E&E 151 S Introductory Geology: Chapters 15.1, 15.3 - 15.4 (Geologic Structures Pt. 1) Definitive Study

Structural Geology

The study of processes within the solid Earth system focusing on how rocks react to tectonic forces generated by lithospheric plate movements.

Tectonic Forces

Forces acting primarily along plate margins that deform rocks, altering their orientation, location, and shape.

Stress

The amount of force applied per unit area on a rock body.

Strain

The resulting change in a rock's shape or volume caused by applied stress.

Compressive Stress

Squeezing forces from opposite directions that shorten or flatten rocks, typical of convergent plate boundaries.

Tensional Stress

Pull-apart forces acting in opposite directions that stretch or extend rocks, typical of divergent plate boundaries.

Shear Stress

Forces acting parallel to a plane that cause shear strain, typically occurring along active faults.

Elastic Behavior

Deformation where a material returns to its original shape once stress is removed.

Ductile (Plastic) Behavior

Deformation where rocks bend under stress without returning to their original shape, producing permanent folds.

Brittle Behavior

Deformation where rocks fracture and break, occurring near Earth's surface under low temperature and pressure.

Folds

Wavelike bends in layered rock containing alternating arches and troughs, signaling ductile deformation.

Joints

Fractures in bedrock along which essentially no shear displacement has occurred, typically pulled apart by tensional stress.

Joint Set

A group of multiple joints oriented parallel to one another.

Faults

Bedrock fractures along which relative sliding and displacement have occurred.

San Andreas Fault

A major right-lateral strike-slip fault system forming the boundary between the North American and Pacific plates.

Structural Traps

Subsurface geological configurations (such as anticlines, faults, or unconformities) that trap upward-migrating oil and natural gas beneath an impermeable layer.