Roberts, D.T. (Cardiff University) | Crook, A.J.L. (Three Cliffs Geomechanical Analysis) | Cartwright, J.A. (University of Oxford) | Profit, M.L. (Rockfield Software Limited,) | Rance, J.M. (Rockfield Software Limited,)
Polygonal Fault Systems (PFS) are increasingly observed in seismic data of the subsurface. These unusual networks of normal faults are known to develop over vast areas in fine-grained sequences which in many cases may form the regional caprock. Consequently, there is the potential for PFS to compromise the integrity of these sequences with obvious implications for subsurface fluid migration. The processes leading to the formation of PFS remain poorly understood, although their confinement to particular sediment packages and spatial extent are powerful arguments for a constitutive control. The work presented here attempts to progress recent efforts examining a diagenetic trigger for polygonal fault genesis. More specifically, investigations of diagenetically sourced structure development in mudstones have been undertaken in order to formulate a geomechanical argument to explain their formation. This argument is tested in finite strain computational models using the geomechanical code ELFEN, so that the formation over geological time can be studied. Prediction of PFS in both two and three dimensions are presented that demonstrate that this modelling approach can predict realistic PFS geometries including the observed transition from random to preferential fault alignment with increasing degree of stress anisotropy.
A comprehensive understanding of rockfall trajectories is the key to effectively control rockfall hazards. An important characteristic that distinguishes different rockfall models is the presentation of the rock block in the model. Lumped mass models represent rock as a dimensionless point while rigid body models can consider block geometry in rockfall simulations. The potential blocks of the Mardin Castle are selected to study the differences between the lumped mass and the rigid body simulations. The trajectories of the lumped mass model are exactly the same for any size of blocks while rigid body models generate different rockfall paths and bounce height and run out distance accordingly. Increase in block size and non-circularity, cause large divergence between lumped mass and rigid body models. More reliable and conservative protection measures can be designed according to the rigid body simulations.