Abstract: Close to the Earth's surface or in regions of high overpressure, cohesive rocks fail in extension, and normal faults in these rocks are commonly dilatant. The transition in failure mode from tensile to shear is another part of dilatant faults where structural style and fault zone architecture is not well studied, especially in 3D. This makes ground-water and hydrocarbon flow predictions notoriously difficult, although the two modes of faulting are common in carbonates with large variance in mechanical properties and brittleness indices.
A high resolution method to study these structures is in physical scale models, using a cohesive powder. By varying the overburden stress, failure mode can be varied from tensile over hybrid to shear. Hardening and excavating the cohesive layer, in combination with 4D modelling in using CT-scans allows investigation of 3D structures at very high resolution. There are two end member structural domains that differ strongly in their attributes: in the tensile domain strongly dilatant faults with steep open fissures, vertical faults and large sharp changes in strike at segment boundaries and branches; in contrast to the shear domain with shallower fault dips, fault plane striations, undulating fault traces and smaller changes in strike at branches. These attributes could be seen in seismic and provide a way to better predict fault zone structure in the subsurface.
These models present a tantalizing look into the evolution of internal structure of dilatant fault zones in carbonates, and show a range of processes such as extensive fragmentation processes, vertical, gravity-driven transport of breccia along the fault zones, and the formation of small caves in dilatant jogs. The general effect of a mechanical stratigraphy, even if strength contrast is small, is to make the fault zones wider, creating more complex structures and associated layer-parallel shear.
Field examples of many of these structures can be found in excellent outcrops in North Oman: I will illustrate the concepts
Bio: I lead an institute at RWTH Aachen University with academic and technical staff, BSc , MSc and PhD students, and a large externally funded research program. From 2006 to 2012 I was Inaugural Dean of the Faculty of Science of the newly established German University of Technology in Muscat, Oman, and set up and organized the Department including the hiring of staff and establishing a BSc and MSc programme, in a complex and multicultural environment.
Over my career at Shell Research and Academia, I have worked in interdisciplinary projects on problems related to the interaction of GeoFluids and rock deformation, at a wide range of scales, using field studies, laboratory measurements, analogue modeling and numerical simulation. I have built a network of cooperations and contacts in both academia and industry and have a long record of externally funded projects sponsored by National Science Foundations, European Research Funding, Oil Companies, Nuclear Waste Management agencies and the Solution Mining industry. Key interests of our research are top seals and fault seals, fractures and fracture sealing, multiscale microscopy of nano-to microporosity, tectonics of the Oman Mountains, and the develoment of state of the art geoscience teaching in the Middle east.
Many of our graduates started successful careers with our sponsors, and we started a company (m-a-p.expert) specialised in complex multiscale imaging of fluid- mineral relationships in reservoirs.
I enjoy initiating interdisciplinary research projects in basic and applied Geoscience, building an institute, design innovative instruments, teaching Geoscience at all levels, coaching young talent in intercultural environments and presenting geoscience issues with societal relevance to the public.