ASBOG - Association of State Boards of Geology Structural Geology and Tectonics Questions and Answers

Question 1

On a geologic map, a series of parallel ridges and valleys are observed.
Rock units on the map show a repeating sequence of older rocks at the core of the ridges and younger rocks in the valleys.
The beds on both sides of the ridges dip away from the ridge crests.
What structural feature does this pattern represent?

Accepted Answer

A series of plunging anticlines

Answer

A series of plunging synclines

Answer

A horst and graben sequence

Answer

An imbricate thrust system

Question 2

According to Anderson's theory of faulting, which stress regime is responsible for the formation of a normal fault?

Accepted Answer

The maximum principal stress (σ1) is vertical and the minimum principal stress (σ3) is horizontal.

Answer

The maximum principal stress (σ1) is horizontal and the minimum principal stress (σ3) is vertical.

Answer

The intermediate principal stress (σ2) is vertical, with σ1 and σ3 being horizontal.

Answer

The maximum principal stress (σ1) and intermediate principal stress (σ2) are equal and horizontal.

Question 3

A structural geologist plots the poles to bedding from numerous outcrops across a folded region onto a stereonet. The poles form a great-circle girdle. What does the pole to this great-circle girdle represent?

Accepted Answer

The trend and plunge of the fold axis

Answer

The strike of the axial plane

Answer

The dip of the steepest limb

Answer

The interlimb angle

Question 4

A geologist is working in a continental rift zone, such as the East African Rift. Which of the following combinations of structural and volcanic features would they most likely encounter?

Accepted Answer

Normal faults, horsts and grabens, and bimodal (basalt-rhyolite) volcanism.

Answer

Thrust faults, tight isoclinal folds, and andesitic stratovolcanoes.

Answer

Strike-slip faults, pull-apart basins, and widespread silicic ash-flow tuffs.

Answer

Reverse faults, nappes, and high-grade metamorphic rocks like eclogite.

Question 5

Which of the following conditions would most favor ductile deformation of a rock over brittle failure?

Accepted Answer

High temperature, high confining pressure, and slow strain rate.

Answer

Low temperature, low confining pressure, and rapid strain rate.

Answer

High temperature, low confining pressure, and rapid strain rate.

Answer

Low temperature, high confining pressure, and rapid strain rate.

Question 6

A geologic cross-section reveals older Paleozoic rocks have been thrust over younger Mesozoic rocks. What type of fault is responsible for this relationship?

Accepted Answer

A reverse fault

Answer

A growth fault

Answer

A normal fault

Answer

A strike-slip fault