Faults

Question 1

what is a fault

Answer 1

-a fracture (joint) or zone of fractures between two blocks of rock

-rock response to stresses, extensional, compressional and shear forces

Question 2

difference between hanging wall and footwall

Answer 2

hanging wall is the block of rock above the fault line.

footwall is the block of rock below the fault line

(basically ground/ceiling)

Question 3

types of faults

Answer 3

normal, reverse, strike-slip

Question 4

what is a normal fault

Answer 4

-also known as dip-slip

defined by downwards movement of their hanging-walls, with respect to their footwalls.

Question 5

how are normal faults formed

Answer 5

response to extensional forced

Question 6

what is a reverse fault

Answer 6

-also known as thrust fault

defined by upwards movement of their hanging-walls
to footwalls.

Question 7

how is a reverse fault formed

Answer 7

response to compressional forces

defined by upwards movement of hanging-walls to the footwalls

Question 8

strike-slip fault

Answer 8

also known as sinistral/dexrel/wrench

rocks on either side of the fault are displaced along the strike of the fault surface dominantly

may be defined as sinistral (left-moving: right-bottom) or dextral (right-moving) dependent upon the direction of movement of one side compared to the other.

Question 9

what is a fault plane

Answer 9

the flat surface of rock along which a geological fault occurs

Question 10

dips of normal and reverse faults

Answer 10

average extensional faults dip:
60 degrees to the horizontal,

average reverse faults:
about 30 degrees to the horizontal

Question 11

type of fault dips

Answer 11

-Planar faults
no systematic and progressive change in the angle of dip

locally dip may change significantly in relation to competency of strata but as a whole approximated straight line with depth average dip for the fault surface

Listric faults
get progressively shallower with depth. They may even become horizontal

know as ‘detachment’

Question 12

what is strike

Answer 12

line formed by intersection of a horizontal plane and incline surface

Question 13

type of fault strikes

Answer 13

Strike-parallel faults
concordant (towards) with the strike of the strata they cut

Dip-parallel faults
roughly perpendicular (discordant angled away) to the direction of strike of the strata they cut