Sequential integrated inversion of refraction and wide-angle reflection traveltimes and gravity data for two-dimensional velocity structures

A new algorithm is presented for the integrated 2-D inversion of seismic tr aveltime and gravity data. The algorithm adopts the 'maximum likelihood' re gularization scheme. We construct a 'probability density function' which in cludes three kinds of information: information derived from gravity measure ments; information derived from the seismic traveltime inversion procedure applied to the model; and information on the physical correlation among the density and the velocity parameters. We assume a linear relation between d ensity and velocity, which can be node-dependent; that is, we can choose di fferent relationships for different parts of the velocity-density grid. In addition, our procedure allows us to consider a covariance matrix related t o the error propagation in linking density to velocity. We use seismic data to estimate starting velocity values and the position of boundary nodes. S ubsequently, the sequential integrated inversion (SII) optimizes the layer velocities and densities for our models. The procedure is applicable, as an additional step, to any type of seismic tomographic inversion. We illustrate the method by comparing the velocity models recovered from a standard seismic traveltime inversion with those retrieved using our algori thm. The inversion of synthetic data calculated for a 2-D isotropic, latera lly inhomogeneous model shows the stability and accuracy of this procedure, demonstrates the improvements to the recovery of true velocity anomalies, and proves that this technique can efficiently overcome some of the limitat ions of both gravity and seismic traveltime inversions, when they are used independently. An interpretation of field data from the 1994 Vesuvius test experiment is a lso presented. At depths down to 4.5 km, the model retrieved after a SII sh ows a more detailed structure than the model obtained from an interpretatio n of seismic traveltime only, and yields additional information for a furth er study of the area.