http://www.sci.sdsu.edu/visualstructure/vsg/visualstress_html/chapter6_4.htm
http://www.geosci.usyd.edu.au/users/prey/Teaching/Geos-2123/Strain/Sld42.html
https://opentextbc.ca/geology/chapter/12-1-stress-and-strain/
http://geologylearn.blogspot.com/2017/01/why-perform-strain-analysis.html
http://tech.25.physiolive.de/block-diagram-geology.html