Test of tectonic models by great circle Rayleigh waves

Abstract

A large set of published great circle Rayleigh wave phase velocities in the period range 125-350s is used to compare three recent tectonic models (Okal, UvEque, Jordan). Prior to any regionalization, the symmetry property of the great circle integrals is used to obtain a lower limit of the signal/noise ratio in the data. It turns out that the signal is responsible for at least 30 per cent of the data variance in the period range 175-300 s.A standard regression method is applied for computing the 'pure path' velocities and the model efficiency is derived from a variance analysis. It is shown that, even at great depth, none of the three models explains more than 60 per cent of the energy due to the long-wavelength lateral heterogeneities (A 2 6500 km).The three models have nearly the same efficiency for explaining the shortperiod data ( T -125s). Between 200 and 300s, the higher performance of Okal's model indicates that it is important to separate the subduction zones from the other orogenic zones. By perturbing the lateral extension of the subduction zones, it comes out that they constitute on both sides of the subducting slabs wider anomalies than often assumed, suggesting large downgoing flows. On the contrary, the effect of surface features such as marginal seas are restricted to a close region in front of the trenches. Finally, the anomalous ellipticity values deduced directly from great circle data are partly explained by a coupling between tectonics and ellipticity.

Normal modes of the Earth

“…[19], had claimed that the inner core had a different rotation rate than the mantle by about 3 • per year. However by comparing normal mode measurements over the last twenty years, Laske and Masters [13] found that this rotation difference is less than 0.13 • ± 0.11 • yr −1 , which is consistent with other seismic data [20] and with the idea that the inner core is gravitationally locked to the mantle. This issue is not completely solved yet.…”

Measurements of mantle wave velocities and inversion for lateral heterogeneities and anisotropy: 3. Inversion

“…Two continental types are defined: mountainous regions (M) and shields (S). This regionalization is successful in reducing the variance of great circle observations (Souriau and Souriau, 1983). The variance reduction for great circle phase velocity measurements amounts to about 80% for Rayleigh waves and 60% for Love waves for periods from 150 to 300 s (NA 1 ).…”

“…Depending on the appropriateness of the a priori choice, the way that great circle observations are actually explained varies. Souriau and Souriau (1983) have tested the variance reduction achieved by several proposed regionalizations and concluded that the regionalization of Okal (1977) was the best. It includes four oceanic regions corresponding to different age slices of the seafloor, a region for trenches and marginal seas, a shield region, and a mountainous region.…”

Anisotropic models of the upper mantle

“…oid ocean contained only Mitchell and Yu's data when the models were determined, However, the Rayleigh phase velocity data of Souriau and Souriau [1983] were added after the model was derived. These data, which fit the model already calulated to within two standard deviations, are based on a pure path analysis ut*ing the combined velocity data of Kanamori [1970], Dziewonski [1970], Wu [1972], Dziewonski and Gilbert [1972], Okal [1977], Nakanishi [1979], and Leveque [1983] were compared with the models, and generally agree with these except in the 50-100 M.Y, old province.…”