Modelling 2D complex anomalies by seismic tomography (detection and delineation of anomalies with sharp boundaries)

In seismic tomography an important task is to delineate the shape and geometry of anomalies with sharp boundaries. This is especially true when building structures are investigated. In this paper properties and characteristics of some seismic inversion algorithms to individuate the best one for solving such a problem are analyzed. At first, some considerations about the inversion theory are discussed, then the inversion programs used are described in detail and two new algorithms are implemented. For a better understanding of the problem, a synthetic example is carried out. Finally, a seismic tomography survey is performed to asses the thickness of a brick wall that forms the sides of a flowerpot. The inversion of the collected data set of both the synthetic model and the field survey are performed by all the algorithms considering straight ray path approximation, and results are discussed and compared. The use of a variable damping factor seems to be a good method to determine anomalies for reducing ghosts and artefacts. The new algorithms permit us to insert a starting model and the use of inequality constraint in such a way that the results better approximate a realistic model. In the field survey a comparison with ray tracing is made.