RV Sindhu Sankalp CRUISE SSK 058 (17 th Dec 31 st Dec 2013)

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Theodore Thompson
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(Chennai-Chennai) NATIONAL INSTITUTE OF OCEANOGRAPHY

2 RV Sindhu Sankalp CRUISE SSK 058 (17 th Dec 31 st Dec 2013) REPORT ON CRUISE SSK-058 OF RV SINDHU SANKALP (Chennai-Chennai) NATIONAL INSTITUTE OF OCEANOGRAPHY (Council of Scientific and Industrial Research) Dona Paula, Goa ii

3 CONTENTS 1.0 Summary 2.0 Cruise track (Figure 1) 3.0 Itinerary 4.0 Participants 4.1 Scientific component 4.2 Ship s complement 5.0 Introduction 6.0 Objectives 7.0 Work done 7.1 Broadband OBS receivers 8.0 Performance of equipment used 9.0 Performance of the ship 10.0 Conclusion 11.0 Recommendations 12.0 Acknowledgements Annexure I (Table 1) 1

4 1.0 SUMMARY This is expedition onboard RV Sindhu Sankalp under GENIAS-Geodynamics and Earthquake generating processes in NE India and Andaman Subduction zone, project is a XII-plan CSIR Network program in which CSIR-NIO is a participating lab, the nodal lab is CSIR-NGRI. The objective of the cruise is to deploy 12 units of the Ocean Bottom Seismometer (OBS) units at pre-selected locations in the Andaman Sea. Locations of the deployment were selected based on the tectonic domains and the seismicity of the region during the past 5-year period. Andaman Back Arc Basin was formed as a consequence of the subduction of the Indian plate below the SE-Asian plate. Earlier studies carried out by NIO in this region have provided unmistakable evidence of the back-arc spreading center and also provided insights into the evolution of the Andaman back arc basin. During the XII th Plan period it is proposed to conduct a passive OBS experiment to understand the nature of crust beneath the Alcock and Sewell rise complexes. Crustal structure near the back arc spreading center, off-nicobar swarm region, the west Andaman Fault, and the Invisible bank regions. During the present cruise, 12 OBS units have been successfully deployed. These self recording broadband receiver units will be on the seafloor listening to the earthquakes that occur in the region. We plan to recover these units in the first/second week of May The present cruise has started from Chennai Port on 17 th December, 2013 and returned to Chennai on 31 st Dec

2.0 CRUISE TRACK Figure 1:Ocean Bottom Seismometer deployment location map. Numbered red circles with cross represent the locations of deployment. Star symbol denotes the historical earthquake events.

5 2.0 CRUISE TRACK Figure 1:Ocean Bottom Seismometer deployment location map. Numbered red circles with cross represent the locations of deployment. Star symbol denotes the historical earthquake events. Square white symbols over the islands represent land stations which are part of ISLANDS network (Srijayanthi et al., 2012). 3.0 ITINERARY Chennai to Chennai Departure: 17 Dec Arrival : 31 Dec

6 4.0 PARTICIPANTS 4.1 Scientific component Sr.No Id No Name Designation Dr. K.A. Kamesh Raju Chief Scientist - Chief of Expedition Dr. Pawan Dewangan Scientist Mr. T. Ramesh TA Mr. Buddhadas Patole TA Mr. Muhammad Shuhail Junior Research Fellow Mr. Pabitra Singha Project Assistant Mr. Rahul Mavi Project Assistant 8. Mr. Arne SCHWENK OBS Technician 9. Mr. Thanil Thentran Deck Hand 10. Mr. Agnello Deck Hand 4.2 Ship s complement S-No Crew Member s Name Rank 1 Capt.K.T.Jaidip Master 2 Alwyn Gray Stephen Ch. Officer 3 P.Kaliamurthi 2nd Officer 4 Ravitia Gowtham Ch. Engineer 5 Palanivel Rajaraman 2nd Engineer 6 Vikas Olayil 3rd Engineer 7 Bagavathy Subramanian El. Officer 8 Viswanathan Gowthaman A/B 9 Rajbhar Ramjit A/B 10 M. Jeya Britto OS 11 Tiwari Rajat Oiler 12 Bose Hemanathan ERR II 13 Sathya Prakash Cook 14 Riyaz Ahmad GS 15 Karukola Simhachlam SUPERNUMERARY 16 G. Silambarasan SUPERNUMERARY 4

7 5.0 INTRODUCTION The Andaman back arc basin has been studied in detail by CSIR-NIO. The recent evolutionary history of the back arc basin (Kamesh Raju et al., 2004) and studies on the structural controls on the mega-thrust earthquakes (Kamesh Raju et al., 2007) and the submarine arc volcanism (Kamesh Raju et al., 2012) have enhanced our understanding of the Andaman Back arc basin. It has been proposed to conduct a passive OBS experiment to understand the nature of the crust beneath the back arc basin and the nature of the spreading center. The present cruise is a part of this initiative. The objective of the present cruise is to deploy the OBS units at selected locations. Variuos tectonic domains such as the back arc spreading center, Alcock and Sewell seamounts, west Andaman Fault, Off Nicobar region, and the invisible bank region have been chosen for the deployment of OBS units. Multibeam bathymetry data is available for most of these locations. 6.0 OBJECTIVES To deploy the broadband Ocean Bottom Seismometers to initiate the passive OBS experiment. 7.0 WORK DONE During this expedition, 12 broadband OBS units have been deployed at pre-selected locations (Figure 1). The OBS units have been hired from K.U.M. Umwelt- und Meerestechnik, Kiel GmbH, Kiel, Germany. Pressure floats mounted on titanic frame, hydrophone, acoustic release, three-component seismometer unit and the anchor weight frame are the main components of the OBS unit (Figure 2). The work involved testing of the acoustic releases, preparation of seismometer units, calibration of the clocks, setting the initial parameters, assembling the OBS units and their deployment. Out of the 12 units six were deployed from the fore-deck section using the hydrographic winch and the J-frame and the remaining six were deployed from the aft-deck using the A-frame and the deep-sea winch. OBS deployment locations and the tectonic setup of the deployment region is provided in Table Broadband OBS receivers The main objectives of the cruise are to deploy the OBS units at pre-selected locations. Figure 2 shows the picture of an assembled OBS and the deployment procedure followed in the cruise. These units are also nick named as LOBSTER (Longterm OBS for Tsunami and Earthquake Research). These units are rated for operation up to 6000 m water depth. 5

