Deduction of earth strains from survey data

Abstract

In deducing earth strains from repeated triangulation surveys, it is advantageous to extract the shear components of strain $γ1=(∈11−∈22)andγ2=(∈12+∈21)$ separately. Unlike the dilation and rotation components of strain, $12(∈11+∈22)and12(∈12-∈21)$⁠, these shear components can be determined locally, each triangle giving one measurement for γ₁ and γ₂, without requiring knowledge from adjoining areas. It follows that it should be possible to extract much more and better information about the shear strains from existing survey data than has been extracted hitherto.