# Lab.03.pptx - 9/8/11 3. MAPS AND CROSS SECTIONS I ...

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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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## This note was uploaded on 12/05/2011 for the course GEOLOGY 300 taught by Professor Stephenmartel during the Fall '11 term at University of Hawaii, Manoa.

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