The Inversion of Deep Seismic Soundings: Problems and Constraints
Some examples of record-sections obtained in the exploration of the Crustal Structure in Italy (Italian Geodynamics Project) are shown, describing the main features of the recorded events.
On the base of both kinematic and dynamic considerations the conclusion is drawn that the recorded events should represent the effect on surface of “diving waves” that are generated if a continuous variation of velocity with depth is verified.
Some approximate formulas for calculating the velocity-depth function are given, as well as the principles and recurrence formulas for calculating the travel-time curves from a crustal model (direct problem) and the crustal model from the obtained travel-time curves (inverse problem) in the case of horizontal layering.
Ambiguities arise in calculating the “low-velocity layers”, but these ambiguities do not affect so much the interpretation of layers in the lower crust.
The principles of the “ray tracing method” are explained, which should be applied for a better refining of the crustal model along a profile where lateral inhomogeneities are present. Some examples of application illustrate this concept.
At the end some representative cross-sections are shown and a general description of the crustal structure in Italy is given, pointing out the large variations of typology evidenced in the different regions and the consequent geodynamic implications.
KeywordsLower Crust Crustal Structure Direct Problem Recorded Event Crustal Model
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