DEM: Normal faulting 1. The effect of syn-kinematic sedimentation on faulting in pre- and syn-kinematic layers

An understanding of the interaction between sedimentation and fault displacement and resulting stratigraphy is key to improve interpretation of seismic data. A modification of one parameter such as sedimentation impacts fault propagation in the syn-tectonic stratigraphy and, as a result, local accommodation space and subsequent deposition locations creating variation in overburden thickness which then affects faulting in the pre- and syn-tectonic layers. A complicated feedback loop (chicken and egg situation) that is sometimes hard to unravel. Here, the relationship between changes in sedimentation and the resulting stratigraphy and faults in both pre- and syn-tectonic sedimentation during basement fault propagation is shown. This is investigated in relation to a pair of domino faults with constant displacement. Initially, the fault planes dip at 50^o which rotate to 33^o at the end of an experiment.

The modelling is carried out using the discrete element method where the methodology and experiment set-up are described in file NF.intro.pdf. These pages and movies show results from 7 experiments where sedimentation is varied. All other parameters (for example: fault displacement, the mechanical properties of elements, timing of sediment addition) are constant.

Experiments run to 3,000,000 timesteps and sediment is input 25 times (every 120,000 timesteps), divided into 5 intervals. Data is output every 40,000 timesteps (75 files) to generate the movies. Sediment is added to a defined elevation which changes in model units at the start of an interval or remains fixed. The models shown have sediment deposited at a level that is:

• constant (0.0, 0.25 and 0.50 unit)
• • Experiments: constant_0.0, constant_0.25, constant_0.5
• rising (0.0 to 1.0 units) or falling (1.0 to 0.0 unit)
• • Experiments: rising and falling
• rising to interval 3 (0.0, 0.5, 1.0 unit) and then falling in intervals 4 and 5 (0.5, 0.0 unit)
• • Experiment: rise.fall
• falling to interval 3 (1.0, 0.5, 0.0 unit) and then rising in intervals 4 and 5 (0.5, 1.0 unit)
• • Experiment: fall.rise
• alternating at intermittently high and low amounts starting in interval 1 with either 0.0 or 1.0 unit increase in deposit height
• • Experiments: interval_0.1 and interval_1.0

The intention of this data is not to provide full interpretation and discussion of the results but to provide an indication of the complexity within observed stratigraphy when only sedimentation changes. When presented with only a static representation of stratigraphy it is sometimes tricky to understand what is observed, hopefully these movies and images will help in some way.