Hikurangi Ocean Bottom Investigation of Tremor and Slow Slip (HOBITTS IV)

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Wallace LM, TAN1705 Science Party. 2019. Hikurangi Ocean Bottom Investigation of Tremor and Slow Slip (HOBITTS IV). Lower Hutt (NZ): GNS Science. 28 p. + appendices. (GNS Science report; 2017/40). doi:10.21420/G2DG92.

HOBITSS IV was a 12-day (24 June–5 July 2017) Wellington to Wellington R/V Tangaroa voyage (TAN1705). Objectives of TAN1705 were to (1) undertake seafloor geodetic instrument deployments, recoveries, and surveys offshore Gisborne and Mahia, and (2) acquire multicores along the Hikurangi margin and offshore the north-eastern South Island to evaluate the extent of turbidite deposition following the November 2016 Kaikōura earthquake. The seafloor geodetic aims involve using Bottom Pressure Recorders (BPRs) to determine the cm level vertical movement (upward or downward) of the seafloor during slow slip events, as well as to survey an existing seafloor transponder array using GPS-Acoustic methods to track cm level horizontal tectonic motion of the seafloor. The offshore Gisborne and Mahia region are targeted due to the large and frequent slow slip events that occur there. 5 Bottom Pressure Recorders (BPRs) belonging to Tohoku University were recovered during the voyage. These BPRs were deployed in June 2016 (on TAN1607), and recorded data for one year. 5 BPRs belonging to Kyoto University, and 4 BPRs belonging to the University of Texas were deployed on the voyage (for a total of 9 deployments); these will be retrieved on a voyage planned for later in 2018. A GPS-A survey of a transponder array offshore Gisborne was undertaken for 30 hours, which will result in a position for the array accurate to within a few cm. The second phase of the voyage (commencing July 30th) involved multicore sample acquisition at 26 sites, spanning from offshore Hawke Bay to Pegasus Bay. The multicoring builds on results from an earlier piston coring and multicoring campaign1 November 2016 that was interrupted by the Kaikōura earthquake. All voyage objectives underpin research funded by an MBIE Endeavour fund programme: “Diagnosing peril posed by the Hikurangi subduction zone: New Zealand’s largest plate boundary fault.” (auth)