Testing models –Structural restoration.

Ben Peach’s field notebook: 1880s.

Line-length balancingArea 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 shorteningAssume 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…..