How we deal with our faults

On July 4th 2019 partners of the GeoERA projects HIKE and GeoConnect3d met in Utrecht at TNO-Geological Survey for a joined workshop where they discussed “how to deal with faults”. Whereas the main mission of HIKE is to develop a European Fault Database (FDB), GeoConnect3d faces the challenge of implementing their Structural Framework methodology (SF).

Dealing with our faults at the joint HIKE-GeoConnect³d workshop at TNO.

HIKE’s FDB envisions to store a comprehensive set of faults including their static and dynamic geological and physical characteristics that can be utilized for the assessment of seismic hazards, ground movements, leakage and fluid migration, sealing capacities, fluid flow and other types of fault behavior.

GeoConnect³d aims to provide to stakeholders a coherent geological context for evaluating subsurface applications and resolving subsurface management issues and the SF is the method to achieve this. The SF proposes to be the dominant, superseding model, in which geological maps and models would become the details. But what will the SF be? The definition of the SF slowly crystalized in the past months as was nicely described in four previous blogs by Kris Piessens and Renata Barros. To cut a long story short, the SF is about geological units and their limits and serves as the medium to communicate geomanifestations (i.e., distinct local expression of geological processes, past or ongoing). The SF is defined by limits, which can obviously be faults, whereas intervening terranes represent the geological units that are being defined by the faults. The goal of a structural framework is to structure things, to tie them together. This tying together needs a way to relate the structures and obviously this is achieved in an information system where both hierarchy, semantic relations and vocabulary are standardized.

It thus appears that both projects rely on structures and it happens that both projects chose the Dutch-Belgian part of the Roer Valley Graben as pilot area for testing the FDB and the SF. Not surprisingly, a workshop followed to discuss preliminary results. For the HIKE FDB the challenge was to connect and harmonize Dutch and Belgian datasets across the border. Previously, connecting cross-border datasets was done on the Geological level while now the focus has shifted to the conceptual level. As geologists tend to stick to their own truth, discussions on the geological level involved convincement, discussion, arguments and sometimes even fights. However, with a fault vocabulary and-hierarchical concept at hand, cross-border discussions on fault harmonization suddenly focus on implementing a common and workable classification and ranking system.

The cross-project aspect of this workshop was how GeoConnect³d’s Structural Framework could benefit from HIKE’s Fault database by adopting and synchronizing both fault hierarchy level and the vocabulary at the fault attribute level. Hereby we focused on building a hierarchy which is practical for the FDB partners’ practice, but still usable for constructing the Structural Framework. The latter mainly focused on how to bring the timing aspect to use. A workable and well-elaborated use case for the Belgian part of the area was presented by VITO. TNO presented their approach to ranking faults in the Dutch part. Realizing that faults can be dynamic and evolving structures through time, future challenges will be to combine the temporal and hierarchical fault aspects as well the scale range at which fault can be visualized.

Mind you that this is work in progress. We hit common ground and we really feel we are making good progress in aligning things, but we also realize there still is much work to do

Johan ten Veen and Harry Middelburg
TNO – Geological Survey of the Netherlands

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