HR: 16:00h
AN: T24A-01 [Abstracts]
TI: Stress, Strain, and Mountain-Building in Central Japan
AU: * Townend, J
EM: john.townend@vuw.ac.nz
AF: School of Earth Sciences, Victoria University of Wellington
PO Box 600, Wellington, 6001
New Zealand
AU: Zoback, M D
EM: zoback@pangea.stanford.edu
AF: Department of Geophysics, Stanford University, Stanford, CA 94305-2215
United States
AB:
The work presented here has two key objectives: to investigate the geometric relationships between the principal directions
of crustal stress and crustal strain rate in central Japan; and to evaluate how tectonic stresses in the crust are related to
the rates of horizontal strain produced by different tectonic processes. Specifically, we consider the extent to which
tectonic stress directions reflect transient deformation produced by interseismic subduction thrust locking. The axis of
maximum horizontal compressive stress (SHmax) obtained from focal mechanism inversion agrees well with the axis
of greatest contractional strain rate (ε̇_3) in central and southwest Japan only after the effects of
interseismic strain accumulation on geodetic observations have been accounted for according to an elastic dislocation model
of subduction thrust locking. The residual deformation exhibits geometrically and geologically plausible characteristics and
is presumed to represent net geologic deformation of the upper plate that is independent of transient strain accumulation and
release in the subduction zone earthquake cycle. These results substantiate the hypothesis that part of the discrepancy
between crustal stress and geodetically measured strain rate directions stems from an inappropriate comparison of parameters
representing processes at different time-scales. In the particular case of central Japan, it appears that the
high-frequency, relatively low-magnitude strain rates associated with subduction zone locking do not greatly affect the
crustal stress field, whereas long-term horizontal motion between northeast and southwest Japan is more evident in the stress
field than in the geodetically measured total strain rate field. In other words, the state of crustal stress in central
Japan and the concentration of neotectonic deformation within the Japanese Alps are controlled by crustal collision and are
relatively insensitive to earthquake processes on the subduction thrusts beneath.
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8123 Dynamics: seismotectonics
DE: 8159 Rheology: crust and lithosphere (8031)
DE: 8163 Rheology and friction of fault zones (8034)
DE: 8164 Stresses: crust and lithosphere
SC: Tectonophysics [T]
MN: Fall Meeting 2005