Dr. Kelin Wang (Geological Survey of Canada)

2005.06.08

Tiele：　Submarine sedimentary wedges in subduction earthquake cycles:
　　　　　　the theory of dynamic critical taper

Abstract
　The conventional theory of critically tapered Coulomb wedges addresses
geological-timescale processes. In this work, we expand the conventional
theory to include the process of great earthquakes. The new theory, called
the dynamic critical taper theory, allows us to study mechanical and fluid
regimes of submarine wedges at the century timescale. Building on the
perfectly Coulomb-plastic wedge rheology assumed in the conventional theory,
we assume an elastic - perfectly Coulomb-plastic rheology. The new theory
states that the severely deformed, most seaward part of submarine wedges,
called the outer wedge, overlies the updip velocity-strengthening part of
the subduction fault, and the less deformed inner wedge overlies the
velocity-weakening part - the seismogenic zone. During great earthquakes,
the outer wedge is pushed into a compressively critical state, with sharp
increase in horizontal stress and pore fluid pressure. The outer-wedge
geometry is controlled by the peak stress of the velocity-strengthening part
of the subduction fault achieved in largest great earthquakes. After the
earthquake, the outer wedge returns to a stable state, with stress and fluid
pressure both decreasing with time. The inner wedge stays in the stable
regime throughout the earthquke cycles. In this seminar, I will introduce
the new theory and explain its implications to the studies of the updip
limit of the seismogenic zone, activation of splay faults, coseismic
seafloor deformation and tsunami generation, evolution of the fluid regime,
and forearc stress and structure. The theory will be applied to the IODP
NanTroSeize transect, among other examples.