Stress orientations in subduction zones and the strength of subduction megathrust faults

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Science  11 Sep 2015:
Vol. 349, Issue 6253, pp. 1213-1216
DOI: 10.1126/science.aac5625

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Faults well oriented for failure

A deck of cards will remain motionless while pressed on from above, but easily separates when sheared. Similarly, the ease by which geological faults rupture depends on the geometry of the fault relative to the size and direction of stress. Hardebeck finds that faults are well oriented for failure in subduction zones worldwide, suggesting a low-stress environment (see the Perspective by Bürgmann). Subduction zone faults unleash powerful earthquakes. These estimates on the state of stress constrain potential generation mechanisms of destructive subduction zone earthquakes.

Science, this issue p. 1213; see also p. 1162


Subduction zone megathrust faults produce most of the world’s largest earthquakes. Although the physical properties of these faults are difficult to observe directly, their frictional strength can be estimated indirectly by constraining the orientations of the stresses that act on them. A global investigation of stress orientations in subduction zones finds that the maximum compressive stress axis plunges systematically trenchward, consistently making an angle of 45° to 60° with respect to the subduction megathrust fault. These angles indicate that the megathrust fault is not substantially weaker than its surroundings. Together with several other lines of evidence, this implies that subduction zone megathrusts are weak faults in a low-stress environment. The deforming outer accretionary wedge may decouple the stress state along the megathrust from the constraints of the free surface.

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