Scalar reverse‐time depth migration of prestack elastic seismic data

Abstract

Reflected P‐to‐P and P‐to‐S converted seismic waves in a two‐component elastic common‐source gather generated with a P‐wave source in a two‐dimensional model can be imaged by two independent scalar reverse‐time depth migrations. The inputs to migration are pure P‐ and S‐waves that are extracted by divergence and curl calculations during (shallow) extrapolation of the elastic data recorded at the earth’s surface. For both P‐to‐P and P‐to‐S converted reflected waves, the imaging time at each point is the P‐wave traveltime from the source to that point. The extracted P‐wave is reverse‐time extrapolated and imaged with a P‐velocity model, using a finite difference solution of the scalar wave equation. The extracted S‐wave is reverse‐time extrapolated and imaged similarly, but with an S‐velocity model. Converted S‐wave data requires a polarity correction prior to migration to ensure constructive interference between data from adjacent sources. Synthetic examples show that the algorithm gives satisfactory results for laterally inhomogeneous models.

Five ways to avoid storing source wavefield snapshots in 2D elastic prestack reverse time migration

“…This implies that P-and Swave separations that preserve their respective particle motions need to be performed prior to extrapolation (Sun and McMechan, 2001;Sun et al, 2004), or as part of the imaging condition (Sun et al, 2006). There are few algorithms for PS wavefield separation (Dellinger, 1991;Balch and Erdemir, 1994;Yan and Sava, 2007;Denli and Huang, 2008;Lu et al, 2010;Zhang and McMechan, 2010), many of which are based on divergence and curl calculations, and so do not preserve the input particle motion.…”

Multi-component elastic reverse time migration based on the P- and S-wave separated velocity–stress equations

“…Zhe and Greenhalgh (1997) used potentials instead of displacements to propagate P-and S-waves. Sun and McMechan (2001) proposed the scalar reverse time migration for elastic multi-component data. The approach first uses calculations of divergence and curl to separate multi-component data into pure P-and S-components.…”

An excitation potential imaging condition for elastic reverse time migration

“…Many researchers have previously explored this aspect (e.g., Baysal et al, 1983;Chang and McMechan, 1986, 1994Du and Qin, 2009;Levin, 1984;Sun and McMechan, 2001;Sun et al, 2006;Wapenaar et al, 1987;Sava, 2008, 2009;Yan and Xie, 2012;Yoon and Marfurt, 2006;Zhe and Greenhalgh, 1997). However, some problems still remained.…”

“…For example, when imaging with the vector displacement, a simple component-bycomponent operation (e.g., the cross-correlation operation under the cross-correlation imaging condition for vector wavefields) between source and receiver wavefields could lead to artifacts caused by crosstalk between the unseparated wave modes (Yan and Sava, 2008). However, this problem may be mostly alleviated by using the scalar and vector potentials of the elastic wavefield (Sun and McMechan, 2001;Sun et al, 2006;Sava, 2008, 2009;Zhe and Greenhalgh, 1997).…”

“…Zhe and Greenhalgh (1997) used the potential instead of the displacement to propagate P-and S-waves. Sun and McMechan (2001) proposed the scalar reverse time migration for elastic multicomponent data by first using calculations of divergence and curl to separate the multicomponent data into pure P and S components. Sun et al (2006) extended this method to 3D elastic data.…”