One of the most important tasks of the seismic tomographer is to make sure he or she knows the limitations of the final model, and is able to convey that knowledge to others in a digestible form. This is not an easy problem: even within a narrow band of acceptable χ2 values, there will be infinitely many models that satisfy the data at this misfit level. Yet some features will change little among those models. Such features are ‘resolved’ if the change is less than some pre-specified variance. Of course, one cannot calculate infinitely many models and usually resigns oneself to present one possible inversion outcome with an assessment of its resolution and uncertainty.

To estimate resolution and uncertainty is a major task that will usually consume far more time than the actual inversion. As we shall see, all of the methods we currently know have shortcomings. Our means to present the results in an accessible form are equally poorly developed. There exists also some confusion about the meaning of damping parameters and their role in resolution and sensitivity tests. Many tomographers do not distinguish clearly between Bayesian constraints (damping parameters based on somewhat objective information) and damping parameters used to obtain a smooth model, which are inherently subjective if not based on prior information.