The Advantages of Sp Pre-stack Migration Based on Scattering Kernels
Abstract
Sp receiver functions have been widely used to detect the lithosphere-asthenosphere boundary (LAB) and other mantle discontinuities, as the Sp phase is not contaminated by crustal reverberations. However, traditional common-conversion point (CCP) stacking can be biased by the assumption of horizontal layers, and typically fails to continuously image structures that dip at more than 10˚. A new pre-stack migration method based on recently developed Sp scattering kernels offers an alternative that more accurately captures the timing and amplitude of scattering. When calculating kernels, Sp-S times are estimated with the fast-marching method, and scattering amplitude versus direction, geometrical spreading and phase shifts are accounted for. To test the kernel-based stacking (KBS) method, synthetic Sp phases were predicted using SPECFEM2D (Tromp et al., 2008) for velocity models with a flat Moho and a LAB with a ramp structure. To minimize spatial aliasing with larger station spacing (e.g. 50 km), Sp receiver functions were interpolated to more closely spaced pseudostations using either spatial averaging (Neal and Pavlis, 1999) or compressive sampling (Herrmann and Hennenfent, 2008). Synthetic data show that compressive sampling more accurately recovers the original wavefield. The KBS method resolves horizontal interfaces equally well as CCP stacking, and outperforms CCP stacking when imaging dipping boundaries, but dip resolution is still limited. Several adjustments to the method offer additional improvement, including use of more vertically incident phases such as SKSp, and limiting the kernels to only those portions that are most sensitive to structures with a given dip. However, a third approach, which is more practical with unknown structure, is to determine the portions of the kernels that have the greatest positive interference among neighboring stations, and to downweight these points, thus enhancing scattering from dipping structures where positive interference is lower. With this modification, the KBS method expands the range of continuously well-resolved LAB dip to 15˚. However, the intrinsic properties of teleseismic Sp phase kernels limit their ability to resolve more steeply dipping LAB structures. We are now developing a 3D version of KBS that will be applied to real data.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.S51A..05H
- Keywords:
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- 7260 Theory;
- SEISMOLOGYDE: 7270 Tomography;
- SEISMOLOGYDE: 7290 Computational seismology;
- SEISMOLOGY