Directional Mantle Flows Under the Oceans: A Joint Analysis of Seismic, Gravity and Bathymetry Data

Abstract:

Deciphering mantle flow patterns and their interplay with lithospheric motions remains a debated question. Because they are driven by density anomalies and dynamically deflect Earth's internal interfaces, such flows are expected to contribute to geoid and topography variations. By modifying the thermal structure of the lithosphere, they may also influence the subsidence of oceanic plates.

Over the oceans, geoid undulations in a wide range of wavelengths, and regional variations of the subsidence, have been evidenced since the advent of satellite altimetry. The existence of a directional geoid fabric along the plate motions, in a range of scales up to 2000 km, has been confirmed over the Pacific ocean by a recent analysis of GRACE satellite gravity data (Hayn et al., 2012). Consistently, a shear velocity model of the upper mantle, SEMum2 (French et al., 2013), indicates the presence of low shear velocity channels extending horizontally in the upper mantle. Oriented along the absolute plate motion, they are found under all oceans.

In order to understand the nature of these channels, and characterize the flows at different scales below the Pacific and Atlantic oceans, we perform a joint analysis of seismic, geoid and bathymetry data. First, we isolate the geoid and bathymetry directional signal at different spatial scales using a gradients analysis. Then, we carry out sensitivity tests and compare the obtained signals to those based on seismic tomography results and different viscosity profiles. We discuss here our preliminary results.