A new model for the structural development of extensional basins is outlined. The model suggests a close similarity in geometry between faults in high extension basins such as the North Sea and those in contractional zones. The geometric analogues are discussed and where necessary new terms are introduced to describe the structural style in the context of basin formation. Parallels are noted between contractional and extensional systems in deep crustal control on ramp and flat deformation zones which are now being interpreted from deep reflection work, e.g. MOIST and COCORP. The model is based on interpretation of industry seismic records particularly in the North Sea, and on field analogues of extensional faulting in the Basin and Range province of Nevada.

Interpretations of seismic images are used to analyze subsurface geology and form the basis for many exploration and extraction decisions, but the uncertainty that arises from human bias in seismic data interpretation has not previously been quantified. All geological data sets are spatially limited and have limited resolution. Geoscientists who interpret such data sets must, therefore, rely upon their previous experience and apply a limited set of geological concepts. We have documented the range of interpretations to a single data set, and in doing so have quantified the "conceptual uncertainty" inherent in seismic interpretation. In this experiment, 412 interpretations of a synthetic seismic image were analyzed. Only 21% of the participants interpreted the "correct" tectonic setting of the original model, and only 23% highlighted the three main fault strands in the image. These results illustrate that conceptual uncertainty exists, which in turn explains the large range of interpretations that can result from a single data set. We consider the role of prior knowledge in biasing individuals in their interpretation of the synthetic seismic section, and our results demonstrate that conceptual uncertainty has a critical influence on resource exploration and other areas of geoscience. Practices should be developed to minimize the effects of conceptual uncertainty, and it should be accounted for in risk analysis.

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