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
Re: Geologic Mapping C
Posted: January 29th, 2016, 5:10 pm
by Rob101101
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!
Re: Geologic Mapping C
Posted: January 29th, 2016, 5:27 pm
by kenniky
Rob101101 wrote: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.
Re: Geologic Mapping C
Posted: January 29th, 2016, 6:40 pm
by Rob101101
Funny, I was skimming through the binder from last year and nearly tossed the example process for this!
336/47?
Re: Geologic Mapping C
Posted: January 30th, 2016, 7:26 pm
by kenniky
170/47 or 350/47
Which is close enough, so it's your turn to ask a question
Re: Geologic Mapping C
Posted: January 31st, 2016, 7:58 am
by Rob101101
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.
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.
Re: Geologic Mapping C
Posted: January 31st, 2016, 12:09 pm
by Rob101101
Looks good, although the thicknesses are a little off. Regardless, Go!