARTHQUAKES
Direct Effects:
1. Ground
failures(or instabilities due to ground failures) surface faulting surface or
fault rupture, or effects of seismic waves,
Ground cracking, Liquefaction.
2. Vibrations
transmitted from the ground to the structure
Indirect Effects:
1 . Tsunamis
2 . Landslides
3 . Floods
4 . Fires
The principal cause of earthquake-induced damage is ground shaking. As
the earth vibrates, all buildings on the ground surface will respond to that
vibration in varying degrees. the effect of ground shaking on buildings is a
principal area of consideration in the design of earthquake resistant
buildings.
Ground failure
Earthquake-induced
ground failure has been observed in the form of ground rupture along the fault
zone, landslides, settlement and soil liquefaction. can occur in low
density saturated sands of relatively uniform size. The phenomenon of liquefaction
is particularly important for dams, bridges, underground pipelines, and
buildings standing on such ground
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