8 The LOBSTER is equipped with a broadband three component seismometer. The frequency band width ranges from 60 secs to 100 Hz, a hydrophone with same frequency range, a digital seismic recorder with 4 x 24 bit input, an acoustic release and several relocation aids like flag, flash and radio beacon. The buoyancy is made from syntactic foam for enhanced reliability and robustness of the system. For the same reason, complete frame and pressure tubes are made from titanium. The careful design of the system led to a total recovery rate of better than 96% in the past years. Dynamic range of both seismometer and digitizer is about 130dB, the total power consumption is as low as 620 mwatt only. During the cruise, a dedicated calibrated GPS was installed to synchronize the digitizer, the units were tested thoroughly in the lab before assembly and deployment. LOBSTERs have been deployed roughly 12 hours each. Due to the limited deck space onboard RV Sindhu Sankalp, we deployed 6 units from the fore deck and six units from the aft-deck area. Figure 2: OBS deployment onboard RV Sindhu Sankalp, Cruise ssk-058. a) assembled OBS unit, b-d) deployment steps. 6

9 8.0 PERFORMANCE OF EQUIPMENTS USED During the entire cruise, multi-beam bathymetry (MB) and the sub-bottom profiler were used. Both the instruments performed well. The swath coverage of the MB-system was is still a concern. 9.0 PERFORMANCE OF THE SHIP Overall the ship s performance was satisfactory. The major concern however, is the average speed of the vessel. She was making 7 to 7.5 knots on an average. In favorable weather conditions the speed is going up to 8.5 knots. This needs improvement. An average of 10 knots speed during the transit time would be ideal. The speed becomes more critical if there is large transit involved, as was the case during SSK058. It took 5 days to reach Andaman Sea from Chennai, in moderate sea conditions CONCLUSION This is the first ever passive OBS experiment in the Andaman Sea region. We had issues with the customs clearance at Chennai, there were inordinate delays from the agents side. It appeared that there was no coordination among the team that was responsible for clearing the consignment. Due to the efficient and helpful crew, we could manage to deploy the 12 OBS units within six days of ship-time. This cruise to the Andaman Back-arc basin was undertaken for CSIR Network project, GENIAS of CSIR- NGRI and CSIR-NIO RECOMMENDATIONS The facility onboard is a great relief. It is working well, making communications a lot easier. Thanks to the ship-cell team for installing this long awaited facility. Slow transit speed of the vsl has been a major concern in this cruise. The average speed varied from 7 to 7.5. Fouling of hull with bio-growth was pointed as one of the reasons. Cleaning may help improve speed by about 1 knot. We hope the MB system swath coverage issue will be resolved soon and we get good coverage in future cruises. 7

10 Captain, Officers and crew have been extremely cooperative and helpful. Deployments have been very smooth and quick. The German OBS technician is cooperative and systematic. Ship cell technicians Mr. T. Ramesh and Mr. Buddhadas Patole have provided excellent support. The cook is excellent, catering and other amenities are satisfactory. In all a successful cruise marking the initiation of a first ever Passive OBS experiment in the Andaman Sea region. Results are expected to provide better insights into the nature of the crust and fault structures. The studies would lead to better understanding of the earthquake generating processes and the geodynamics of the region ACKNOWLEDGEMENTS We acknowledge the support and co-operation from the Master and crew members of the RV Sindhu Sankalp during the expedition. Mr. Ramesh T. and Mr. Buddhadas Patole, of the ship-cell, CSIR-NIO, have provided excellent support. We thank Dr. S.W.A. Naqvi, Director CSIR-NIO for providing ship-time, encouragement and support. 8

11 13.0 Annexure I Table 1. OBS deployment locations Date/ Time GMT OBS Lat (N) Lon (E) Depth (m) Tectonic setup OBS1 07º ' 91º ' 3900 Subduction zone (south) proximal to 90E Ridge OBS2 07º ' 94º ' 1832 Volcanic arc Off Nicobar Is. OBS3 08º ' 93º ' 4183 WAF west of Sewell rise OBS4 09º ' 94º ' 1681 Sewell Rise OBS5 09º º ' 1996 Sewell Rise OBS6 10º º20,0789' 3440 ABSC - seg B OBS7 10º º ' 3617 ABSC - seg C OBS8 12º º ' 1080 Alcock Rise OBS9 11º º ' 2266 Alcock Rise near to Barren Is. OBS10 10º º Invisible Bank OBS11 09º º Between A and N OBS12 10º º Subduction zone (north) 9

Short Cruise Report. RV MARIA S. MERIAN Cruise MSM15/5

Short Cruise Report. RV MARIA S. MERIAN Cruise MSM15/5 Ingo Grevemeyer Leibniz Institut für Meereswissenschaften IFM-GEOMAR Abt. Marine Geodynamik Wischhofstraße 1-3 D-24148 Kiel Tel: +49 431 600 2336 Fax: +49 431 600 2922 Email: igrevemeyer@ifm-geomar.de