Multichannel inversion of scattered teleseismic body waves: Practical considerations and applicability

We investigate the resolving power and applicability of a recently developed technique for multichannel inversion of scattered teleseismic body waves recorded at dense seismic arrays. The problem is posed for forward- and back-scattered wavefields generated at discontinuities in a 2D isotropic medium, with the backprojection operator cast as a generalized Radon transform (GRT). The approach allows for the treatment of incident plane waves from arbitrary backazimuths, and recovers estimates of material property perturbations about a smoothly varying reference model. An investigation of the main factors affecting resolution indicates that: (1) comprehensive source/station coverage is necessary to optimize geometrical resolution and recover accurate material property perturbations; (2) the range in dip resolution diminishes with increasing depth and is inversely proportional to array width (e.g., reaches [-45°,45°] at depths equivalent to ∼1/2 array width); (3) distortion of the image due to spatial aliasing is only significant at depths ≤2 x [station spacing]; and (4) unaccounted for departures from model assumptions (i.e., isotropy and 2D geometry) result in defocusing and mismapping of structure. Two applications to field data are presented. The first considers data from the Abitibi 1996 broadband array, in which stations were deployed at ∼20 km intervals. Imaging results show that this level of spatial sampling, which is characteristic of modem broadband arrays, is sufficient to adequately resolve structure below mid-crustal depths. For these data, we introduce a new preprocessing algorithm that uses eigenimage decomposition of seismic sections to suppress wavefield contamination by PcP and PP phases. The second application involves short period data from the Los Angeles Region Seismic Experiment and shows that images obtained from high frequency records are subject to significant contamination by scattered surface waves.