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Joint inversion of gravity and magnetic data under lithologic constraints

Departamento de Física Aplicada, Universidad Central de Venezuela, Caracas

John McGaughey

Mira Geoscience Ltd., Montreal, Quebec, Canada

Corresponding author: bosch@esc.cam.ac.uk; mbosch@reacciun.ve

The first 20% of the full text of this article appears below.

Interpreting exploration data requires combining different types of information to solve the geologic puzzle. It implies bringing together all data components into an image that makes conceptual sense in terms of the geology of the exploration area. The identification of geologic objects and the inference of a spatial description of the lithology—consistent with all available information—are the objectives of the process.

The more information utilized, the more certain is the result of the inference. The interpretational process should serve to combine different types of geophysical data, petrophysical information on the rock properties, and information on the geology of the area. It is an interdisciplinary process, performed by an expert or a multidisciplinary team, the desired outcome being a common earth model, or class of models, known to satisfy both the conceptual geologic understanding and all available geoscientific data.

The object of the present work is to incorporate geophysical inversion methodologies as a tool in geologic interpretation, describing a process to jointly invert gravity and magnetic data that takes into account petrophysical and geologic constraints. Basically, the method seeks lithologic models that explain the overall data, helping with the task of quantitatively reconciling the available geologic and geophysical information. The process uses a geostatistical model to couple the lithology with realistic density and magnetic susceptibilities. Hence the values of density and magnetic susceptibilities are a priori conditioned by the lithology, avoiding unrealistic excursions allowed by common inversion approaches. On the other hand, prior information about the lithology, such as a geologic surface map or an interpreted drill hole, is incorporated in the inversion and satisfied by the resulting models.

	Joint model and multiple data sets

 
The first difference with common inversion approaches is that here we describe the media with a joint model—i.e., a model that simultaneously describes lithology, density, and magnetic susceptibility. The major lithologic categories . . . [Full Text of this Article]