In deducing earth strains from repeated triangulation surveys, it is advantageous to extract the shear components of strain γ1=(1122)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.

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