Teleseismic shot-profile migration
The shot-profile migration approach of wave-equation migration generates subsurface images using the interferomet- ric principle of crosscorrelating two passive wavefields. These wavefields are typically a source wavefield containing energy from an excited source and a receiver wavefield comprised of scattered-source wavefield energy by the discontinuous earth structure. Shot-profile migration can be recast as a novel way of imaging the earth’s lithosphere using teleseismic wavefield data, where the source wavefield is the directly arriving wavefront and the receiver wavefield is the following wavefield coda. We demonstrate that the shot-profile technique can be tailored to suit teleseismic acquisition geometry and wavefields. Assuming an acoustic framework and 2.5D experimental geometry, we develop procedures that enable kinematic and structural imaging (migration) using both transmission and free-surface reflected passive wave- fields. Experiments with synthetic data demonstrate the method’s applicability and illustrate the negative imaging consequence of using inaccurate migration velocity profiles. We apply shot-profile migration to a suite of teleseismic events acquired during the IRIS-PASSCAL CASC-1993 experiment in central Oregon. The imaging results are interpreted to show the Juan de Fuca plate subducting beneath the North American plate. We attribute the observed dissimilarities between these results and other Juan de Fuca subduction- zone images to the combination of different imaging goals and the use of more accurate migration velocity profiles.