Global upper‐mantle structure from finite‐frequency surface‐wave tomography

Abstract

Journal of Geophysical Research, v. 111, n. B4, p. 24 pp, 2006. http://dx.doi.org/10.1029/2005JB003677International audienceWe report global shear-wave velocity structure and radial anisotropy in the upper mantle obtained using finite-frequency surface-wave tomography, based upon complete three-dimensional Born sensitivity kernels. Because wavefront healing effects are properly taken into account, finite-frequency surface-wave tomography improves the resolution of small-scale mantle heterogeneities, especially for deep anomalies that are constrained by the longest-period surface waves. In our finite-frequency model FFSW1, the globally averaged radial anisotropy shows a transition from positive (SH > SV) to negative anisotropy (SV > SH) at about 220 km, consistent with a change in the dominant mantle circulation pattern from predominantly horizontal flow at shallow depths to vertical flow at greater depths. The radial anisotropy beneath cratons and the old Pacific plate agrees well with previous studies. However, our model exhibits a strong negative radial anisotropy at depths greater than 120 km beneath mid-ocean ridges, a feature that is not present in previous upper-mantle models. More interestingly, the depth extent of the ridge anomalies is distinctly different beneath fast- and slow-spreading centers; anomalies beneath fast-spreading centers are stronger, but the strength decreases rapidly below 250 km. In contrast, beneath slow-spreading centers such as the northern Mid-Atlantic Ridge and the Red Sea, anomalies extend down at least to the top of the transition zone. The different depth extent of the ridge anomalies suggests that the primary driving force of slow-spreading seafloor may be different from that of fast-spreading seafloor and that active upwelling beneath slow-spreading ridges may play a major role in the opening of the seafloor

The European Upper Mantle as Seen by Surface Waves

“…In this endeavour, finite-frequency effects in wave propagation, neglected here, will ultimately have to be taken into account (Dahlen et al 2000;Zhou et al 2006;Fry et al 2008;Peter et al 2008). With this study we have proven the effectiveness of fundamentalmode surface-wave data, and of our multiple-resolution algorithm, at resolving the intermediate-scalelength distribution of regional upper-mantle heterogeneity.…”

“…It remains unclear to what extent this limit can be outdone through the application of finite-frequency methods (Li and Romanowicz 1996;Dahlen et al 2000;Spetzler et al 2001;Zhou et al 2006). Peter et al (2008) compared ray-theoretical and finite-frequency tomographies based on the Rayleigh-wave component of our database.…”

Geodynamic Activity of Modern Structures and Tectonic Stress Fields in Northeast Asia

“…Мантия под бассейном Северного Ледовитого океана характеризуется относительно высокими скоростями сейсмических волн -до ~150 км, а с увеличением глубины -пониженными скоростями по отношению к прилегающим терри-ториям, о чем также свидетельствуют особенности распределения групповых скоростей поверхност-ных волн [Levshin et al, 2001]. Практически все рас-сматриваемые модели демонстрируют локальный минимум скоростей, приуроченный к спрединго-вому хребту Гаккеля, причем с увеличением глуби-ны данная особенность становится более выра-женной [Zhou et al, 2006].…”

“…Thickness of the crust from CRUST 1.0 model [Laske et al, 2013]. ных в вертикальной и горизонтальной плоскостях, и получаемых путем интерпретации дисперсион-ных кривых волн Рэлея и Лява соответственно, яв-ляется положительной [Shapiro, Ritzwoller, 2002;Zhou et al, 2006], а в интервале глубин 250-400 км проявляются достаточно обширные области, при-уроченные к зонам субдукции и хребту Гаккеля, с отрицательной анизотропией (V SH <V SV ), свидетель-ствующей о наличии вертикальных течений в ман-тии.…”

A method for inversion of layered shear wavespeed azimuthal anisotropy from Rayleigh wave dispersion using the Neighborhood Algorithm

“…These studies are important for understanding shape or lattice preferred orientations of minerals and deformation styles in the crust and upper mantle (Savage 1999;Mainprice 2007;Montagner 2007). For instance, Shapiro and Ritzwoller (2002) and Zhou et al (2006) used earthquake Rayleigh and Love waves to obtain global models of shear wavespeed radial anisotropy in the upper mantle, that is, the difference between the vertically polarized shear wavespeed (V SV ) and the horizontally polarized shear wavespeed (V SH ). Ambient noise tomography using both Rayleigh and Love waves can produce high-resolution shear wavespeed radial anisotropy in the crust (e.g., Huang et al 2010;Moschetti et al 2010;Guo et al 2012;Luo et al 2013).…”