By: Dwight Dher Ranis Alaba

Chapter 10.

Definition: the changes of rock masses in different sizes, shape, and position.

Crustal deformation mostly occur along plate margins.

Force & Stress. Force tends to put stationary (not moving)

objects in motion or change the motion of moving objects.

Ex. When your door is stuck (stationary), you apply force to move it (get it in motion.

Cont. on next page

Structural Geologists use the term “stress” to describe the forces that deforms a rock.

The magnitude of stress also relates to the area on which the force acts, not just the amount of force applied.

Stress causes irreversible damage/change in sizes and shapes of a rock body.

Types of Stress Differential Stress – stress is applied

unequally in different directions Compression stress – plate collides to shorten

and thicken the earth’s crust.

Continuation

Cont. on next page

Tensional stress – stretches horizontally which causes rock bodies to lengthen and thin vertically.

Shear stress – displacement along fault zone or by ductile flow.

Strain Easiest type of deformation that occurs on

along small fault surfaces. Strain shows the effect of stress from the rocks. There are also different types of stresses. Elastic deformation, plastic deformation, brittle

deformation.

continuation

Types of strains Elastic deformation – rocks return to its

original shape when stress is removed. plastic stress - folding and flowing of stresses

in high temperature and pressure causes rocks to deform permanently.

Brittle deformation -