Correlation Migration Using Gaussian Beams of Scattered Teleseismic Body Waves

Abstract

Correlation migration for structural imaging using Gaussian beams is described for the inversion of passively recorded teleseismic waves. Gaussian beam migration is based on an overcomplete frame-based representation of the seismic wave field and uses localized slant-stack windows of the data. Paraxial Gaussian beams are then utilized for the backpropagation of the seismic waves into the medium. The method can provide stable imaging of seismic data in smoothly varying background media where caustics and triplicated arrivals exist. We develop Gaussian beam migration for structural imaging, which allows for incident teleseismic waves from beneath the structure, using directly scattered or surface-reflected phases. The method is applied to synthetic data computed for a collisional-zone model, and the inversions show that the Gaussian beam migration can image structure using passive teleseismic data. The method is next applied to synthetic data that have been convolved with an observed pulse from the 1993 Cascadia experiment. The autocorrelation is computed and the autocorrelated data are migrated by using Gausian beams for direct P-to-S scattered waves and surface-reflected waves. Although the migrations of the autocorrelation data with the source pulse included have more noise than the migrations of the impulsive source data, the subduction zone structure can still be clearly identified in the migrated results without removal of the source pulses.

Imaging Offsets in the Moho: Synthetic Tests using Gaussian Beams with Teleseismic Waves

“…For the sake of brevity, we introduce the salient points of the GB migration below and a brief review of GB in the Appendix. A more complete, quantitative overview of GB migration appears in NOWACK et al (2006).…”

“…The Gaussian beam imaging formulation for the scattering of SV -waves from heterogeneities illuminated by incident P -waves can be obtained by applying the adjoint of the Born-approximation operator and expanding the scattered SV -waves into Gaussian beams (for more details, see NOWACK et al, 2006): Vol. 164, 2007 Imaging Offsets in the Moho…”

Global‐phase seismic interferometry unveils P‐wave reflectivity below the Himalayas and Tibet

“…This illumination range suffices to retrieve the zero‐offset (the zero‐offset response is the response that would be measured if there were a coinciding source and receiver at the free surface) reflection response R ( , , t ) from horizontal and gently dipping interfaces. Nowack et al [2006] applied autocorrelation, prior to migration, to only a single teleseismic phase and showed that still an acceptable image could be obtained in a setting with steeply dipping structure.…”

Forward modelling the multiply scattered 2.5-D teleseismicPwaves accelerated by the multilevel fast multipole method

“…6), which is an idealized 2‐D heterogeneous lithosphere introduced by Shragge et al (2001). A low‐velocity crust overlies a high‐velocity mantle whereas an old (remnant) high velocity crust is pushed under (Nowack et al 2006). Consistent with the perturbation theory, we use a two‐layer half‐space to model the 1‐D reference structure.…”