Episodic Slow Slipping of Seafloor under Cascadia: What Physical Processes cause Aseismic Deformation Transients?

  • Date: 02/12/2007

James Rice (Harvard University)


University of British Columbia


In several shallow-dipping subduction zones, including Cascadia, the
seafloor undergoes episodes of more rapid than usual creep-slippage
under the overlying margin, but at rates vastly slower than usual
earthquake slip. In some locations, also including Cascadia,
non-volcanic seismic tremors occur during the slip episodes. Graduate
student Yajing Liu and I have been trying to understand what physical
processes underlie these phenomena. We have shown that transients, with
features somewhat like the observations, are a natural outcome of
modern 'rate and state' formulations of fault zone friction, in a
regime for which the ambient fluid pore pressure within the fault zone
is very high and close to the compressive normal stress clamping the
fault walls together. Evidence for such pressure conditions is provided
by independent mechanical and petrological constraints.

James R. Rice, a professor of Engineering Sciences and Geophysics at
Harvard, born in 1940, addresses problems in theoretical mechanics as
they arise in the geological sciences, particularly in seismology and
the science of earthquakes, as well as in civil/environmental
engineering and materials physics. His earthquake studies are on the
mechanics and physics of fault zone processes.

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