Abstract
Abstract. The quantitative integration of geophysical measurements with data and information from other disciplines is becoming increasingly important in answering the challenges of undercover imaging and of the modelling of complex areas. We propose a review of the different techniques for the utilisation of structural, petrophysical, and geological information in single physics and joint inversion as implemented in the Tomofast-x open-source inversion platform. We detail the range of constraints that can be applied to the inversion of potential field data. The inversion examples we show illustrate a selection of scenarios using a realistic synthetic data set inspired by real-world geological measurements and petrophysical data from the Hamersley region (Western Australia). Using Tomofast-x's flexibility, we investigate inversions combining the utilisation of petrophysical, structural, and/or geological constraints while illustrating the utilisation of the L-curve principle to determine regularisation weights. Our results suggest that the utilisation of geological information to derive disjoint interval bound constraints is the most effective method to recover the true model. It is followed by model smoothness and smallness conditioned by geological uncertainty and cross-gradient minimisation.
Highlights
Geophysical data provide detailed information about the structure and composition of the Earth’s interior otherwise not accessible by direct observation methods, and these data play a central role in every major Earth imaging initiative
Note that the application of the ADMM bound constraints can be interpreted as being analogous to clustering constraints where the following conditions are met: 1. the centre values depend on both the current model m at any given integration and petrophysical information defining a and b; 2. the weight assigned to each centre value changes from one iteration to the as a function of the distance between mk and the closest bound, and the number of iterations mk has remained outside Bk
Tomofast-x was developed with the intent of providing practitioners with an inversion platform accounting for various forms of prior information and geophysical data sets
Summary
Geophysical data provide detailed information about the structure and composition of the Earth’s interior otherwise not accessible by direct observation methods, and these data play a central role in every major Earth imaging initiative. Effective inversion of potential field data necessitates the utilisation of constraints derived from prior information extracted from geological and petrophysical measurements or other geophysical techniques whenever available. When limited geological information is available, the assumption is that spatial variation of density and magnetic susceptibility are colocated This can be enforced through simple structural constraints encouraging structural correlation between the two models using Gramian constraints (Zhdanov et al, 2012) or the cross-gradient technique introduced in Gallardo and Meju (2003). We present a versatile inversion platform designed to integrate geological and petrophysical constraints to the inversion of gravity and magnetic data at different scales. We perform single physics inversion of gravity data and study the influence of prior information using several amounts and types of constraints, and run joint inversion of gravity and magnetic data. We place Tomofast-x in the general context of research in geophysical inverse modelling and conclude this article
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