Structural Geology: Worked Examples

A bed is recorded as RHR strike $315^\circ$, dip $40^\circ$. Find its dip-direction azimuth and the two bearings of its undirected strike line.

A planar bed has RHR strike $045^\circ$ and true dip $30^\circ$. A vertical cut trends toward $090^\circ$. Find the signed apparent dip toward east.

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A planar fault has RHR strike $315^\circ$. Its trace in a vertical exposure directed $345^\circ$ descends at $40^\circ$. Recover its true dip and dip direction.

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A proposed straight alignment must follow a planar seam with RHR strike $000^\circ$ and true dip $25^\circ$. For this geometric exercise, the maximum absolute inclination is $10^\circ$. Find the largest acute deviation from strike and distinguish this angle limit from a percentage grade.

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Two vertical exposures intersect the same nonvertical planar bed. It descends $20^\circ$ toward east and $40^\circ$ toward north, using a common datum and north reference. Find true dip, dip direction and RHR strike.

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A nonvertical bed has a horizontal trace in a vertical section parallel to its known strike. A report divides $\tan0^\circ$ by $\sin0^\circ$ and claims that the bed must be horizontal. Assess that inference.

A vertical geological plane strikes $000^\circ$. Compare its intersection with vertical sections directed $045^\circ$ and $000^\circ$, both passing through the same reference point.

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A fault dips $60^\circ$ and undergoes $12.0\ \mathrm{m}$ of pure normal dip slip relative to a fixed footwall. Find the hanging wall's vertical and horizontal displacement components in a vertical section normal to strike.

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For the synthetic plane dipping $45^\circ$ toward azimuth $135^\circ$, determine the lower-hemisphere pole's trend, plunge and normalized radius on the stated equal-angle stereographic net.

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An idealized planar slope face dips $65^\circ$ toward $090^\circ$. A persistent discontinuity dips $45^\circ$ toward $090^\circ$. For a specified preliminary screen, assume lateral/rear releases exist, cohesion is zero, friction angle is $30^\circ$, and the adopted lateral direction window is $\pm20^\circ$. What does this screen establish?

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A planar slope face dips $60^\circ$ toward $090^\circ$. Two mapped discontinuities intersect in a line trending $120^\circ$ and plunging $35^\circ$ downward. Compare that line with the face in its own trend. Then test a second line with the same trend but plunge $58^\circ$.

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A proposed tunnel crosses folded limestone and shale near a mapped thrust fault. Mapping establishes fold shape and fault location, but younging, joint persistence, gouge properties, hydraulic connectivity, water pressures and fault activity remain unresolved. Compare three proposed decisions: declare the crest self-supporting; require relocation solely from the thrust label; or investigate the uncertainties before selecting alignment and support.