Abstract -
Faults commonly consist of arrays of en echelon segments. Displacement is transferred between adjacent segments by rotation of the intervening rock volume to form a relay ramp. Current models describe a progression of structure from an intact relay ramp to formation of a through-going fault when the relay ramp fails as displacement increases. This evolution has been proposed from extensive studies of relay geometries and is supported by much fewer studies of relay zone kinematics.
We present a detailed kinematic analysis of a segmented fault array from South East Asia which demonstrates a more complex evolution of segment boundaries than the conventional model suggests. Our analysis shows that a relay ramp may be breached at one structural level and simultaneously intact at another. The data also show that an initial through-going fault bend can develop a splay and a related zone of high strain. This geometry arises when a relay bounding fault propagates to structural levels at which a fault bend has already been established. In this case fault and bed geometries very similar to that of a breached relay ramp can result from an alternative mechanism i.e. the 'ramp' and splay forms after a fault bend is established.
Abstract of talk given to:
Irish Geological Research Meeting, University College Cork, February 2012.