HR: 09:45h
AN: T31D-08    [Abstracts]
TI: Dynamic topography above retreating subductions systems. Theory, bathymetry, tomography gravity.
AU: * Husson, L
EM: lhusson@mit.edu
AF: Massachusetts Institute of Technology, EAPS 54-827 77 Mass. Ave., Cambridge, MA 02139 United States
AU: Royden, L H
EM: lhroyden@mit.edu
AF: Massachusetts Institute of Technology, EAPS 54-827 77 Mass. Ave., Cambridge, MA 02139 United States
AB: Because dense masses tend to sink in the asthenosphere, subsequent stresses should deflect the surface of the Earth above subduction zones. Our theoretical Stokeslet model predicts deflections in the order of 2000 m due to the viscous stresses associated with subduction. The bathymetry of oceanic back-arc basins like the Scotia sea or the Mariana basin increases towards the center of the basin by several hundred meters, while one expects to observe a typical age-subsidence relationship. The Aegean sea also shows a >1000 m increase in the bathymetry beneath the Cretan sea which is not isostically compensated. All three basins therefore have a bathymetry that appears to be at least partly non isostatic. The conversion of P-wave velocities into a density field allows the deflection of the surface of the Earth to be estimated. For the three case studies (East Scotia, Mariana, and Aegean Sea), well defined predicted deflections match the observed deflections of the bathymetry. Gravity data also indicate the presence of dense subducting slabs at depth. The large gravity anomaly estimated from seismic tomography is compensated by the dynamic deflection of the bathymetry. We conclude that the bathymetry of upper plates above retreating subductions is dynamically lowered by up to 1500-2000 m due to the viscous stresses of subductions.
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8122 Dynamics: gravity and tectonics
DE: 8164 Stresses: crust and lithosphere
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
DE: 8180 Tomography (6982, 7270)
SC: Tectonophysics [T]
MN: Fall Meeting 2005