Inverse Methods, Resolution and Implications for the Interpretation of
Lithospheric Structure in Geophysical Inversions
Abstract
Inverse methods form the basis of many investigations of the structure
of the lithosphere-asthenosphere system as they provide the basis for
physics-based subsurface imaging from surface and/or near-surface
measurements. Steady increases in computational capabilities and
methodological improvements have resulted in increasingly detailed
three-dimensional models of the Earth based on inverse methods. While
these models can show an impressive array of features, it may be
difficult for non-specialists to assess which aspects can be considered
reliable and which are tenuous, or are artefacts of the mathematical
formulation or data collection. In this paper we address the fundamental
issues of feature reliability due to limited resolution and model
sensitivity to data noise for researchers who do not work with
intimately with inverse methods. We include and introductory overview of
the mathematical formulation of inversion methods and define commonly
used terms and concepts. We then present two case studies based on data
from USArray in the western United States. The first case study utilizes
magnetotelluric array data to construct a three-dimensional model of
electrical resistivity to a depth of approximately 300 km. We use this
example to demonstrate fundamental issues regarding data fit, data
coverage, and model parameterization. The second case study discusses
how we can incorporate petrological and mineral physics information
directly into the inversion approach to create models that are
compatible with constraints on the temperature and composition of the
lithosphere. We will discuss the implications for practical use of these
models in interpretations and provide guidelines on how to evaluate such
models.