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In these Lecture notes, Professor has tried to illustrate the following points : Structural Geology, Lines, Planes, Plunge, Trend, Compass Direction, Quadrant, Horizontal Line, Inclined Plane, Azimuth Direction
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Structural Geology
I. Basic Orientation of Lines and Planes in Structural Geology
A. Orientation of plane in space
a. planes: strike and dip b. lines: trend and plunge
a. infinite no. of parallel strike lines for any inclined plane b. data representation: azimuth direction
a. Apparent dip will always be < than true dip
B. Orientation of Lines
I. Solving Problems of Apparent Dip (Chapter 1 in lab manual, p. 1-9).
A. Problem: many outcrops are 2-D cuts in quarry walls, or road cuts
a. hence, any dip angles measured in that cut will be represented as "Apparent Dip"
(1) In structural analysis, we need to convert the apparent dip,
to true dip angle
(2) Chapter 1 outlines procedures for converting apparent dip to true dip
B. Solution Techiques
a. Drawing Terminology
(1) N.L. =North line (2) S.L. =strike line oriented relative to azimuth (3) D.L.= Dip line representing the direction of dip (perpendicular to strike) (4) C.L. =arbitrary construction line used to make geometric solutions (5) F.L. = fold line, imaginary line used as a fold axis to solve a problem in the 3rd dimension of the paper (i.e. to turn out items from below the plane of the paper).
b. Solving Apparent Dip Problem (1) known: strike = 25, apparent dip direction = 270, apparent dip angle = 40 (a) Question: what is true dip angle?
(2) Technique (a) draw north line, strike line and apparent dip line, intersecting at a common center point (b) draw a true dip line perpendicular to strike line, but not at the intersection point (c) turn apparent dip line into fold line, and draw a construction line from intersection point with angle of 40 degrees (d) draw line d, perpendicular to fold line, representing depth from surface to top of bed (e) draw a second line of length d, from from the intersection of the apparent dip and dip lines (f) turn true dip line into fold line, and draw a line from intersection of dip and strike lines, to end of line d from step e above. (g) measure the true dip using a protractor
a. Tan (T.D.) = tan (A.D.)/Sin(B)
(1) where T.D. = true dip angle, A.D. = apparent dip angle, B = acute angle between strike and apparent dip azimuth
a. see page 10 in lab manual for using nomogram.