Converted-wave Elastic Reverse Time Migration Imaging of the Pacific Northwest

We use a newly developed 3D elastic reverse time migration (RTM) imaging algorithm based on the Helmholtz decomposition to test approaches for imaging the shallow (< 50 km) descending Juan de Fuca slab in the Pacific Northwest. Seismic imaging conditions are constructed by breaking down the seismic wavefield into its constituent P and S components via the Helmholtz decomposition and backpropagating the decomposed wavefields. This allows us to focus on particular converted-wave scattering geometries, e.g., incident S to scattered P, which may be expected to have dominant signals in any given data set. The method is intended to be applied to dense seismic array observations where array analysis is expected to isolate useful scattered wave energy before implementation in RTM. We first demonstrate that our technique can successfully recover the structure of synthetic target models by using Helmholtz decomposition on synthetic seismic data and backpropagating the decomposed P and S wavefields to obtain elastic RTM images. We also present potential array geometries for collection of seismic data to be used for construction of 3D elastic RTM images of the Pacific Northwest.