9.) (Still referring to figure 2.) If you found evidence that this rock was deformed by pure shear only rather than by simple shear, what is the minimum number of deformation events required to produced the observed strain? Please explain using the strain ellipse. (5 points)

Pure shear is a coaxial deformation. During coaxial deformation the principal stretch directions of the strain ellipse do not rotate. Therefore lines that parallel directions of shortening will always shorten, lines that parallel directions of extension will always extend during the same progressive coaxial deformation event. In order to have shortening followed by extension, as was the case for the small quartz vien, and invoke only pure shear coaxial deformation would require two deformation events for which the orientation of the stress field are significantly different. Thus, the strain ellipses associated with each deformation event would be significantly different with respect to orientation of S1 and S3 on the outcrop. In this way you shorten an object (fold it) during the first deformational event  (parallels S3 ), then extend it (pull it apart into boudins) during the second deformation event (parallels S1).
 


10.) On figure 3 draw and label sN , sS , and determine the angle q. (5 points)

The angle q is the acute angle between the plane of interest and the stress vector.

11.) Calculate the magnitude of sN and sS. (5 points)

The angle q = 60°;
sN= s * sinq = 100 MPa  * (.866) = 86.6 MPa.
sS= s * cosq = 100 MPa  * (.5) = 50 MPa.