Geography Series - 4

Hey Guys, What’s up? In the last 3 articles, we have covered basics of Geography.

Today, we will begin with interior of Earth.

Ø  Radius of earth is 6370 Km.

Ø  2 sources tell us about earth’s interiors

o   Direct Sources –

§   Rocks at mining areas viz Gold mines in South Africa 3 km deep, “Deep Ocean Drilling Project” & “Integrated drilling ocean project” at Kola in Arctic Ocean- 12 km deep;

§  Volcanic eruptions.

o   Indirect Sources –

§  Seismic Activity,

§  Meteors,

§  Gravitation- more near poles and less at equator (as distance from center at equator is more than at the poles)

§  Magnetic Field.

o   Earthquake waves are of two types:  

Ø  Body waves generated due to release of energy at focus & move in all directions throughout body of earth. They are of two types:

o   P-waves also known as Primary Waves –

§  Faster & 1^st to arrive at surface.

§  Similar to sound waves i.e. vibrate parallel to direction of the wave.

§  Travel through solid, liquid or gaseous medium

o   S-waves or secondary waves –

§  Arrive at surface after some time.

§  Travel only through solid medium

§  Vibrate perpendicular to direction of motion.

Ø  Surface waves –

o   generated by interaction of body waves with surface of earth;

o   they are last to report on seismograph

o   Vibrate perpendicular to direction of motion.

o   Most destructive.

Emergence of Shadow Zone:

Ø  

Ø  There are some areas where waves are not reported which are known as Shadow Zones.

Ø  For each earthquake different shadow zone.

Ø  Seismographs located at any distance within 105^o from epicenter recorded arrival of both P and S waves.

Ø  Seismographs beyond 145^o recorded arrival of P waves & not S waves.

Ø  So, entire zone beyond 105^o is a shadow zone of S wave (which is little more than 40% of entire earth surface) & zone between 105^o & 145^o is a shadow zone of P waves

• Types of Earthquake

Earthquake Measurement:

1)     Ritcher Scale – measures magnitude scale i.e. energy released during the quake. It is expressed in absolute numbers, 0-10.

2)     Mercalli Scale – measures intensity scale i.e. visible damage caused. The range is from 1-12.

Ø  This was all about the Earthquake. The next article will cover Structure of the Earth & Volcanic Landforms.

Ø  Please keep posting and informing us about the series. Your feedback is important to us.

Ø  Ciao!