Descent of the ancient Farallon slab drives localized mantle flow below the New Madrid seismic zone

Abstract

The great earthquake sequence that occurred in the central Mississippi River Valley during the winter of 1811–1812 is unprecedented in the historical record of seismicity within stable continental plate interiors. We show, using viscous flow models based on high resolution seismic tomography, that the descent of the ancient Farallon slab into the deep mantle beneath central North America induces a highly localized flow directly below the New Madrid seismic zone (NMSZ). This localization arises because of structural variability in the Farallon slab and the low‐viscosity of the sub‐lithospheric upper mantle, and it represents a heretofore unrecognized and possibly significant driving mechanism for the enigmatic intraplate seismicity.

Western US intermountain seismicity caused by changes in upper mantle flow

“…However, our analysis suggests that intraplate seismicity may be determined by the interplay of active mantle upwellings and lithospheric heterogeneity, reconciling 'deep' 8,10,13 and 'shallow' 2,3,6 points of view on the origin of crustal deformation. GPE gradients themselves appear to play a minor part in driving seismicity in this region; rather, high GPE zones seem to mark domains that are buoyed by deep mantle flow 15 and so primed for extensional failure.…”

“…Present-day active mantle flow may also play a part, and a link between large-scale downwellings and intraplate seismicity was suggested for the 1811/1812 New Madrid (M < 7) earthquakes, for example 10 . Advances in structural seismology 3,11,12 now allow calculations of mantle flow on the scales appropriate for our study region 13 .…”

High-resolution Earthquake Relocation in the New Madrid Seismic Zone

“…Dextral slip on NE-trending faults and reverse slip on NW-trending faults within the NMSZ is con sistent with the present regional stress field, with the maximum compression axis oriented between 70 and 80° (Ellis 1994;Grana and Richardson 1996;Johnson 2008). Why the NMSZ generates high levels of microseismicity, while other ancient fault systems that are also optimally oriented within the present-day stress field do not, remains an open question (Liu et al 1992;Pollitz et al 2001;Forte et al 2007).…”

Eroding dynamic topography

“…Revisiting poorly understood aspects of the geological record combined with sophisticated modeling of mantle flow has recently led to renewed interest in constraining and quantifying the dynamic contribution to surface topography [Mitrovica et al, 1989;Gurnis et al, 2000;Conrad and Gurnis, 2003;Forte et al, 2007;Hartley et al, 2011]. A summary of recent investigations on the subject can be found in Braun [2010].…”