Talk:Strike and dip

Equivalence of angles

"and the other value of 335 is discarded": I don't see how 335 is equivalent to 25. I think that N335W is equivalent to N25E, but that N335E is not. 132.156.40.110 (talk) 21:56, 26 January 2010 (UTC)

Bit confused by this myself (first time I've really looked at this article), it could be a lot clearer. I'm not sure that it shouldn't be 205°, rather than 335°, but maybe that's not what it's trying to say. Worth a rewrite I reckon. Mikenorton (talk) 22:22, 26 January 2010 (UTC)

Changed 335 to 205, as in versions before last February. Mikenorton (talk) 22:29, 26 January 2010 (UTC)

Apparent Dip vs. Dip

I'm confused by the notion of "apparent dip." The article doesn't seem to explain it, and the diagram isn't any help. Is apparent dip like an optical illusion, or what? Also, I would think the (true) dip would necessarily be 90 degrees to the strike (except in the case of vertical or horizontal beds, where it's presumably undefined), and at one point the article says that. But the article also says "True dip can be calculated from apparent dip using trigonometry if you know the strike" and that *seems* to imply more than just adding or subtracting 90 degrees from the strike. Do you really need trig? If so, why? Mcswell (talk) 04:58, 31 December 2014 (UTC)

You can't always lay your compass on the rock. Suppose you have drill hole data from a region for 3 holes each of which intersects a distinctive layer at different depths (elevation), the apparent dip for each pair of drill holes is obtained from the difference in elevation of the layer and direction from shallowest to deeper of each pair. From this the strike and true dip of the layer is determined with a bit of trig, assuming the layer is continuous (not faulted) and the attitude is uniform. Also the apparent dip is used for constructing cross-section diagrams that aren't perpendicular to the strike. Vsmith (talk) 14:50, 31 December 2014 (UTC)

A nifty diagram would probably help - let me think on that. You often see apparent dip in natural sections, such as quarry faces at differing angles or on cliffs. While I'm thinking about a diagram, I'll see if there any pictures around that illustrate the situation. Mikenorton (talk) 18:29, 1 January 2015 (UTC)