The state of stress in the shallow crust of the Hikurangi Subduction Margin hangingwall, New Zealand

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Title: The state of stress in the shallow crust of the Hikurangi Subduction Margin hangingwall, New Zealand
Authors: Behboudi, EffatMcNamara, DavidLokmer, IvanWallace, LauraManzocchi, Tom
Permanent link: http://hdl.handle.net/10197/12472
Date: 30-Apr-2021
Online since: 2021-09-14T11:12:43Z
Abstract: Knowledge of in situ stress fields is critical for a better understanding of deformation, faulting regime, and earthquake processes in seismically active margins such as the Hikurangi Subduction Margin (HSM), North Island, New Zealand. In this study, we utilize Leak-off Test (LOTs) data, borehole breakout widths measured from borehole image logs, and rock unconfined compressive strengths (UCS) derived from empirical P-wave velocity log relationships to estimate vertical (Sv), minimum (Shmin), and maximum horizontal stress magnitudes (SHmax) and interpret the likely faulting regime experienced in four boreholes (Kauhauroa-2, Kauhauroa-5, Titihaoa-1, and Tawatawa-1). Using the standard Anderson’s stress regime classification, relative stress magnitudes in Kauhauroa-5 at 1200-1700 m depth and Kauhauroa-2 at 1800-2100 m and indicate that the stress state in the shallow crust of the central and northern part of HSM is predominantly strike-slip (SHmax≥Sv≥Shmin) and normal Sv≥SHmax> Shmin respectively. Moving to the offshore, southern HSM a dominant compressional stress regime (SHmax> Shmin >Sv), with some possible strike slip stress states are observed in Titihaoa-1 from 2240-2660 m and Tawatawa-1 from 750-1350 m. The observed normal/strike-slip stress state in Kauhauroa-2 and Kauhauroa-5 is consistent with the average SHmax orientation of 64° ± 18° (NE-SW) determined from borehole breakouts and dominantly NE–SW striking normal faults interpreted from seismic reflection data. The normal/ strike-slip regime in this area suggests that the stress regime here is probably influenced by the effect of the clockwise rotation of the HSM hangingwall associated with oblique Pacific-Australia plate convergence (ENE-WSW). Alternatively, these stress states could be the result of gravitational collapse due to rapid uplift of the subducting plate during the mid-Miocene. The compressional stress regime in the southern HSM in Titihaoa-1 and Tawatawa-1 is in agreement with the SHmax orientations of 148° ± 14° (NW-SE ) and 102° ± 16° (WNW-ESE) obtained from image logs and mapped NE–SW striking reverse faults in this region. This observation suggests that the tectonics here are strongly linked to the subduction of Hikurangi plateau under Australian Plate (NW-SE) or active frontal thrusts in the overriding plate.
Funding Details: Science Foundation Ireland
Funding Details: Geological Survey of Ireland (GSI)
Type of material: Conference Publication
Publisher: Copernicus GmbH
Copyright (published version): 2021 the Authors
Keywords: In situ stress fieldsEarthquake processesBorehole image logsVelocity logs
DOI: 10.5194/egusphere-egu21-10217
Other versions: https://www.egu21.eu/
Language: en
Status of Item: Peer reviewed
Conference Details: The EGU General Assembly 2021 (EGU21), Virtual Conference, 19-30 April 2021
This item is made available under a Creative Commons License: https://creativecommons.org/licenses/by/3.0/ie/
Appears in Collections:Earth Sciences Research Collection
ICRAG Research Collection

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