Anisotropic tomography of the Atlantic Ocean from Rayleigh surface waves

Details Anisotropic tomography of the Atlantic Ocean from Rayleigh surface waves Anisotropic tomography of the Atlantic Ocean from Rayleigh surface waves

Apr 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998pepi..106..257s&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 106, Issue 3-4, p. 257-273.

Physics

8

Scientific paper

The depth extent of the Mid Atlantic Ridge and the role of hotspots in the Atlantic opening are still a matter of debate. In order to constrain the structure and the geodynamic processes below the Atlantic Ocean, we provide the first anisotropic phase velocity maps of this area, obtained at a regional scale. We have determined Rayleigh wave phase velocities along 1311 direct epicentre to station paths. For each path, phase velocities are calculated by a technique of cross-correlation with a synthetic seismogram. These phase velocities are corrected for the effect of shallow layers. They are then inverted, without a priori constraints, to obtain maps of the lateral variations of the anisotropic phase velocities in the period range 50-250 s. The ridge axis corresponds to a low velocity anomaly, mainly visible at short periods. A good correlation between hotspot locations and low velocity anomalies is obtained for the whole period range. Furthermore, a low velocity anomaly elongated along a North-South direction is visible for every period and seems to be correlated with hotspot positions. On average, the North Atlantic is associated with higher velocities than the South Atlantic. The shields below Canada, Brazil and Africa display high velocity anomaly at short periods and only the Brazilian and African shields are still visible for a period of 200 s, thus suggesting that the Canadian shield is a shallower structure. The maps of phase velocity anisotropy under the Atlantic Ocean are interpreted in the Mid-Atlantic area, where we have the best resolution. Close to the ridge, the fast axis of Rayleigh wave phase velocity is found perpendicular to the ridge axis. A comparison of anisotropy directions and plate motion shows that seismic anisotropy integrates also deeper phenomena such as mantle convection.

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