Interrogating the volume of the East Irish Sea sedimentary basins using probabilistic tomographic results

The ultimate goal of a scientific investigation is usually to find answers to specific questions: what is the size of a subsurface body? Does a hypothesised subsurface feature exist? Which competing model is most consistent with observations? The answers to these and many other questions are low-dimensional, yet must often be inferred from high-dimensional models and data. To address the questions, existing information is reviewed, an experiment is designed and performed to acquire new data, and the most likely answer is estimated. Typically the answer is interpreted from geological and geophysical data or models, but is biased because only one particular forward function (model-data relationship) is considered, one inversion method is applied, and because human interpretation is a biased process. Interrogation theory provides a systematic way to answer specific questions using statistically unbiased estimators. It combines forward, design, inverse and decision theory, and focuses them to maximise information on the space of possible answers.

This study estimates the volume of the East Irish Sea sedimentary basins in the UK using 3D shear wave speed models derived from surface wave dispersion inversions. In order to answer volume-related questions, it is first necessary to define a target function that translates any (high-dimensional) model into (1-dimensional) volumes of interest. A key revelation of this study is that while the majority of computation may be spent solving inverse problems probabilistically, much of the skill and human effort involved in answering real-world questions may be spent defining and calculating those target function values in a clear and unbiased manner.