ROTATIONAL STRAIN

PERCENT LENGTHENING/EXTENSION (e)

REVIEW

Strain is a nonrigid body movement involving changes in shape (distortion) and size (dilation). Strain is internal deformation.

Homogeneous strain is nonrigid deformation carried out in a regular, uniform manner. Straight lines remain as straight lines. Parallel lines remain as parallel lines. For example think of homogeneous nonrigid rifting (also knwon as pure shear)
 
 

Linear strain is length change and can be the extension, % lengthening or Stretch factor.

DEFINITIONS
 
 

READINGS CH.3 CH.4

LECTURE

 Let's plot linear strain in and all its cases on a two-dimesional graph.

ROTATIONAL STRAIN

The directions of maximum and minimum extension change in orientation during the course of distortion. Simple shear is a type of rotational strain in which the volume does not change, and the deformation is homogeneous.

Analysis of homework handout
 
 

One very important way of carrying out rotational deformation is through simple shear. Ideal Simple shear provides another model for understanding how rfting takes place. Simple shear involves a very localised amount of rotational strain concentrated within a narrow fault zone. The blocks above and below fault and so make for a more realistic rifting model than the one of homogeneous nonrotational strain.
 
 

Angular shear is a parameter that allows us to quantify the amount of internal rotational deformation. The parameter [[psi]] (psi) is referred to as the angular shear and describes the changes in the orientation of lines.
 
 

Permanent shearing is analogous to displacing a deck of cards. Youwill not always see shearing produced by slipping between bedding planes. Sometimes youwill be ablw to observe it only throughdeformed markers such as fossils:

 Inser figure

 Do lines keep their original length? Yes, if parallel to the shearing direction.

 Does the direction of maximum and minimum extensionwhith the ellipse change with the amount of deformation? Yes.

If we use a circle as amarker and examine the shearing we see that the circle becomes an ellipse. The ellipse is a good geometric tool with whichtoexamine the defree and type of deformation.