Local earthquake tomography between rays and waves: fat ray tomography

The limitations of ray-based forward solutions in seismic tomography are th eoretically well known. To correctly represent the physical forward problem in seismic tomography, application of full three-dimensional (3-D) wave th eory would be required. Up to now this is not possible for the size of a ty pical local earthquake study. With the concept of fat rays resembling the w aves Fresnel volume, a more complete, physically consistent and accurate so lution to the forward problem is available. In this paper. we present an ap proach to include Pat rays in local earthquake tomography, called Fatomo. T he comparative study with synthetic data and inversion results with Fatomo and a ray-based approach to local earthquake tomography, SIMULPS, reveals n ew insights into the role of resolution and model parameterization in local earthquake tomography. Intuitively expected effects of fat rays on resolut ion estimates, such as higher node sampling values and lower resolution dia gonal element values for wider fat rays can be seen in the results. For ide al model parameterization, differences between fat ray and ray tomography a re small. Our results document, however, that the influence of model parame terization is less critical for fat ray tomography than for ray tomography. (C) 2001 Elsevier Science B.V. All rights reserved.