Abstract

Joint interpretation of disparate geophysical datasets is essential to deriving meaningful subsurface geologic models. Here we describe a method for joint inversion of first arrival travel time and gravity data with application to field data from a geologically complex subduction zone. We employ a layer-based model description, in which interfaces (which may also be called isovelocity lines) are defined by summation of arc-tangent functions. Within each layer, the velocity is assumed to vary linearly with depth at each surface location. Density is related to velocity using a fourth order polynomial whose coefficients are assumed known. The non-linear optimization problem is solved by a very fast simulated annealing (VFSA). We applied our technique to field data collected over the Ryukyu subduction zone offshore Taiwan during an ocean bottom seismometer (OBS) experiment (called TAICRUST) conducted in the year 1995. Application to one NS trending line resulted in acceptable fit of both travel time and gravity data. The resulting model clearly delineates the plate boundaries.