Quadshear - A New Kinematic Model for Clay Smear Development

SUMMARY A new kinematic model, based on the Trishear model, has been developed to simulate fault-propagation folding in ductile, clay-rich strata between two propagating faults, a process which often leads to the development of clay smears which can cause the fault to seal. The new model is used to determine the amount fault throw required for the continuous clay smears to break down, normalised to the bed thickness (this ratio is often known as the critical clay smear factor or CCSF). We find that the maximum length of continuous clay smear is primarily dependent on the position of the clay-rich bed in the stratigraphy, and the rate of propagation of the faults. The thickness of the clay-rich bed, the horizontal offset of the two propagating faults and the width of the fault-propagation folds have much less impact on the maximum length of continuous clay smear.