MODELING OF STRUCTURAL COMPLEXITY IN SEDIMENTARY BASINS - THE ROLE OFPREEXISTING FAULTS IN THRUST TECTONICS

Analogue and numerical models have been used to study the role of pre- existing faults in compressive regimes. From a theoretical point of vi ew, reactivation is mainly controlled by fault attitude, stress regime and frictional properties of fault planes. In scaled-down sandbox exp eriments, precut faults are introduced in the homogeneous granular med ia with a nylon wire which is forced through the sand cake producing a thin planar disturbed zone. Systematic experiments of thrust inversio n with various dips and strikes of such planar discontinuities have be en modelled. Comparison of experimental results with theoretical diagr ams indicate that disturbed zones have a friction angle which is 10-20 % lower than the homogeneous sand and that the compressive regime in t he sandbox has a shape factor close to 0.4. The static analysis of fau lt reactivation is in accordance with the experimental observations ex cept for pre-existing faults dipping at very low angle. However, numer ical modelling using the Udec code shows that low-angle faults can be reactivated as a result of stress concentration in the lower part of t he fault. In addition, sandbox experiments indicate that in thrust sys tems, reactivation of pre-existing faults is not only dependent on the ir attitude but also on their spacing and location relative to the thr ust system.