Electrical resistivity imaging of the inter-plate coupling transition at the Hikurangi subduction margin, New Zealand

Heise, Wiebke; Ogawa, Yasuo; Bertrand, E. A.; Caldwell, T. G.; Yoshimura, Ryokei; Ichihara, Hiroshi; Bennie, S. L.; Seki, Kaori; Saito, Zenshiro; Matsunaga, Yasuo; Suzuki, Atsushi; Kishita, Takahiro; Kinoshita, Yusuke

doi:10.1016/j.epsl.2019.115710

Cited by 13 publications

(7 citation statements)

References 43 publications

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“…Slip on these shallow reverse faults may rotate the S Hmax into the observed NW‐SE orientations recorded from borehole data here, while the overall subduction S Hmax at depth remains in a NE‐SW orientation driven by relative plate motion. High fluid pressure can also encourage slip on deeper faults, although in the southern HSM, magnetotelluric data (Heise et al., 2019), seismic tomography studies (Bassett et al., 2014; Eberhart‐Phillips et al., 2017), and borehole analysis (except for offshore boreholes Titiahoa‐1 and Tawatawa‐1; Burgreen‐Chan et al., 2016; Darby & Funnell, 2001) do not provide evidence for elevated fluid content or pressure.…”

Section: Discussionmentioning

confidence: 99%

Spatial Variation of Shallow Stress Orientation Along the Hikurangi Subduction Margin: Insights From In‐Situ Borehole Image Logging

et al. 2022

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Knowledge of the contemporary in‐situ stress orientations in the Earth's crust can improve our understanding of active crustal deformation, geodynamic processes, and seismicity in tectonically active regions such as the Hikurangi Subduction Margin (HSM), New Zealand. The HSM subduction interface is characterized by varying slip behavior along strike, which may be a manifestation of combined variations in both stress state and the mechanical properties of faults and their hanging walls. Alternatively, these variations in subduction thrust slip behavior may drive heterogeneity in the stress state in space and time. In this study, we analyze borehole image and oriented four‐arm caliper logs acquired from 13 boreholes along the HSM to present a comprehensive stress orientation data set from borehole data within the shallow (<3 km) upper plate of the subduction thrust. Our results reveal a 065°/245° SHmax orientation within the central HSM (Hawke's Bay region) which rotates to 112°/292° and 140°/320° in the southern HSM. This rotation of SHmax orientation correlates spatially with along‐strike variations in subduction interface slip behavior, characterized by creep and/or shallow episodic slip events in the central HSM and interseismic locking in the south. The borehole SHmax orientations suggest that contemporary stress orientations may be caused in part by along‐strike variation in deformation style imposed by clockwise rotation of forearc. In the southern HSM, borehole‐derived SHmax orientations are inconsistent with SHmax orientations derived from focal mechanism solutions in the subducting plate, implying some degree of mechanical decoupling between the shallow hanging wall and subducting slab.

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Section: Discussionmentioning

confidence: 99%

Spatial Variation of Shallow Stress Orientation Along the Hikurangi Subduction Margin: Insights From In‐Situ Borehole Image Logging

et al. 2022

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“…The northern and central HSM have high Pp based on borehole data (Burgreen-Chan et al, 2016;D. Darby & Funnell, 2001), magnetotellurics (Heise et al, 2019), and seismic tomography (Bassett et al, 2014;Eberhart-Phillips et al, 2017). Overpressure reduces the effective normal stress on fault planes, meaning that the existing NNE/NE striking faults in this region will be able to slip at lower shear stresses.…”

Section: Shallow Hsm Tectonicsmentioning

confidence: 99%

Shallow Tectonic Stress Magnitudes at the Hikurangi Subduction Margin, New Zealand

Behboudi¹,

McNamara

Lokmer

2022

Preprint

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Quantifying tectonic stress magnitudes is crucial in understanding crustal deformation processes, fault geomechanics, and variable plate interface slip behaviors in subduction zones. The Hikurangi Subduction Margin (HSM), New Zealand is characterized by along-strike variation in interface slip behavior, which may be linked to tectonic stress variations within the overriding plate. This study constrains in-situ stress magnitudes of the shallow (<3km) overriding plate of the HSM to better understand its tectonics and how they relate to larger scale subduction dynamics. Results reveal σ3: Sv ratios of 0.6-1 at depths above 650-700 m TVD and 0.92-1 below this depth interval along the HSM and SHmax: Sv ratios of 0.95-1.81 in the central HSM, and 0.95-3.12 in the southern HSM. These stress ratios suggest a prevalent thrust to strike-slip (σ1=SHmax) faulting regime across the central and southern HSM. In the central HSM, the presence of NNE-NE striking reverse faults co-existing with a modern σ1 aligned ENE-WSW (SHmax) suggests that overtime the stress state here evolved from a contractional to a strike-slip state, where the compressional direction changes from perpendicular (NW-SE) to subparallel (ENE-WSW) to the Hikurangi margin. This temporal change in stress state may be explained by forearc rotation, likely combined with development of upper plate overpressures. In the southern HSM, the modern WNW-ESE/ NW-SE σ1 (SHmax) and pre-existing NNE-NE striking reverse faults indicate that stress state remains contractional and subparallel (NW-SE) to the Hikurangi margin overtime. This may reflect the interseismic locked nature of the plate interface.

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“…The phase tensor ϕ is generally represented as an ellipse, and the orientation of the principal axes of the ellipse indicates electrical conductivity variations and gradients. It is an indicator of the dimensionality and directionality of the electrical conductivity structures within the subsurface (Caldwell et al, 2004), but can also be used to make preliminary assessments on the overlying resistivity distribution (Heise et al, 2019). Two invariants of the phase tensor ϕ are commonly used to infer the dimensionality of the subsurface, the phase tensor skew angle β and the phase tensor ellipticity λ. β defines the phase tensor asymmetry and indicates the presence of 3D structures.…”

Section: Magnetotelluric Datamentioning

confidence: 99%

Probabilistic Cover‐Basement Interface Map in Cloncurry, Australia, Using Magnetotelluric Soundings

et al. 2021

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A great interest has been shown by the Australian geoscience community to define the depth to crystalline basement. With the Australian continent being covered by sedimentary sequences in 80% of its surface (e.g., Kennett et al., 2019), the characterization of the cover-basement interface is essential to mineral, energy, and groundwater exploration. Drilling provides the most reliable source of information to estimate the depth to basement and gives first-order information on the nature of the geological formations, in terms of lithology and petrophysics. However, drilling dataset can have an irregular and/or sparse coverage, generally biased toward certain types of geology according to past exploration strategies. Geophysics, by contrast, is generally regularly sampled, covers wide areas and provide continuous images of the subsurface, making it less influenced by sampling bias. Its limitation is that it has less resolution and the models derived through inversion are non-unique and interpretations are subject to ambiguity.The contact between the unweathered basement and cover sequences often presents a clear contrast in the petrophysical properties of the rocks, in particular for the electrical conductivity, or its inverse, the electrical

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Electrical resistivity imaging of the inter-plate coupling transition at the Hikurangi subduction margin, New Zealand

Cited by 13 publications

References 43 publications

Spatial Variation of Shallow Stress Orientation Along the Hikurangi Subduction Margin: Insights From In‐Situ Borehole Image Logging

Spatial Variation of Shallow Stress Orientation Along the Hikurangi Subduction Margin: Insights From In‐Situ Borehole Image Logging

Shallow Tectonic Stress Magnitudes at the Hikurangi Subduction Margin, New Zealand

Probabilistic Cover‐Basement Interface Map in Cloncurry, Australia, Using Magnetotelluric Soundings

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