Question 10 of 21: Question 4, Part 1: Multiple Choice

Question 4, Part 1: Multiple Choice (6 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

1) → (d) horizontally directed, compressive stresses. Folding of originally flat-lying strata requires horizontal shortening; extensional stress produces normal faulting/rifting, not folding.

2) → (d). Elastic deformation is, by definition, fully recoverable – remove the stress and the rock returns to its original shape; brittle deformation is permanent fracture, plastic/ductile deformation is permanent flow.

3) → (b) cooler temperatures and low confining pressures. Brittle (fracture) behaviour dominates near the surface where temperature and confining pressure are low; raise either one and rock increasingly deforms plastically instead.

4) → (a) once its elastic limit is surpassed. Beyond the elastic limit (yield point), strain becomes permanent (brittle fracture or ductile flow, depending on conditions) – independent of lithification state or tectonic setting per se.

5) → (a). Ductile flow is favoured by the combination of high confining pressure, elevated temperature (both typical at great depth), and slow/prolonged strain rates – exactly the conditions in the roots of active orogens, not in shallow, fast, or impact-related settings.

6) → (b). In a syncline the YOUNGEST strata occupy the trough-shaped core and the OLDER strata lie on the outer, flanking limbs; those flanking limbs dip inward, TOWARD the fold axis – matching option (b) precisely (option (d) describes an anticline: older strata in the core, dipping away from the axis).