Can finite‐frequency effects be accounted for in ray theory surface wave tomography?

Abstract

[1] We present a series of synthetic tests showing that regional surface wave tomographies with a dense path coverage of the target region can be safely conducted under ray theory because the shortcomings of ray theory in considering finite-frequency effects can be counterbalanced by a physically-based regularization of the inversion. In particular, we show that with ray theory applied under the above conditions, it is possible to detect heterogeneities with length scales smaller than the wavelength of the data set.

Lateral Variations of Rayleigh-Wave Dispersions in the Philippine Sea Region

“…A few studies stressed that tomographic results using the finite-frequency theory are superior to those using the traditional ray theory (a great-circle path assumption under high-frequency approximation) (e.g., Zhou et al 2005). However, other studies (Sieminski et al 2004;Levshin et al 2005;Trampert and Spetzler 2006) found that results using the ray theory are similar to those of the finite-frequency theory when utilizing reasonable ray coverage in the study region. Sieminski et al (2004) further pointed out that finite-frequency effects can be counterbalanced by a physically-based regularization of the tomographic inversion or dense ray coverage in the study region (e.g., Levshin et al 2005).…”

“…However, other studies (Sieminski et al 2004;Levshin et al 2005;Trampert and Spetzler 2006) found that results using the ray theory are similar to those of the finite-frequency theory when utilizing reasonable ray coverage in the study region. Sieminski et al (2004) further pointed out that finite-frequency effects can be counterbalanced by a physically-based regularization of the tomographic inversion or dense ray coverage in the study region (e.g., Levshin et al 2005). Trampert and Spetzler (2006) also stated that tomographic models from finite-frequency theory and ray theory are statistically similar.…”

“…Sieminski et al 2004;Levshin et al 2005;Trampert and Spetzler 2006). Also, the relationship between lateral velocity variation and azimuthal variation is weak (cf.…”

“…Trampert and Spetzler (2006) also stated that tomographic models from finite-frequency theory and ray theory are statistically similar. Experiments of Sieminski et al (2004) stressed that regional surface-wave tomography can be safely conducted using the great-circle ray theory assumption when good path coverage and short path length are used. Additionally, regarding elastic anisotropy effect on surfacewave tomography, Suetsugu and Nakanishi (1987) stressed that the trade-off between lateral velocity variation and azimuthal variation is weak.…”

The state of the upper mantle beneath southern Africa

“…Ritzwoller et al (2002) examined the effects of off-great circle propagation and found that for short path lengths (∼5000 km) such as those primarily used in this study, the great circle assumption was adequate but led to increasing bias in the inverted model as path length increased. Sieminski et al (2004) show that using a dense path coverage of relatively short paths and assuming ray theory, it is possible to detect heterogeneity with length scales smaller than the wavelength of the data set. We therefore have restricted our analysis to relatively short paths (≤6000 km) compared to those used in global studies.…”