[S-CG43] Shallow and intermediate depth intraslab earthquakes: seismogenesis and rheology of the slab

[SCG43-02] Slab Seismicity Demonstrates Varied Initial Hydration and within-slab Fluid Migration

*Donna Eberhart-Phillips^1,2, Stephen Bannister³, Martin Reyners³ (1.GNS Science, Dunedin, 2.Univ. California Davis, 3.GNS Science, Lower Hutt)

Keywords:Subduction, Seismicity, Hydration

The slab earthquakes are enabled by embrittlement due to overpressure from accumulated water of dehydration, which can migrate across the slab or along dip depending on pressure gradients and fracture permeability. Zones of abundant slab seismicity may indicate areas with more dehydration or areas of more fluid accumulation. Earthquake rupture also enhances fracture permeability and coseismic fluid flux. Dense slab seismicity may thus relate to prominent slab fluid release into the mantle. Subducted slabs that have spatially varied seismicity demonstrate heterogeneous initial hydration in the outer rise yielding zone, with greater hydration for slower segments or thicker or more fractured slab. In New Zealand, dense seismicity is related to subduction of an edge of Hikurangi Plateau, which would have resisted subduction forming a broad region of excess fracturing and hydration. In Vanuatu, subduction of a highly fractured ridge system forms a zone of slab seismicity. In the Lesser Antilles, subducted fracture zones have enhanced hydration and dehydration. The Hikurangi dense seismicity relates to high slab fluid release, where distinctive low Qs underlies the massive rhyolitic volcanism in the central Taupo Volcanic Zone. The numerous earthquakes occurring across the slab imply migration of water and embrittlement of the cooler slab core, and allow rapid release of water into the mantle wedge. Rapidly rising melt may also facilitate additional underlying slab fluid flux through fractures and seismicity. This symbiotic relationship may thus promote localization of water release.