Some comments

Vertical exaggeration

• On all the profiles you’ve drawn the vertical and horizontal scales are not the same

• Whelan Cove – Canning: vertical scale is 1:5000, horizontal scale is 1:50 000

• This is ten times vertical exaggeration

This:

…should be this.

This…

…should be this.

And this…

…should be this.

Much easier to compare the shape of these two than…

… these two, even though here their vertical scales are identical.

Calculating vertical exaggeration

• Vertical exaggeration (VE) is the vertical scale divided by the horizontal scale

• Remember that scales are ratios to begin with• If vertical scale is 1:5000 and horizontal scale is

1:50000 the VE is

= (1/5000)/(1/50000) = 50000/5000 = 10• If vertical scale is 1:20000 and horizontal scale is

1:50000 the VE is

= (1/20000)/(1/50000) = 50000/20000 = 2.5

Structure Lab

Rule of Vs (vees)

• Helps in reading geological maps

• As a contact changes elevation, when viewed from overhead (map view), it shifts in the direction of dip

i.e., a contact “vees” in the direction of dip

Rule of Vs

a) Shallowly dipping contacts make “large” Vs

b) Horizontal contacts run parallel to the topographic contours

c) Steeply dipping contacts make “small” Vs

d) Vertical contacts run straight across topographic contours

Shallowly dipping contacts

Shallowly dipping contacts

Horizontal contacts

Horizontal contacts

Steeply dipping contacts

Steeply dipping contacts

Vertical contacts

Vertical contacts

Horizontal(parallel to contours)

Shallow dip(big “vees”)

Steep dip(small “vees”)

Vertical dip(runs straight across topo)

Question 1

what is the value of the contours?

Question 1

position the

contours

Question 1

draw the surface

Question 1

where do the

contacts cut the

surface?

Question 1

what is the orientation

of the contacts?

Hotizontal!!!(contacts follow

contours)

Question 1

fill the units

Question 1

finished!

At least part (a)

Question 2a

3 is younger than 2 is younger than 1

Question 2a

therefore 3 is above 2

Question 2a

and 2 is above 1

Question 2a

without any specific dip data, draw

lines to separate the

units

Question 2a

separate 3 from 2

Question 2a

separate 2 from 1

Finished!

Question 2b

let’s just focus on the

boundary between layers 2

and 3

Question 2b

what is the dip of the

boundaries?

Question 2b

“v” indicates dip to the

right

Question 2b

draw a dipping contact

Question 2b

no “v” indicates that the

contact is vertical

Question 2b

draw a vertical contact

Question 2b

complete the line…and draw the

others in the same way!

A couple of points…

• Rock units are assumed to be planar and of equal thickness throughout the area

• Wider outcrop in one place and narrower outcrop in another indicates differences in dip

• When drawing sections try to maintain thickness of units around folds.

Contacts are parallel and units maintain thickness

Block diagrams…

• See if you can work these ones out for yourself

• But ask questions

• Hint: look at the strike and dip symbols.

Dykes and faults

• This exercise is fairly intuitive• Note: we cannot tell the

absolute sense of motion on a fault thus we indicate relative motion with two “half” arrows

Strike and dip

Put strike FIRST (up to 3 digits)

Then DIP (only 2 digits)

Then DIP direction

110 / 25 NE