Chapter 4

Question 1

One type affects the entire volume of a rock, the outside as well as the inside

Answer 1

body forces

Question 2

Body forces define threedimensional fields. The most important type of body force in structural geology

Answer 2

gravity

Question 3

The other type of force acts on surfaces only and is referred to as

Answer 3

surface force

Question 4

Surface forces originate when one body pushes or pulls another body. The force that acts across the contact area between the two bodies
is a

Answer 4

surface force

Question 5

A stress vector oriented perpendicular to a surface is called

Answer 5

normal stress on the surface

Question 6

while a stress vector that acts parallel to a surface is referred to as

Answer 6

shear stress

Question 7

An obvious requirement for expressing
stress as an ellipse (ellipsoid) is that there is not a combination of positive and negative tractions. The ellipse
is called

Answer 7

stress ellipse and the ellipsoid id the stress ellipsoid

Question 8

its orientation tell us everything about the state of stress at a given point in a rock, or in a rock volume in which stress is homogeneous

Answer 8

stress ellipsoid

Question 9

The axes are called the principal
stresses and are the poles to the principal planes of stress. These are the only planes where the shear stress

Answer 9

zero

Question 10

It is useful to put the nine components of stress into a matrix (second-order tensor) known as

Answer 10

stress sensor or stress matrix

Question 11

is a real number, reflecting temperature, mass, density, speed or any other physical magnitude that has no direction

Answer 11

Scalar

Question 12

has both magnitude (length) and direction, such as force, traction (stress vector)
or velocity

Answer 12

Vector

Question 13

In the latter case, the elements of
the tensor are functions of position and the tensor forms what is called a ________ This simply means that the tensor is defined at every point within a region of space (or space-time),

Answer 13

Tensor field

Question 14

Any stress tensor can be split into two symmetric matrices

Answer 14

first part represents the mean stress and the second is called the deviatoric stress.

Question 15

the difference between the mean
stress and the total stress. represents the anisotropic component of the total stress

Answer 15

The deviatoric stress

Question 16

The difference between the maximum and minimum principal stresses (s1 s3) is the diameter of the circle.

Answer 16

The differential stress

Question 17

is generally limited to media with no or very low shear resistance (fluids).

Answer 17

Pressure (p)

Question 18

is used when dealing with media with a minimum of shear resistance (rocks).

Answer 18

Stress (σ)

Question 19

A stress vector oriented perpendicular to a surface is called the

Answer 19

normal stress

Question 20

A stress vector that acts parallel to a surface is referred to as the

Answer 20

shear stress

Question 21

are the principal stress vectors

Answer 21

eigenvectors

Question 22

the matrix which are the principal stresses

Answer 22

eigenvalues

Question 23

There is no shear stress “anywhere” and there is no off-diagonal stress in the total stress tensor.

Answer 23

hydrostatic stress

Question 24

n a fluid. and represents an isotropic state of stress. In the lithosphere, the mean stress is closely related to __________ (where the pressure is due to overlying rock, not fluid).

Answer 24

lithostatic pressure

Question 25

A practical graphical way of presenting and dealing with stress is based on a diagram referred to as the

Answer 25

Mohr diagram