If there is strong lateral heterogeneity in the near-surface only, layer stripping works well. If there is complexity at all depths, all model parameters should be determined simultaneously after careful construction of a starting model that allows the appropriate rays to be traced to all pick locations. Model assessment establishes the reliability of the final model. Direct model assessment techniques that derive alternative models that satisfactorily fit the real data are the best means for establishing the absolute bounds on model parameters and whether a particular model feature is required by the data. Examples of the types of ray groups considered for wide-angle traveltime modelling.
Solid lines are raypaths and dashed lines are layer boundaries.
Dotted lines indicate S-wave segments for converted raypaths. For each step, an example of the rays for one shot is shown above the corresponding traveltime curves for all phases with the phases of interest labelled and indicated by a thicker line. Circles and open squares indicate velocity and depth nodes, respectively. Note that the layers being solved for start out laterally homogeneous in each step. Structural classification of model types.