Chapter 5

Question 1

is a strain relaxation method
where, in principle, a sample (core or block) is extracted from a rock unit, measured, and then released so that it can freely expand.

Answer 1

Overcoring

Question 2

zones of failure of the wall of a
well that give the borehole an irregular and typically elongated shape

Answer 2

Borehole breakouts

Question 3

is about how a rock responds to stress
below the limit where strain becomes permanent

Answer 3

Elasticity

Question 4

means increasing the fluid pressure until
the rock fractures. The technique is frequently applied to
petroleum reservoirs to increase the near-well permeability

Answer 4

Hydraulic fracturing

Question 5

give information about the Earth’s immediate response to stress
release along new or preexisting fractures.

Answer 5

Earthquake focal mechanism

Question 6

the simplest general stress
model for the interior of the Earth. It is based on an idealized
situation where the rock has no shear strength (ss¼ 0).

Answer 6

lithostatic reference state

Question 7

In a rock column where the rock is porous, the lithostatic stress is distributed over the grain contact area, and
this stress is called

Answer 7

effective stress

Question 8

No real, solid rock experiences a perfectly lithostatic
reference state. Only magma and other fluids do, in which
case the term

Answer 8

hydrostatic pressure

Question 9

forms when formation fluid in porous
formations is trapped between non-permeable layers.

Answer 9

Overpressure

Question 10

Stress can be locked in and preserved after the external
force or stress field has been changed or removed, and is
then referred to

Answer 10

residual stress

Question 11

The reference states of stress discussed above relate to natural
factors such as rock density, boundary conditions (uniaxial
versus plane strain), thermal effects and the physical properties of rock. Natural deviations from a reference state are
generally caused by

Answer 11

Tectonic Stress

Question 12

is the gravitational pull exerted
by the sinking slab on the rest of the plate. It is largest for
old and cold, dense oceanic lithosphere, and negative if
light and buoyant continental crust is subducted

Answer 12

Slab Pull

Question 13

simply the push from the topographically high oceanic ridge that marks divergent plate boundaries. This
ridge rises several kilometers from the ocean floor and
thus produces a significant lateral force.

Answer 13

Ridge Push

Question 14

which is the frictional resistance
or shear force acting at the base of the lithosphere

Answer 14

basal drag

Question 15

is expected to be
particularly common along convergent plate boundaries
and major active orogenic zones.

Answer 15

thrust-fault stress regime

Question 16

are found along divergent plate boundaries, but are more pronounced in areas of active continental
rifting and extension.

Answer 16

normal fault regime stress

Question 17

measures the deformation in the material in a direction perpendicular to the direction of the applied force.

Answer 17

Poisson’s Ratio

Question 18

No real, solid rock experiences a perfectly lithostatic reference state. Only magma and other fluids do, in which case the term

Answer 18

hydrostatic pressure

Question 19

reference state is based on the boundary condition that no elongation (positive or negative) occurs in the horizontal directions.

Answer 19

Uniaxial-strain reference state

Question 20

Stress can be locked in and preserved after the external force or stress field has been changed or removed and is then referred

Answer 20

Residual stress

Question 21

stress related to plate movements and plate tectonics. Locally, however, tectonic stresses may be influenced by such things as bending of layers, e.g. ahead of a propagating fault, fault interference and other local effects.

Answer 21

tectonic stress

Question 22

is the gravitational pull exerted by the sinking slab on the rest of the plate. It is largest for old and cold, dense oceanic lithosphere, and negative if light and buoyant continental crust is subducted.

Answer 22

Slab pull

Question 23

is simply the push from the topographically high oceanic ridge that marks divergent plate boundaries. This ridge rises several kilometers from the ocean floor and thus produces a significant lateral force.

Answer 23

Ridge push

Question 24

which is the frictional resistance or shear force acting at the base of the lithosphere

Answer 24

Basal drag

Question 25

the principal stresses are all equal. Hence, the lithostatic model itself provides no differential stress to the lithosphere, regardless of depth of burial.

Answer 25

lithostatic stress