The easiest way is to run a slope stability analysis using available software (such as PCStable, XStable, Slope/W, etc). In the analysis, you have to allow a second layer where the fault is approximately located. Clay in the fault layer shall be assigned with remolded strength, which is lower than the peak strength. Make an imaginary layer as practical for the analyses... say 0.5m thick zone, or even 1 m thick. In the analyses, you can forced the slope failure to go along the fault line, or during itineration, usually it will choose along the weak soil layer, ie the critical slope failure will pass through the weak layer. Note that direction of the clay fault is importance with respect to the slope of the cliff. Because the coralline layer can be assumed to have higher friction angle than the clay... it will be a deepfailure. Effective stress analysis will be required for long term stability... therefore no or little cohesion is allowed for the clay.
Hope that this help you along !
