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Zusammenfassung:
The Hikurangi Subduction Margin was the recent focus of two IODP expeditions seeking to explore the cause and effect of slow slip earthquake generation at this plate boundary. Characterising the stress field across the Hikurangi Subduction Margin is a crucial element of to understanding the relationship between the contemporary in-situ stress state, active and inactive structures along the subduction front, and fluid pressures and the observed spatial variation in subduction behaviour. Existing stress observations rely on earthquake focal mechanisms and limited onshore borehole data from industry wells on the overriding plate. Reported pore pressures within the over-riding plate are often close to vertical stress magnitudes at shallow depths. Variability of in-situ stress orientations occur along strike of the subduction trench, with a subduction trench parallel SHmax in the south transitioning to a plate motion parallel, trench-oblique SHmax further north. This spatially correlates with observed changes in subduction interface coupling and earthquake behaviour. Here we present new stress field orientation data acquired from resistivity image logging carried out in IODP Expedition 372 using the logging while drilling GeoVision Resistivity tool. We report Shmin orientations from borehole breakout observations of N-S at Site U1518 near the deformation front, and NW-SE from Site U1519 within the upper plate. These data represent the first estimates of stress field orientation (from drilling data) in the outer forarc, near the deformation front of the Hikurangi Margin, an area characterised by shallow slow slip.
