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Wytch Farm field, UK. The lower Cretaceous breakup unconformity at about one third from the top. Faulting is largely related to the breakup. The crossing faults in the middle are correctly handled. Data courtesy BP.

UK, Wytch Farm: faulting and unconformity related to the break-up of the Atlantic

Wytch Farm seismic section, geology, unconformityWytch Farnm unfaulting, unconformity, strainWytch Farm unfaulted without honouring the unconformity. Strain.Wytch Farm unfaulted without honouring the unconformity causing excessive strainWytch Farm unfaulted honouring the unconformity. Good.

Notes: excessive strain will occur in unfaulting when the unconformity is ‘missed’, see images below. Strain is generally a good warning that something is wrong.

1. Original interpretation

Note the unconformity (purple, top) and the correlation of the first horizon (Cornbrash, yellow). Across the main fault the yellow horizon on the left side seems to continue as a strong uncoloured event on the right side.

2. Unfaulted without honouring the unconformity

The interval between the unconformity (purple, top) and the first horizon (Cornbrash; yellow) is heavily compressed on the right side of the main fault.

3. Unfaulted without honouring the unconformity

Strain display, colour scale 10% compression (light purple), 20% compression (dark purple).

Large strain patches because the seismic between the yellow and blue horizons needs to be compressed on the hanging-wall side of the main fault to correlate across the fault.

3. Unfaulted honouring the unconformity

No strain. Perfect thickness and seismic character correlation across the main fault.