R/V Sonne SO215 Cruise Report The Louisville Ridge – Tonga Trench collision: Implications for subduction zone dynamics 25th April – 11th June 2011 Auckland (New Zealand) – Townsville (Australia) R/V Sonne SO215 Cruise Report The Louisville Ridge – Tonga Trench collision: Implications for subduction zone dynamics 25th April – 11th June 2011 Auckland, New Zealand – Townsville, Australia Chief Scientist Co-Chief Scientist Professor Christine Peirce Professor Anthony Watts Department of Earth Sciences Department of Earth Sciences Durham University University of Oxford South Road South Parks Road Durham Oxford DH1 3LE OX1 3LE [email protected] [email protected] October 2011 Table of Contents Summary.......................................................................................................................5 1 Background and cruise objectives...........................................................................5 1.1 Introduction ....................................................................................................................................5 1.2 Dynamics........................................................................................................................................6 1.3 Scientific objectives and key hypotheses to be tested ....................................................................7 1.4 Acquisition plan..............................................................................................................................8 2 Territorial waters and diplomatic clearances ........................................................9 3 Mobilisation...............................................................................................................9 4 Work conducted and data collected ......................................................................10 5.1 Seismic profiles ............................................................................................................................11 5.1.1 Seismic source .......................................................................................................................11 5.1.2 Multichannel streamer...........................................................................................................16 5.1.3 Ocean-bottom seismographs .................................................................................................18 5.1.4 Shot timing.............................................................................................................................19 5.1.5 Profile overview.....................................................................................................................19 5.2 Gravity..........................................................................................................................................34 5.3 Magnetics......................................................................................................................................37 5.4 Swath bathymetry .........................................................................................................................38 5.5 Sub-bottom profiling ....................................................................................................................40 5.6 Navigation ....................................................................................................................................40 5.7 Expendable bathymetric thermographs ........................................................................................40 5.8 Sound velocity profiling ...............................................................................................................41 5.9 Monowei volcanic centre..............................................................................................................43 6 Cruise narrative ......................................................................................................46 7 Equipment performance ........................................................................................55 7.1 Seismic equipment........................................................................................................................55 7.2 Onboard data quality control and processing ...............................................................................56 7.3 Ocean-bottom seismographs.........................................................................................................56 7.4 Gravity..........................................................................................................................................56 7.5 Magnetics......................................................................................................................................56 7.6 Ship’s machinery and fitted equipment ........................................................................................57 7.7 Swath bathymetry .........................................................................................................................57 7.8 Sub-bottom profiling ....................................................................................................................57 7.9 XBT and SVP ...............................................................................................................................57 7.10 Navigation and underway track plotting.....................................................................................57 8 Weather....................................................................................................................57 9 Demobilisation.........................................................................................................58 10 Achievements.........................................................................................................58 Acknowledgements ....................................................................................................58 References...................................................................................................................59 Tables ..........................................................................................................................60 Table 1 – Scientific and technical personnel ......................................................................................60 Table 2 – OBS deployment locations – Line A ..................................................................................62 Table 3 – OBS deployment locations – Line B ..................................................................................63 Table 4 – OBS deployment locations – Line C ..................................................................................64 Table 5 – OBS deployment locations – Line G ..................................................................................66 Table 6 – Multichannel seismic profile locations vs. FFID numbers .................................................66 Table 7 – Multichannel seismic acquisition configuration .................................................................67 Table 8 – Gravity base station locations.............................................................................................68 Table 9 – Marine vs. land gravimeter readings ..................................................................................69 Table 10 – Sound velocity profile location.........................................................................................70 Table 11 – Expendable bathymetric thermograph deployment locations...........................................71 Table 12 – Cruise way points .............................................................................................................71 Transit from Auckland way points..................................................................................................71 Seismic profile ends way points......................................................................................................71 _______________________________________________________________________________________________ RV Sonne Cruise 215 Cruise Report October 2011 3 OBS deployment and recovery way points .....................................................................................72 Line A 72 Line B 72 Line C 73 Line G 74 Swath survey way points.................................................................................................................75 Phase 1 – transit from Profile A to Profile C 75 Phase 2 – Monowei volcanic centre – eruption 75 Phase 3 – Monowei volcanic centre – post-eruption 75 Phase 4 – infilling of forearc regional coverage 76 Phase 5 – transit to Townsville 76 Sea state for much of the cruise! _______________________________________________________________________________________________ RV Sonne Cruise 215 Cruise Report October 2011 4 Summary We conducted a marine geophysical survey of the Louisville Ridge intersection with the Tonga Trench subduction system onboard R/V Sonne (SO215) during April-June 2011. The data are of high-quality and include multichannel seismic reflection and refraction, gravity and magnetic, swath bathymetry and sub- seabed imaging profiles of the crustal structure of the Louisville Ridge, and the pre- and post-subduction crust of both the down-going and over-riding plates. We were also able to acquire an additional seismic profile trench-parallel in the forearc, undertake a number of instrumentation trials for the NERC’s Ocean- Bottom