Now a days Earthquake Engineering is the most
needed and essential part to save many lives from Earthquakes comes in many
counties. There a lot of effects of Earthquake can be seen in Nepal and its
belonging countries.
Definition
of Earthquake Engineering:
An
earthquake is a sudden slipping or movement of a portion of the Earth's crust
or plates, caused by a sudden release of stresses. Earthquake epicenters are
usually less than 25 miles below the Earth's surface and are accompanied and
followed by a series of vibrations.
What
causes earthquakes and where do earthquakes happen
The
earth has four major layers: The inner core, outer core, mantle and crust. The
crust and the top of the mantle make up a thin layer on the surface of earth.
But this layer is not a single cover, it is made up of many pieces like jigsaw
covering the surface of the earth. These keep slowly moving around each
other, slide past one another and bump into each other. These puzzle pieces
are called tectonic plates, and the edges of the plates are called the plate
boundaries. The plate boundaries are made up of many faults, and most of the
earthquakes around the world occur on these faults. Since the edges of the
plates are rough, they get stuck while the rest of the plate keeps moving.
Finally, when the plate has moved far enough, the edges unstick on one of the
faults and there is an earthquake.
Types
of earthquakes
Most
earthquakes in the world occur along the boundaries of the tectonic plates and
are called Inter-plate Earthquakes. A number of earthquakes also occur within
the plate itself away from the plate boundaries, called Intra-plate
Earthquakes.
How
are earthquakes recorded
Earthquakes
are recorded by instrument called seismographs. The
recording they made, is called a seismogram. The seismo gram
consists of two parts, a base and a weight, to held it firmly in the ground.
When an earthquake causes the ground to shake, the base of the seismograph
shakes too, but the hanging weight does not. Instead the spring or string that
it is hanging from absorbs all the movement. Thus the difference between the
moving and immovable part is recorded.
