Earthquake generally
occurs due to the sudden release of energy inside the earth crust.
The energy
is stored within the rock inside the earth.
When the
rock slip- off from its original position causing fault, stored energy is
released in the form of waves up to the earth.
Thus the
released waves are called seismic waves
And these
waves are responsible for shaking of the earth surface.
Generally,
tectonic earthquake occurs mostly in the tectonically active areas.
Earthquake is
a natural process which cannot be predicted to happen in any particular area.
But the
history and the past records suggests the prone areas for earthquake.
Earthquake is
mostly prone in large wide spread area in the basin of Pacific Ocean named as
"Ring of Fire".
Ring of
fire is a large area which occupies over 40000 km and mostly active in tectonic
activities like earthquake and the volcanic eruptions too.
This wide
spread areas on the glove consists countries like Chile, Bolivia, Peru,
Ecuador, USA, Costa Rica, Mexico, Canada, Russia, Japan, Indonesia, Philippines,
New Zealand and others.
This comprises
South America, North America, Asia and Antarctica forming an imaginary horse
shaped structure on the globe.
The majority
of the world's earthquakes occur in this area.
About 90%
of worlds total earthquake out of which more than 81% of large earthquakes
occur in Ring of Fire.
The main
cause of this is the active tectonic movements.
The subduction
of oceanic plates of the Pacific Ocean beneath South American plate, North
American plate, Central American Plate also with volcanic islands like Aleutian
Island is the major tectonic cause.
Apart of
this, other collision of the other smaller plates with the oceanic plates are
also the major causes for the earthquakes in this area.
The largest
earthquake till now is called Valdivia earthquake or Great Chilean earthquake (1960)
also occurred in this area.
Tectonic earthquakes
are also prone in areas of orogenic belts like Himalaya.
Active tectonic
movement of both Indian and Tibetan plates leads to continuous orogenic process
in country like Nepal of the Himalayas.
According to
the statics of Geography and Environment, altogether 1,637 earthquakes of
magnitude more than 5 occurred in 2019.
That number
of earthquakes of magnitude more than 5 recorded in 2011 was 2,481 which is the
highest number of recorded earthquake in past two decades.
Geographic Distribution of Earthquake:
Geographically, earthquakes are unevenly distributed all around the globe. As earthquake are mostly frequent in some part of the world whereas in another places it is extremely rare.
It has been observed that the most of the largest earthquake mostly occurs within two defined belts:
1) Circum-pacific Belt:
This belt generally covers the rim of Pacific ocean, and it is characterized by the maximum occurance of earthquakes.
About 80% of tectonic earthquakes massively concentrated in this belt.
This rim actually coincides with the Ring of Fire.
it follows through the Western highlands of North and South America from Cape Horn to Alaska, crosses to Asia and extends Southward along the Eastern Coast of New Zealand.
2) The Mediterranean Himalayan Seismic Belts:
This belt runs from East Asia from Atlas mountains, the Apennines he Balkan mountains, the mountain chain of Asia Minor, the Caucasus, Hindu-kush, the Himalayas, the mountain chain of Burma ans the island of Indonesia.
This seismic belts runs through the Indonesian Island to coincides with Circum-Pacific Belts in Northern Australia.
https://geologyking.blogspot.com/2020/08/magnitude-of-earthquakes.html
Seismic waves
https://geologyking.blogspot.com/2020/07/seismic-waves.html
References
"Ring of Fire – Pacific Ring of Fire"
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