S U M M A R YAn inversion scheme that determines a velocity model simultaneously from normalincidence reflection and refraction/wide-angle reflection seismic data has been developed, tested, and applied to real seismic data. Simultaneous inversion minimizes the non-uniqueness of inversion results. A common midpoint (CMP) stacked reflection section provides a detailed image of the structural configuration in time. Refraction or wide-angle reflection data can be used to derive a velocity model. If both refraction data and normal-incidence reflection data are available along coincident profiles, simultaneous inversion of the data sets can produce an improved model. With the extra control of the interface depth provided by reflection data, it is also possible to avoid ambiguity of phase identification. The commonly used damped-least-squares (DLS) inversion method often results in significant inversion artefacts. We provide effective methods for reducing inversion artefacts using both damping and smoothing. From tests using synthetic data, we conclude that the simultaneous inversion scheme can improve resolution and can be applied to velocity models with a reasonably complex structure. The simultaneous inversion scheme has been successfully applied to coincident seismic reflection and refraction data recorded by the SAGE program in 1990-1991 in the western boundary area of the Rio Grande rift near Abiquiu, New Mexico. In this example, the simultaneous inversion derived a velocity model in which stratigraphic units and extensional fault blocks can be resolved.

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The analysis of constraint effects in fatigue crack growth in multi-layer structures is discussed. The process of material separation under cyclic loading is described by a cohesive zone model (CZM) with an irreversible constitutive relationship. The traction-separation behavior does not follow a predefined path, but is dependent on the evolution of the damage dependent cohesive zone properties. A modified boundary layer model is used in simulations of fatigue crack growth along the centerline crack of the metal layer sandwiched between two elastic substrates. Fatigue crack growth is computed for a series of values of metal layer thickness under constant and variable amplitude loading conditions. The results of the computations demonstrate that certain combinations of load magnitude, layer thickness and material properties results in significant constrain effects in fatigue crack growth. The influence of these constraint effects on fatigue crack growth rates and on crack closure processes is determined. The evolutions of the traction-separation law, the accumulated and current plastic zones, as well as the stress fields during the crack propagation are discussed.

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