## Geologic Mapping C

kenniky
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### Re: Geologic Mapping C

Last week!

Using these two apparent dips, find the true dip.

Dips : 032 36* & 082 35*
Is it
`054.7 / 38.2* ?`
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Rob101101
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### Re: Geologic Mapping C

I got the same dip, but I got
`324`

kenniky
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### Re: Geologic Mapping C

```I just used a lot of trig

[img]http://i.imgur.com/L0dSMpu.png[/img]

we assume that A is on elevation 200 and B, C, D are elevation 0 (numbers are pretty arbitrary)
AB represents 032 36* dip and AC represents 082 35* dip
AD is the perpendicular from A to BC, aka the true dip
length AB = 275.28, length AC = 285.63
angle BAC is 50* so we can use law of cosines to find BC as 237.24
area of triangle ABC = AB * AC * sin(BAC) / 2 = BC * AD / 2
we can then find AD to be 253.89 and we can then use trig to find that the dip angle = arctan(200/253.89) = [b]38.23*[/b]
We then find the direction of the dip by using triangle ABD. cos(DAB) = 253.89/275.28 ==> angle DAB = 22.73
we add this angle to the direction of A to get [b]54.73[/b] as the dip direction

This is all super inefficient so I wouldn't be surprised if there was a better way to do it, but I think the answer is correct```
`I realized that our answers are 90* apart, I think I got the dip direction while you got the strike of the plane which would explain that`
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Rob101101
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### Re: Geologic Mapping C

Oh my

There is a far simpler way of doing the problem using a stereonet, you don't get such accuracy, though.
-Plot the two lines on the stereonet
-rotate the paper until the two dots lie on the same great circle
-That curve will give you the strike and the dip

I don't know which one of us made a mistake, perhaps Magikarp can give us a third opinion?
Give us a question in the meantime, though!

kenniky
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### Re: Geologic Mapping C

Oh my

There is a far simpler way of doing the problem using a stereonet, you don't get such accuracy, though.
-Plot the two lines on the stereonet
-rotate the paper until the two dots lie on the same great circle
-That curve will give you the strike and the dip

I don't know which one of us made a mistake, perhaps Magikarp can give us a third opinion?
Give us a question in the meantime, though!
hahaha, I didn't have tracing paper handy so I decided to math it lol

Might as well do a stereonet problem though! Not a lot so far in this thread.

There is an unconformity between two beddings. The bedding above the unconformity has a pole at 285/49 and the bedding below it has a pole at 218/48. Find the original pole of the bedding below the unconformity.
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Rob101101
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### Re: Geologic Mapping C

Funny, I was skimming through the binder from last year and nearly tossed the example process for this!
`336/47?`

kenniky
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### Re: Geologic Mapping C

`170/47 or 350/47`
Which is close enough, so it's your turn to ask a question
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Rob101101
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### Re: Geologic Mapping C

We went to the CNY regionals and got 4th in geomapping! Which is strange, because we couldn't work out most of the questions...

Anyway: Sketch a geologic map of the following cross section. Include : the proper strike & dip symbol for the PiPm layer closest to the left side , the proper label for the Tsp syncline, and the symbols for each layer.

Don't worry too much about the jumble between Kp and pC. http://imgur.com/2Urygaw

Unome
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### Re: Geologic Mapping C

```I just drew straight lines for boundaries; I usually see map --> cross-section, so doing the reverse is new.
[attachment=0]Geologic map.png[/attachment]```
`Realized the syncline symbol is hard to read; the arrows are supposed to run horizontally.`
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Rob101101
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### Re: Geologic Mapping C

Looks good, although the thicknesses are a little off. Regardless, Go!