Tectonic strain ratios on a surface passing through the centre of a deformed, pod-shaped lava pillow are close to the ratio of the maximum/minimum selvage thicknesses. This approximation is valid for a variety of cases with an accuracy of 20% even where the section does not pass through the centre of the pillow but as long as the section passes through the central third of the pillow. Variation in selvage thickness is unlikely to provide a meaningful estimate of strain where the pillow shape was originally tubular.

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