GEOL 11 (3): STRESS

stress

force per unit area

strain

result of stress, deformation, directly proportional to stress

Brittle manner

• way to deform

• fracturing, faulting

Ductile manner

• way to deform

• tilting, stretching

Uniform stress

• also confining stress

• result: change in size

Differential stress

• Compressive stress – result:

shortening or flattening

• Tensional stress – result: stretching

or extension

• Shear stress – result: shear strain

Elastic deformation

• reversible, not permanent change

• max reaches elastic limit

Ductile deformation

• Irreversible, permanent change

• bends or folds

symmetric folds

• axial plane is vertical and divides left and right equally

asymmetric folds

• inclined

• overturned or recumbent (flat or horizontal)

• vertical axis

Horizontal tilt of axial plane

horizontal fold, plunging fold

anticline

• convex up

• center is the oldest

• antiform - A shape

syncline

• concave up

• center is youngest

• U shape

Brittle deformation

• Permanent change

• Example: fractures, joints, faults

faults

fracture showing displacement

dip slip fault

hanging wall&foot wall shows vertical displacement based on movement

a) Normal fault (hwall moves downwards)

b) Reverse fault (>45⁰)

c) Thrust fault (<45⁰)

Strike-slip faults

a) Left-lateral or sinistral - farther block moves to the left

b) Right-lateral or dextral

oblique-slip faults

combines dip-slip and strike-slip

dome

• central uplift

• y at sides

• o at center

basin

• central sinking

• o at sides

• y at center