Bring out the relevance of seismic study in determining the structure of earth's interiors
Answers
The behavior of sesmic waves in different layers of the earth provides the most authentic evidence about the composition & structure of the earth. The different types of waves generated during the occurrence of earthquake , are generally divided into 3 broad categories;-
a)Primary waves, b)Secondary waves ,c)surface waves.
Seismic Waves- both P-waves & S-waves travel faster through rigid material than through soft or plastic material.The velocities of these waves travelling through specific part of earth gives an indication of type of rocks there.Abrupt changes in seismic wave velocities indicate significant changes in earths interior.
Seismic waves passing through the earth are refracted in ways that show distinct discontinuities within earth's interior & provide basis for the belief that earth has
1)a solid inner core, 2)a liquid outer core, 3)a soft aesthenosphere, 4) a rigid lithosphere.
Seismic vibrations follow property of light waves being reflected & refracted with change in medium.
interference:-
a)NON HOMOGENEOUS- If earth were homogeneous solid, seismic waves waves would travel in straight line with a constant speed. But seismic waves arriving sooner at distant stations & later at closer stations indicate that earth is not a homogeneous , uniform mass but has physical properties that change with depth.
b)SHADOW ZONE- Refraction at the boundary between the core & the mantle thus causes a p-wave shadow zone over part of earth's surface i.e. zone where no P-waves are received between 103 & 143 deg. S- waves do not pass through the core . there is a huge shadow zone therefore outer core is liquid (as S-waves do not pass through liquid)