HR: 16:00h
AN: T54C-01    [Abstracts]
TI: A Critical Stress State in Stable Continental Regions?
AU: * Hough, S E
EM: hough@gps.caltech.edu
AF: U.S. Geological Survey, 525 S. Wilson Avenue, Pasadena, CA 91106, United States
AU: Seeber, L
EM: nano@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Route 9W, Palisades, NY 91006, United States
AU: Stein, S
EM: seth@earth.northwestern.edu
AF: Northwestern University, 1850 Campus Drive, Evanston, IL 60208, United States
AB: Despite considerable study we still do not understand why stable continental region (SCR) earthquakes occur where they do. Although most earthquakes can be related to structural features such as failed rifts, SCR regions contain many such features, few of which are active. Previous studies have suggested that SCRs are characterized by a critical stress state, such that stress in the upper crust is pervasively close to the failure stress of faults. We present a simple rheological model incorporating stress-dependent aseismic deformation that can explain how a critical stress state can be maintained. In a low strain-rate environment, even a low rate of aseismic deformation can significantly reduce the accumulation of stress available to drive earthquakes. Given a low strain-rate and a high failure stress, we show that it is possible to accommodate all strain by permanent deformation. However, one is left with the apparent paradox that, while borehole measurements suggest that intraplate crust is everywhere critically stressed, earthquakes (and triggered earthquakes) appear to occur preferentially in certain regions. The question is, what, if anything, is unusual about these regions? Although some lines of evidence point to local stress concentrations and/or to locally weak faults, we note that the effects of stress interactions are expected to affect seismicity rates for longer periods than in SCRs, and may be a first- order control on observed earthquake distributions during a short historical record. Thus, while there is a relatively compelling association between failed rifts and large earthquakes, the basis of differentiation of hazard within or between presently active structures and those that appear inactive is likely to be less compelling than the historical record inclines us to believe.
UR: http://pasadena.wr.usgs.gov/office/hough/AGU2007
DE: 8103 Continental cratons
DE: 8107 Continental neotectonics (8002)
DE: 8123 Dynamics: seismotectonics
DE: 8164 Stresses: crust and lithosphere
SC: Tectonophysics [T]
MN: 2007 Fall Meeting