Seismic tomography of southern California 
Carl Tape 

We are in the process of obtaining new 3D compressional- and shear-wavespeed
models of southern California in a region approximately 600 km by 500 km by 60
km. Our tomography technique contains two key features. First, all the
synthetic seismograms are computed using a 3D spectral-element method based
upon a 3D southern California reference model. Second, we compute the gradient
of the misfit function between the observed and predicted seismograms by using
adjoint methods, which, for each event, involves a dynamic interaction between
two wavefields. Our first iteration of the model reveals that the wavespeed
structure outside the basins need to be decreased by at least 5 percent, while
the wavespeed structure within the basins needs to be slightly increased.
Further iterations of the 3D model will illuminate fine-scale features.