Geological structures

Question 1

geo structures

Answer 1

natural phenomena of deformed or fractured rock units (strata) in 3D

Question 2

geology goals (geo structures)

Answer 2

use measurements of rocks to find the history of a deformation and to understand the stress fields causing it

Question 3

geo engineering goals (geo structures)

Answer 3

use measurements to find stability of deformation, and to predict the future stability

Question 4

fold

Answer 4

• ben or curved rock strata

- formed due to plastic deformation

Question 5

fold belt

Answer 5

• set of folds distributed on a regional scale

- common with orogenic zones (mtns)

Question 6

Components of a fold       
                 axial surface
                       -|-
                     / -|- \
                   / /     \ \   limb
                       hinge line    
fold axis runs parallel the plain of the fold

Answer 6

look at pics for better description

Question 7

types of folds

Answer 7

-Anticline: upside down U
-Syncline: U
-plunging fold: fold starts out horizontal than the fold axis comes to an angle with the ground called the “angle of plunge”
-basin: dish-like
-dome: …..
-monocline: slight step down in elevation
_________
_____/

Question 8

horse mountain (He Lan Shan)
Chongqing & 3 Gorges

Answer 8

mountains with numerous folds in China

Question 9

Fault

Answer 9

• planar fracture in a rock
• the rock one side moved with respect to the other.
• can be small to tectonic plate boundaries size

Question 10

fault zone

Answer 10

series of faults in a zone with complex deformation

Question 11

Components of a fault

Answer 11

• slip vector: direction of slipping strata
• footwall: the strata that doesn’t move
• hanging wall: strata that does move

Question 12

types of faults

Answer 12

• normal: where hanging wall slides down decline
• reverse/thrust: hanging wall is pushed up incline
• shear/tear/strike-slip: no change in elevation, just slipping strata passed each other

Question 13

types of strike slip faults

Answer 13

• sinistral/left-lateral: when viewed from above, strata make ccw motion
• dextral/right-lateral: when viewed from above, makes cw motion

Question 14

series of faults

Answer 14

• step faults: look like stairs
• block faults: misaligned block shaped faults
• horse/rift valley or graben: trapezoid shaped strata that form valleys above ground

Question 15

slickensided fault surface

Answer 15

• smoothly polished surface caused by frictional movement between rocks along the two sides of a fault
• striations are the lines in the direction of the sliding on the fault face.

Question 16

Tension Crack

Answer 16

-opening in the rock due to tensile failure in slope with downward displacement

Question 17

joints

Answer 17

• planar discontinuities in rock that show or have fracture that aren’t displace with respect to each other
• slight displacement can occur

Question 18

fissures

Answer 18

• microscopic cracks in rocks that are smaller than joints

- usually don’t have pattern

Question 19

loading conditions for geo structures

Answer 19

look at page q07-8-9

Question 20

geo structures in HK

Answer 20

-Fault shown in cliff at ma shi chau

Question 21

geo structure engineering considerations

Answer 21

• geo structures are internal weaknesses of rocks and sites of penetration/ground water to screw up other foundational sites
• principal stresses are essential for cave/tunnel making

Question 22

geo structure types

Answer 22

fold
fault
fracture
joint 
fissure