Testing models – Structural restoration. Ben Peach’s field notebook: 1880s. Line-length balancing Area balancing

Is the cross-section correct? Wrong question! Cross-section – a 2D representation of a model Is the style appropriate? Is the cross-section consistent with the style? Is the cross-section physically plausible?

Section balancing Testing structural interpretations graphically

Consider fault-bend folds

Pin line Trail line All layers must experience the same horizontal shortening Assume plane strain. If NO DISTORTIONAL STRAIN – then bed-length is conserved – Line-length balancing.

A’ = Area above regional A = area “lost” D t A’ = A = (displacement) x (depth to detachment) = Dt AREA BALANCE

D t A’ = A = (displacement) x (depth to detachment) = Dt Assumes we can measure displacement – so needs a “key bed” that retains bed-length

Mitra 2003 J Struct Geol

More to follow…..