Surface waveform tomography of the upper mantle under the south Pacific super-swell from analysis of "PLUME" broad-band data
Abstract
PLUME (Polynesian Lithosphere and Upper Mantle Experiment) is a multidisciplinary project funded by the French Ministry of Research, which aims to image the upper mantle structure beneath French Polynesia. The area is characterised by a swarm of volcanic island chains -- the Society Islands, Austral Islands, and Marquesas -- superimposed on a broad topographic high known as the South Pacific super swell (McNutt, 1998). The region is also characterised by a large-scale, low velocity anomaly in the lower mantle (e.g. Su et al., 1994) and anomalous converted phases from the 660 km discontinuity (Vinnik et al., 1997). We present preliminary results of a surface wave tomographic study of the region. Except in its southernmost part, the Pacific plate is surrounded by subduction zones that provide an excellent azimuthal distribution of deep events with well excited overtones. The station distribution around the margins of the Pacific is also relatively dense, due to the high seismic risk of these regions. The resulting dense ray coverage, however, thins out in the South Pacific, and is insufficient for high-resolution imaging of the Pacific super plume. As part of the PLUME experiment, ten broadband stations have been deployed in French Polynesia, as far as -27 degrees South. The stations provide the necessary data to the south of the main location of the super swell to facilitate high-resolution imaging of its upper mantle expression. We initially analyse only Rayleigh wave seismograms, which constrain the isotropic SV structure of the upper mantle. Our preliminary results, obtained using the automated (Debayle, 1999) version of the Cara and Leveque (1987) method, will help answer questions about the possible existence and/or morphology of upper mantle upwelling (plume?) connecting with the Pacific super swell.
- Publication:
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EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....3442M