Mantle subdivision : In the PREM seismic model, the boundary between the upper mantle and the lower mantle is accepted at a depth of 670km, where seismic velocities and density increases. This discontinuity is related to the transition of olivine from the ringwoodite phase into the mixture of perovskite and mangnesiowustite. In the Pyrolite model, […]
Mineral Phase transition in Mantle Read More »
If composition (or physical properties) changes abruptly at some interface, then seismic wave will both reflect off the interface and refract (or bend) and they pass through the interface. Two cases of wave refraction and reflection can be recognized. Reflection : A seismic reflection is generated when a wave impinges on a change in rock
Reflection and Refraction of Seismic Waves Read More »
In adjusting to change in discharge and erodibility of it’s bed, a stream modifies it’s channel so that irregularities are minimized and the least energy is expended in the movement in of water and sediments along its course. Frequently this involves enlargement of the channel cross section by erosion or reductions of it’s dimensions through
CONCEPT OF GRADE AND GRADED STREAMS Read More »
There are various forces that act upon the plates to make them move. Three possible mechanism of plate motion – Convectional Currents :- Slab Pull :- Slab pull is thought to operate at subduction zones where the subducting oceanic plate becomes colder and denser than the surrounding mantle (gabbro metamorphosed into eclogite) and pulls the
CAUSES OF PLATE MOTION Read More »
