Abstract -
Faults commonly consist of arrays of en echelon segments. Displacement is transferred between a pair of adjacent segments by deformation of the intervening rock volume, or relay zone. In normal faults this deformation gives rise to bed rotations to form a relay ramp between segments. In most current models of relay zone evolution describe a progression of structure from an intact relay ramp, with ramp rotation increasing as displacement increases, through to the formation of a through-going fault when the relay ramp is bypassed, or breached, by the formation of a fault linking the initial segments. This evolution has been proposed from extensive studies of relay geometries at different displacements and is supported by the relatively much fewer studies of relay zone kinematics.
We present the results of detailed kinematic analyses carried out using displacement backstripping on a segmented fault array from South East Asia which demonstrate a more complex 3D evolution of segment boundaries than this simple model suggests. Our analyses show, not only that a relay ramp may be breached at one structural level and simultaneously intact at another, but also that ramp rotation can continue after the formation of a through-going fault. The data also show that an initial through-going fault bend can, with increasing displacement, develop a splay and a related intervening 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 be reached by an alternative mechanism i.e. the ‘ramp’ and splay forms after a fault bend is established.
Abstract of talk given to:
Tectonic Studies Group Annual Meeting, Edinburgh, January 2012.