An elastic map \(\mathbf{T}\) associates stress with strain in some material. A symmetry of \(\mathbf{T}\) is a rotation of the material that leaves \(\mathbf{T}\) unchanged, and the symmetry group of \(\mathbf{T}\) consists of all such rotations. The symmetry class of \(\mathbf{T}\) describes the symmetry group but without the orientation information. With an eye toward geophysical applications, Browaeys & Chevrot developed a theory which, for any elastic map \(\mathbf{T}\) and for each of six symmetry classes \(\Sigma \), computes the “\(\Sigma \)-percentage” of \(\mathbf{T}\). The theory also finds a “hexagonal approximation”—an approximation to \(\mathbf{T}\) whose symmetry class is at least transverse isotropic. We reexamine their theory and recommend that the \(\Sigma \)-percentages be abandoned. We also recommend that the hexagonal approximations to \(\mathbf{T}\) be replaced with the closest transverse isotropic maps to \(\mathbf{T}\).

弹性图\(\mathbf{T}\)将某些材料中的应力与应变相关联。\(\mathbf{T}\)的对称性是使\(\mathbf{T}\)保持不变的材料的旋转，并且\(\mathbf{T}\)的对称群由所有此类旋转组成。\(\mathbf{T}\)的对称类描述了对称群，但没有方向信息。着眼于地球物理应用，Browaeys 和 Chevrot 开发了一种理论，对于任何弹性图\(\mathbf{T}\)和六个对称类\(\Sigma \)中的每一个，计算“ \(\Sigma \ ) - \(\mathbf{T}\)的百分比”  。该理论还发现了一个“六边形近似”——对\(\mathbf{T}\)的近似，其对称性类至少是横观各向同性。我们重新审视他们的理论并建议放弃\(\Sigma \)百分比。我们还建议将\(\mathbf{T}\)的六边形近似替换为最接近 \(\mathbf{T}\) 的横向各向同性图。