
Strain analysis – Wellman method:

Example: The figure below shows the hinge and median lines of eight deformed brachiopods.

Use line AB and determine the strain ellipse.
Procedure :
1.
Draw line AB, and two or three more lines parallel to line AB onto the tracing paper.
2.
Overlay point A (on the tracing paper) on the intersection point of the hinge and median line of fossil 1. Make sure line AB (and other parallel lines) on the tracing paper remain parallel to line AB on the image at all times.
3.
Trace (in faint lines, so you erase them) the hinge line and median lines of brachiopod 1 through point A. Draw these about 5 cm.
4.
Overlay point B on the intersection point of the hinge and median line of fossil 1. Make sure line AB
(and other parallel lines) on the tracing paper remain parallel to line AB on the image at all times.
5.
Trace (in faint lines, so you erase them) the hinge line and median lines of brachiopod 1 through point B. Draw these about 5 cm or long enough to intersection the lines through point A.
6.
Find the two intersection points of the parallelogram. Mark them with the fossil number (e.g., 1).
7.
Repeat steps 2 through 6 for all other fossils.
8.
Draw a best fit ellipse through the points of intersections.
9.
Find the long and short semi-axes of the strain ellipse.
10.
Determine the strain ellipse (Rs).
See solution below! Rs
≃
1.49