Dan Sandiford , Louis N. Moresi , Mike Sandiford, Rebecca Farrington, Ting Yang

Earthquake moment tensors in east Pacific (ePac) slabs typically show downdip tensional axes (DT), whereas in the west Pacific (wPac) they typically show downdip compressional axes (DC) or have mixed orientations indicative of unbending. Prevailing conceptual models emphasise uniform stress/deformation modes, i.e. bulk stretching or shortening, as the dominant control on intermediate depth seismic expression. In contrast we propose that much of the diversity in seismic expression is consistent with expectations of flexural strain accumulation due to systemic differences in slab geometry. Our analysis reveals two largely unrecognised features of ePac intraslab seismicity. Firstly, earth-quake clusters consistent with slab unbending are present in ePac slabs, albeit at much shallower depths than typical of wPac slabs. Secondly, intermediate depth ePac DT seismicity is strongly localised to the upper half of zones undergoing curvature increase, such as flat slab segments. Our study highlights how the seismic expression of slab flexure is impacted by the relative contribution of brittle and ductile deformation. The strongly asymmetric temperature structure that is preserved in sinking slabs means that seismicity disproportionately records the deformation regime in the colder part of the slab, above the neutral plane of bending. The expression of in-plane stress may be discernible in terms of a systematic modifying effect on the seismic expression of flexure.