Tomographic inversion and resolution for Rayleigh wave phase velocities in the Pacific ocean.

Abstract

Phase velocities of Rayleigh waves at periods between 60 and 200 s are measured by using IDA network data, and are inverted to the phase velocity distribution in the Pacific. We apply ART (Algebraic Reconstruction Technique) for the inversion without any a priori regionalizations.In order to estimate the resolving power of our data for the lateral heterogeneity, we use the Backus-Gilbert method. At 60-120 s the lateral variations of the velocities are strongly correlated with the sea floor age or surface tectonics, while such a correlation is weak at 150-200 s. As the period increases, the amplitude of the heterogeneity decreases in most parts of the Pacific. The marginal sea regions have more complicated features than the normal Pacific Ocean. In the Philippine Sea region, the velocities are lower at short periods than the average of the Pacific, but the sign of the heterogeneity is reversed at long periods. This feature may suggest that a cold slab descending beneath this region shows up at long periods. The Aleutian Sea and the Tasman Sea are slow, at 60-200 s. This regional difference in velocities may be due to the difference in geometries of the descending slabs.

Recent Seismological Studies on Upper Mantle Structure.

“…The magnitude of the anisotropy reaches 3% at 60s and it decreases with increasing period. The lateral heterogeneity obtained with azimuthal anisotropy is quite similar to that without anisotropy by Suetsugu and Nakanishi (1985). Their results were in good agreement with Montagner and Tanimoto (1990) in the entire Pacific, but inconsistent with Nishimura and Forsyth (1989) who suggested a correlation with fossil seafloor spreading direction rather than the direction of the present-day plate motion.…”

Three-dimensional modelling of upper mantle structure under the Pacific Ocean and surrounding area

“…Similar attempts have been made previously (e.g. Mikchell & Yu 1980;Suetsugu & Nakanishi 1985;Nishimura & Forsyth 1985, 1988), but we have at least twice as many paths as any of those studies. This has led to the discovery of some new features, such as the low-velocity anomaly under the Hawaii islands.…”

“…Montager 1986;Nishimura & Forsyth 1985, 1988Suetsugu & Nakanishi, 1985), and global studies (e.g. Woodhouse & Dziewonski 1984;Nataf et nl.…”

Collaborative Research: High-Resolution Seismic Velocity and Attenuation Models of Western China

“…The result is regularized by using a nine-point spatial smoothing, which was used in Q Lg tomography by Suetsugu and Nakanishi (1985) and Xie and Mitchell (1990). If k(p, q) denotes the kth cell, where p and q are cell numbers in the latitude and longitude directions, respectively, a set of regularization equations are organized by counting all neighboring cells of the kth cell to build a matrix L: .…”