Lecture 1: Introduction to Structural Geology

Introduction to Structural Geology

Structural geology studies how rocks have been deformed and what that deformation reveals about their history. It involves interpreting structures preserved in rocks to infer how they formed.

Three Complementary Approaches

• Geometry: Describes the size, shape, and orientation of geological structures in three dimensions.
• Kinematics: Reconstructs the movements and strains experienced by rock particles during deformation.
• Mechanics: Investigates how forces and rock properties produced those movements and structures.

Together, these approaches connect the strain observed in rocks with the stress that caused it.

Structural Geology and Engineering

Structural geology is largely an interpretive, historical science. Like detectives, geologists examine the final, deformed state of rocks and infer the processes that produced it. Engineering generally works in the opposite direction: it estimates how known or expected forces will affect materials that have not yet been deformed.

Types of Structural Study

• Observational: Describes structures in the field, including their geometry, orientation, relationships, and order and timing of formation.
• Experimental: Recreates structures under controlled laboratory conditions to investigate the processes that cause deformation.
• Theoretical: Uses physical laws and analytical or numerical models to reproduce the geometry and deformation of geological structures.

Scale Matters

Structural geology spans roughly 13 orders of magnitude, from submicroscopic features to global structures. The course focuses on:

• Mesoscopic scale: Outcrop-scale structures.
• Macroscopic scale: Geologic-map-scale structures.
• Regional scale: Structures that extend across broad areas.

Interpretations can change with the scale of observation. For example, layers may appear folded at one scale but prove to be broken by faults at a closer scale. This distinction matters in subsurface interpretation: features visible in an outcrop may be too small to resolve in seismic data, making them subseismic structures.

Suggested Follow-Up

Read Chapter 1 of Fossen’s Structural Geology and answer the associated questions.

Speakers and Sources

• Speaker: An unnamed lecturer or narrator.
• Sources mentioned: A cartoon used to introduce the topic and Chapter 1 of Fossen’s Structural Geology.