Geological prior information and its applications to geoscientific

Geological information can be used to solve many practical and theoretical problems, both within and outside of the discipline of geology. These include analysis of ground stability, predicting subsurface water or hydrocarbon reserves, assessment of risk due to natural hazards, and many others. In many cases, geological information is provided as an a priori component of the solution (i.e. information that existed before the solution was formed and which is incorporated into the solution). Such information is termed 'geological prior information'. The key to the successful solution of such problems is to use only reliable geological information. In turn this requires that: (1) multiple geological experts are consulted and any conflicting views reconciled, (2) all prior information includes measures of confidence or uncertainty (without which its reliability and worth is unknown), and (3) as much information as possible is quantitative, and qualitative information or assumptions are clearly defined so that uncertainty or risk in the final result can be evaluated. This paper discusses each of these components and proposes a probabilistic framework for the use and understanding of prior information. We demonstrate the methodology implicit within this framework with an example: this shows how prior information about typical stacking patterns of sedimentary sequences allows aspects of 2-D platform architecture to be derived from 1-D geological data alone, such as that obtained from an outcrop section or vertical well. This example establishes how the extraction of quantitative, multi-dimensional, geological interpretations is possible using lower dimensional data. The final probabilistic description of the multi-dimensional architecture could then be used as prior information sequentially for a subsequent problem using exactly the same method. For decades, specific geological informat ion has been transferred to other domains, helping solve applied and theoretical problems. These include, for example: 9 Informat ion about typical geological architectures in a particular envi ronment allows subsurface properties to be estimated away from drilled observation wells in order to assess hydrocarbon or water reservoir potential (e.g. Mukerj et al. 2001; Schon 2004). 9 Assessments of predicted geohazard risks contributes to the pricing of life and property insurance (e.g. Rosenbaum & Culshaw 2003). 9 The distr ibution of ancient reef corals, combined with the relationship between coral growth and sea level, allows prediction of both past sea level oscillations and how future sea level change might affect the distribution of modern reefs (e.g. Potts 1984; B u d d e t al. 1998). Historical knowledge of slope stability in different geological environments allows proposed building projects to include appropriate remedial action against such risks (e.g.