Structural Geology and Plate Boundaries

Structural geology studies the architecture and processes responsible for deformation of the Earth’s crust.
It involves the analysis of geological structures like folds, faults, and joints.
These structures are created through the movement and rearrangement of the Earth’s crust over millions of years.
The primary force behind these deformations is plate tectonic movement.

Stress is the force applied to a rock; the three types are compressive, tensile, and shear.
Compressive stress is when force is applied equally from opposite directions; it’s responsible for creating folds and reverse faults.
Tensile stress pulls rock apart and can lead to normal faulting and the development of rift valleys.
Shear stress is side-to-side motion. It causes rocks to shift and slide against each other, leading to strike-slip faults.

Faults are fractures in the Earth’s crust along which movement has occurred.
Normal faults occur when the crust is being extended; one block slips downwards relative to the other.
Reverse faults occur when the crust is being compressed; one block is pushed up relative to the other.
Strike-slip faults occur under shear stress when blocks move laterally with respect to each other.

Folds are formed due to compressive forces that crumple rocks into a series of wave-like undulations.
There are three main types of folds: anticlines (upward folds), synclines (downward folds), and monoclines (one side of the fold is steeper than the other).

Plate boundaries are the locations where tectonic plates interact and large scale geological activity, such as earthquakes and volcanic eruptions, are concentrated.
Convergent boundaries occur when two plates collide; this can lead to the creation of mountain ranges, earthquake activity, and often forms a subduction zone where one plate is forced beneath the other.
Divergent boundaries occur when two plates move away from each other; this typically forms mid-ocean ridges and volcanic islands.
Transform boundaries occur when two tectonic plates slide past each other horizontally; this movement is often responsible for major earthquakes.

Earthquake focal mechanisms are diagrams made using seismic data that show the direction and type of stress that caused an earthquake.
Also known as beach balls, these diagrams can help in understanding the stress regimes at plate boundaries or other active faults.