Wallace LM, TAN1907 Science Party. 2021. Hikurangi Ocean Bottom Investigation of Tremor and Slow Slip (HOBITSS VI, TAN1907). Lower Hutt (NZ): GNS Science. 180 p. (GNS Science report; 2020/09). doi:10.21420/DC55-GM55.
Abstract
HOBITSS VI was a 12-day (29 October – 9 November 2019) Wellington to Wellington R/V Tangaroa voyage (TAN1907). Objectives of TAN1907 were to undertake seafloor geodetic and seismic instrument deployments, recoveries and surveys offshore of the Gisborne, Hawke’s Bay and Wairarapa coasts. 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 (SSEs), as well as to deploy a Wave Glider to survey two precision transponder arrays to monitor cm-level horizontal tectonic movements of the seafloor (using GPS-Acoustic techniques) near the Hikurangi Trench. We also recovered an existing seafloor transponder array offshore of Gisborne that was deployed in 2015. Ocean bottom seismometers (OBS) were recovered, and these data will be used to compare the generation of ‘fast-slip’ earthquakes with slow-slip earthquakes and will complement data coming from the BPRs and monitoring instruments installed in International Ocean Discovery Program boreholes offshore of Gisborne. Next generation seafloor instruments (developed by Lamont-Doherty Earth Observatory [LDEO]) that combine pressure and seismic sensors (POBS) were also recovered. The offshore Gisborne to Hawke’s Bay region was targeted due to the large and frequent SSEs that occur there. Offshore Wairarapa and Hawke’s Bay have been targeted for GPS-Acoustic array deployments to determine the degree of locking near the Hikurangi Trench, which is currently not constrained.
Five BPRs belonging to Kyoto University, three BPRs and three POBS belonging to LDEO and six BPRs belonging to the University of Texas (UTIG) and GNS Science (GNS) were retrieved during the voyage. We unfortunately were unable to retrieve three additional BPRs belonging to UTIG/GNS and two BPRs belonging to LDEO; we were unable to establish communication with them, and the reasons for this are currently unknown. Five OBS belonging to the Earthquake Research Institute, University of Tokyo (ERI) were also retrieved. A Wave Glider was deployed off the Wairarapa coast at the beginning of the voyage to survey in two GPS Acoustic transponder arrays (consisting of three precision transponders per array). In all, 14 BPRs, five OBS, three POBS (with pressure and OBS) and three precision transponders were recovered (25 instrument recoveries). Most of these instruments were originally deployed in late 2018, on TAN1809, and in early 2019 with the R/V Roger Revelle (RR1903). Five BPRs belonging to Kyoto University were also deployed during the voyage. All voyage objectives underpin research funded by a Ministry for Business, Innovation & Employment Endeavour Fund programme: ‘Diagnosing peril posed by the Hikurangi subduction zone: New Zealand’s largest plate boundary fault’ (Contract C05X1605). (auth)
