Strain and Shear Calculator

StrainCalculator©

Recalculates strain and shear parameters from any subset of strain data and presents the results graphically and numerically. These tools have been developed principally as a teaching aid, although I find the shear zone graphics a very useful way to estimate displacement in some natural shear zones (see example below)
Free

What it does

  • StrainCalculator presents strain data and calculations graphically and numerically. Conversions of strain ratios to stretches at a given volume change can be plotted directly onto a logarithmic strain plot.
  • The shear calculator allows all other parameters to be calculated for any plane strain shear characterized by any one parameter (shear strain, displacement, ellipticity, deformed and undeformed orientations of strain axes, or of arbitrary lines, etc.). These can be calculated for the entire spectrum of plane strain shears from simple shear, through general shear, to pure shear. 
  • The shear calculator is particularly useful for obtaining rough estimates of displacement of shear zones of known width and only moderate shear strain. The example below shows the protomylonitic fabric in core within a gold-bearing shear zone (in the Democratic Republic of the Congo). The 25m-wide horizontal shear zone had been interpreted to be at the base of a nappe of kms-scale displacement. A quick plot of the observations in StrainCalculator show that this cannot be true. The grain fabric has an approximate ~10:1 aspect ratio (R), and the grain fabric is oriented at about 17 degrees to the shear zone itself. Entering either of these values into StrainCalculator shows that such a shear is produced by a displacement of 2.85 times the width of the shear zone. That is, the displacement required to produce the observed fabrics is only about 70 metres. (Given that we have two separate strain parameters the calculator also shows that it is a Simple Shear shear zone.
Strain_Calculator_zip.zip
Zip file (.zip) containing the full set of installation files [~5.2 Mb]

Notes
  • The software is specific to Microsoft Windows. (It may install and run under Windows emulations on Macs, although Help links within each application will not work).