Stress gradient in arc–back arc regions and plate subduction

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Abstract
Trajectories of the maximum horizontal tectonic stress σHmax have been compiled for five regions of plate convergence, i.e., the Alaska‐Aleutian, central Europe, Hellenic‐Aegean, and southwest and northeast Japan. For southwest and northeast Japan, stress trajectories have been considered for both the present and Miocene times. The results indicate that in most cases a systematic stress gradient exists in the crust of the overlying plate: the stress is, from the plate boundary landward, compressional, shear, and tensional even in the region where active back arc spreading is not taking place. In some regions, σHmax maintains its direction subparallel with that of convergence as it changes from σ1 to σ2 (σ1>σ2>σ3) in the back arc, whereas in other regions, σHmax direction is changed to become parallel to the arc. Such a change appears to require some mechanisms in addition to simple landward stress attenuation. Some discussion is given on such mechanisms. None of the models proposed so far, however, seems to explain the observed extensional tectonics in back arc regions adequately.