Non-volcanic tremor and discontinuous slab dehydration

Non‐volcanic tremor is a recently discovered fault slip style occurring with remarkable regularity in space near the down‐dip end of the locked zone on several subduction thrust interfaces. The physical mechanisms and the controls on the location of tremor have not yet been determined. We calculate the stable mineral assemblages and their water content in the subducting slab, and find that slab dehydration is not continuous, but rather restricted to a few reactions localised in pressure‐temperature space. Along geothermal gradients applicable to Shikoku and Cascadia ‐ where tremor has been relatively easy to detect ‐ tremor locations correlate with discontinuous and localised voluminous water release from the breakdown of lawsonite and chlorite + glaucophane respectively. The shape of the pressure‐temperature path for subducting slabs prevents fluid release at depths above and below where these dehydration reactions occur. We conclude that abundant tremor activity requires metamorphic conditions where localised dehydration occurs during subduction, and this may explain why tremor appears more abundant in some subduction zones than others. Key Points Discontinuous dehydration is localised to some points on the subduction P‐T path Abundant tremor activity correlates with localised voluminous water release Significant tremor activity requires specific metamorphic conditions