Geologic Structures

By Jenni Weller
jenniweller@yahoo.com
Introduction to Earth Science Lab
April 4, 2002
Emporia State University

This webpage has been created on behalf of my ESU class, Introduction to Earth Science Lab. In this page I will discuss various geologic structures, or deformations of rock. These structures include: Faults, such as dip slip and strike slip, Joints, and Folds, such as anticlines and synclines. I will also discuss ways in which deformation occurs.
Faults  *  Joints  *  Folds  *  Deformation
Faults

Faults are fractures with movement along crustal blocks from applied tectonic stresses.
Faults are classified by directional movement of crustal blocks.

Dip Slip Faults
Reverse compressional movement in which the hanging wall moves upward in relation to the footwall.
Normal tensional movement in which the hanging wall moves downward relative to the footwall.

Strike Slip Faults
Movement of crustal blocks that occurs from side to side.

Click here for images of Fault Types

Joints

Joints are fractures in which there has been no movement of rocks along either side.

Folds

Folds are sedimentary rock layers that have been folded due to compressional stress. Folds can be either symmetrical or asymmetrical. An axial plane is an imaginary plane that divides folds into two symmetrical parts. The line created from the axial plane is called the axis. A horizontal fold is a fold that occurs when the axis is horizontal. A plunging fold occurs when the axis is not horizontal.

Fold Types
Anticline Layers of rock that have bent to form an arch or a dome. When viewed from the Earths surface the oldest layer of rock is in the middle progressing to the youngest layer of rock on the outside.
Syncline Layers of rock that have bent to form a bowl or basin. When viewed from the Earths surface the inner layer of rock is the youngest layer progressing to the oldest layer of rock on the outside.

Click here for images of Fold Types

Deformation

There are several factors that influence deformation. Some of these factors include: temperature, pressure, rock type, and strain rate. The variation of these factors determines whether a fault or a fold occurs.

Types of Deformation
Elastic A temporary change in shape or size that is recovered when the deforming force is removed.
Plastic A permanent change in shape or size that is never recovered.

Related Sites

USGS home page

Geological Structures

Structural Geology

References

* American River College. Geologic Structures Diagrams from a course taught by Terry J. Bouroughs. [WWW Document]. URL http://www.arc.losrios.cc.ca.us/~borougt/GeologicStructuresDiagrams.htm

* Tarbuck, E.J., & Lutgens, F.K. (2000). Earth Science (9th ed.). Upper Saddle River, NJ:Prentice Hall

* Johnston, P., Aber, S.W., Sleezer, R., & Morales, M. (2000). Introduction to Earth Science Lab.

Return to the ES 111 Student Webpages.