[PDF] PRINCIPLES OF GEOPHYSICS

120239_7Principles_of_Geophysics.pdf

PRINCIPLES OF GEOPHYSICS

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Albert Einstein

INTRODUCTIO

Geophysics

, Math Geophysics is the science which deals with investigating the Earth, using Exploration Geophysics, and Global Geophysics. In Global

Active Passive

Passive methods

natural occurring fields or properties of the earth. Ex. SP, Magnetotell

Active Methods

and then measure how the earth respond to the signal. Ex. DC. Resistivity, -

FUNDAMENTAL CONSIDERATIONS

- ±

THEORY OF ELASTICITY

Stress

Strainis the deformation caused in the body, and is expressed as the ratio of

Triaxial Stress

Stresses act along three orthogonal axes, perpendicular to faces of solid, e.g.

Pressure

Forces act equally in all directions perpendicular to faces of body, e.g. Change in volume of solid occurs. Associated with P wave propagation

Shear Stress

No change in volume. Fluids such as water and air cannot su Associated with S wave propagation.

Stresses on a solid in 3 dimensions

Stress F/

-

Shear stress (t) acting parallel to the surface

9 components of

For each body, it is possible to define 3

principal axes, and the principal stresses. pressure (lithostatic

Pressure = (s

Conventions for directions:

compression Stresses towards the tension(extension, dilatation) +RRNH¶V IMR +RRNH¶V IMR HVVHQPLMOO\ VPMPHV POMP VPUHVV LV SURSRUPLonal to strain. $P ORR PR PRGHUMPH VPUMLQV +RRNH¶V IMR MSSOLHV MQG M VROLG NRG\ LV said to behave At high strains: the At very high strains: a solid wil

Constant of proportionality is called the

KRXQJ¶V PRGXOXV

Elastic Moduli ( Constants )

(a) KRXQJ¶V 0RGXOXV (±

E = F / ADl / l

(±

DV / V

( c ) Shear Modulus Nj