Post on 03-Jan-2016
description
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