HR: 16:15h
AN: T54C-02 INVITED    [Abstracts]
TI: Deep Mantle Dynamics under the North American Continent Drives Localised Flow and Stress Below the New Madrid Seismic Zone
AU: * Forte, A M
EM: forte.alessandro@uqam.ca
AF: GEOTOP -- Dept. Sci. Terre & Atmosphère, Université du Québec à Montréal, CP 8888, Succ. Centre-ville, Montréal, QC H3C 3P8, Canada
AU: Mitrovica, J X
EM: jxm@physics.utoronto.ca
AF: Department of Physics, University of Toronto, 60 St. George Street, Toronto, ON M5S 1A7, Canada
AU: Moucha, R
EM: moucha@sca.uqam.ca
AF: GEOTOP -- Dept. Sci. Terre & Atmosphère, Université du Québec à Montréal, CP 8888, Succ. Centre-ville, Montréal, QC H3C 3P8, Canada
AU: Simmons, N A
EM: simmons27@llnl.gov
AF: Lawrence Livermore National Laboratory, Seismology Group, 7000 East Avenue, Livermore, CA 94550, United States
AU: Grand, S P
EM: steveg@maestro.geo.utexas.edu
AF: Jackson School of Geosciences, University of Texas at Austin, 1 University Station, Austin, TX 78712, United States
AB: The origin of intraplate earthquakes represents one of the outstanding problems in modern geophysical research, and the major earthquake sequence that struck the central Mississippi River Valley in 1811-1812, the so-called New Madrid seismic sequence, has become a principal target of this research. As Johnston and Schweig (1996) have noted, the occurrence of such large magnitude earthquakes in "stable" North American crust, far from any plate boundaries, remains an enigma. To understand the possible origin of this enigmatic seismic activity we have developed a new high resolution model of mantle flow below North America. The model is constrained by simultaneously inverting global seismic and mantle-convection data sets and it includes an explicit treatment of the positive chemical buoyancy of the continental tectosphere. Moreover, it adopts a depth dependent mantle viscosity structure which reconciles both glacial isostatic adjustment (GIA) and convection data. The flow model successfully reproduces plate velocities and observations of surface gravity and topography, including the continent-scale quasi-linear depression (after corrections for GIA and crustal heterogeneity) extending from northern Alaska to Venezuela. The predictions also match lithospheric flow and stress fields inferred from local and regional measurements of seismic anisotropy and surface deformation. We demonstrate that these signals are largely driven by viscous flow coupled to density anomalies within the lower mantle associated with the descent of the ancient Kula-Farallon plate system. More importantly, the flow calculations elucidate how these large-scale heterogeneities give rise to flow and stress patterns below the New Madrid Seismic Zone which are favourably oriented with respect the local fault geometry in this portion of the Mississippi valley.
DE: 8110 Continental tectonics: general (0905)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8166 Stresses: deep-seated
DE: 8180 Tomography (6982, 7270)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting