Unformatted text preview: 9/8/11 3. MAPS AND CROSS SECTIONS I Main Topics A Three point problems B Map interpretaCon and cross secCons 9/8/11 GG303 1 3. MAPS AND CROSS SECTIONS II Three point problems A Three non
colinear points deﬁne a plane B The line of strike is given by the bearing of a horizontal line in a plane; a horizontal line connects points of equal elevaCon. C The angle of dip is given by looking parallel to strike in a cross secCon drawn perpendicular to the line of strike. 9/8/11 GG303 2 1 9/8/11 3. MAPS AND CROSS SECTIONS 9/8/11 GG303 3 3. MAPS AND CROSS SECTIONS 9/8/11 GG303 4 2 9/8/11 3. MAPS AND CROSS SECTIONS II Three point problems (cont.) D Procedure 1
Find a line of strike for the feature of interest by ﬁnding two points on the feature at equal elevaCon (this follows from the deﬁniCon of strike). Points on opposite sides of a stream, where the feature intersects a parCcular contour line, are a good choice of points. Note the elevaCon of this line of strike. 2
Then ﬁnd a third point at a known elevaCon on the feature that is oﬀ the line of strike (e.g., where the feature intersects the stream bed). 3
The posiCons and elevaCons of these three points allow the direcCon and amount of dip to be determined graphically by orthographic projecCon or algebraically. 9/8/11 GG303 5 3. MAPS AND CROSS SECTIONS II Three point problems (cont.) D Procedure 1
Find a line of strike for the feature of interest by ﬁnding two points on the feature at equal elevaCon (this follows from the deﬁniCon of strike). Points on opposite sides of a stream, where the feature intersects a parCcular contour line, are a good choice of points. Note the elevaCon of this line of strike. 2
Then ﬁnd a third point at a known elevaCon on the feature that is oﬀ the line of strike (e.g., where the feature intersects the stream bed). 3
The posiCons and elevaCons of these three points allow the direcCon and amount of dip to be determined graphically by orthographic projecCon or algebraically. 9/8/11 GG303 6 3 9/8/11 3. MAPS AND CROSS SECTIONS
IV Map interpretaCon and cross secCons A Project structural informaCon on planes (e.g., locaCon of bedding, contacts) along lines of strike onto the plane of the cross secCon B The elevaCon of the structural informaCon is plo^ed at the appropriate elevaCon. Use the same scale in the cross secCon as the map. C Strike view cross secCons diﬀer from arbitrarily chosen cross secCons in that the lines of projecCon are straight in the strike view cross secCons but are dog
legged (bent) in the arbitrarily chosen cross secCons. D Cross secCons of the geologic structure only will not show topography, just the geologic structure 9/8/11 GG303 7 3. MAPS AND CROSS SECTIONS 9/8/11 GG303 8 4 9/8/11 3. MAPS AND CROSS SECTIONS 9/8/11 GG303 9 5 ...
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 Fall '11
 StephenMartel
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