Geological structures

Question 1

Why do rocks fold and fault. define sstress and strain

Answer 1

Rocks are subject to stress and undergo strain
Faulting - when rock is brittle
Folding - when rock is hot, if squeezed on sides by plate
Stress - force per unit area
Strain - changes in shape in response to stress

Question 2

How do rocks respond to stress

Answer 2

They undergo size/shape changes called strain

Question 3

Types of stress

Answer 3

Tensional - pulling apart, ex divergen plate margins
Shear - parallel
compressional - pushing tgt

Question 4

3 ways rocks respond to stress

Answer 4

elastic - deformed body recovers when stress removed, beyond elastic limit then permenent deformed
Plastic - bends but does not go to org shape, when under high temp/pressure, makes folds
Brittle - makes fractures, ex faults, surface rocks

Question 5

Parts of a fold 4

Answer 5

anticline - arch up
Syncline - arch down
hinge line - axis of fold, on a singular layer
axial plane -A plane drawn through the crest of a fold, only through anticline

Question 6

What is a overturned/recumbent fold

Answer 6

When one of the layers folds on top of itself, fold is more than 90 degrees

Question 7

What are joints vs faults vs fractures

Answer 7

joints - rock cracks, no displacement
faults - affects whole landscape, large scale, has displacement
Fracture - more general? the other two terms are types of fractures?
But thomas says it happens on glacial ice, small scale, no displacement

Question 8

What are parts of fault and how to draw

Answer 8

hanging wall block - the top block
footwall block- bottom block
have triangles or lines with circles along surface fault line, Point to hanging wall

Question 9

How to determine eroded syncline vs anticline

Answer 9

Eroded syncline - Youngest rocks exposed, rocks get older the farther away you get
Eroded anticline - Exposed rocks older near axial plane, gets younger as you move away

Question 10

what is a normal fault, how does it move, causes

Answer 10

hangin wall moves down
caused by extension
can make graben or horst
use lines with circles and point towards hanging wall
ex rift valleys

Question 11

Graben vs horst

Answer 11

horst - block moved up relative to adjacent blocks because of faulting
Graben - block moved down relative to adj blocks bc of faulting

Question 12

What is a thrust fault vs reverese fault

Answer 12

Thrust fault is a reverse fault, but has really small angle

Question 13

What is reverse fault, how does it move,causes

Answer 13

hanging wall moves up, from compressional stress
use triangles and point towards hanging wall

Question 14

What is strike slip fault, how does it move

Answer 14

fault where movt is horz
caused by shear stress

Question 15

How do you show the angle of the layers and the fault

Answer 15

use strike and dip
T shape,
arms are horizontal to the fault
bottom of T points towards the tip
the number next to it says the angle of the dip