Tectonic earthquake generally occurs
due to the sudden release of certain amount of energy stored in the rocks
beneath the Earth’s surface. It is due to the slip off of rocks due to the
maximum stress acted on it.
So the potential energy stored in a
rock transformed into kinetic energy during the earthquake and the energy is
released in the form of waves and in case of the tectonic earthquake, these
energy waves are called seismic waves.
Seismic waves propagate in all
direction and possess their magnitude.
Magnitude:
Generally magnitude is the measure of
energy released during the earthquake.
On the basis of amplitude of seismic
waves magnitude of the earthquake is measured.
Scale:
In 1935, professor Charles Richter of California Institute of
Technology, proposed a scale to measure the magnitude of earthquake or to
indicate the energy released during an earthquake. Today it is famously known
as Richter scale or also called as magnitude scale.
The scale is a numerical value of
magnitudes from 0 to 9, where higher number indicates the larger
earthquakes.
Generally, Richter-scale is
logarithmic scale. That means it shows wide range of data. Here the scale is
numbered in steps, with each scale representing the earthquake 10 times larger
than the previous scale.
For example: if the seismograph
records the earthquake of magnitude 7 then it is 10 times larger than an
earthquake of magnitude 6 , 100 times larger than of magnitude 5 as well as
1000 times larger than an earthquake of magnitude 4.
The largest magnitude of earthquake
ever recorded was 9.6, called the great Chilean earthquake or (Valdivia
Earthquake) in 1960.
Seismograph:
Seismograph is an instrument to
measure earthquake. Generally seismograph is adjusted /mounted on the ground
surface. During an earthquake, when the ground starts to shake the suspended
mass or the case inside seismograph starts to move and it is called
seismometer.
The difference between Seismograph
and Seismometer is that seismometer is always fitted inside the seismograph.
As the seismometer works electromagnetically and hence collects the data by generating electric signal which can be subjected on the computer screen or onto the paper. Hence the obtained data is called seismogram.
Apart from this, now it has been
possible to determine the depth of the focus of the earthquake by analyzing the
seismograms.
On the basis of depth of the focus,
generally earthquake can be classified as:
a) Surface earthquakes:
When the depth of focus of the earthquake is less than 10 km it is known
as the surface earthquakes.
b) Shallow-focus earthquake:
Earthquake with focus at the depth
rising from 10km to 50 km is termed as the shallow-focus earthquake.
c) Intermediate-focus earthquake:
When the depth of the focus of the
earthquake varies from 50km to 300km then it is known as intermediate-focus
earthquake.
d)
Deep-focus earthquake:
The earthquake which originates at the
depth more than 300km is called deep-focus earthquake.
Among all of them, shallow focus
earthquake also called normal earthquake are the most occurring as it
constitutes more than 85% of total earthquakes.
Earthquake is a natural calamity and cannot be prevented.
Damage by earthquake varies with the
strength of the earthquake, subsurface bedrock and types of building
constructions.
Some important effects of earthquake
are:
a)
Collapse of engineering structures
like road, building, bridges etc.
b)
Change in the geology or simply
geological structure of a particular area due to both horizontal and vertical
movement.
c)
Landslide and subsidence of land is
also prone due to the effect of earthquake.
d)
Disturbance in the availability ground water.
e)
Also leads to other catastrophic like
Tsunamis and others.
We are living in the century of technologies
as there has been tremendous progress in the field of science.
But it has not yet become possible to
have any scientific inventions and methods for the accurate prediction of the
earthquake.
Great information
ReplyDeleteVery detailed and educative
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