KR09-08 Cruise: Walkaway VSP shooting in the Nankai Trough off Kumano

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1 Preliminary Report on KR09-08 Cruise: Walkaway VSP shooting in the Nankai Trough off Kumano July 19 July 25, 2009 Yokosuka - Shingu Masataka Kinoshita (IFREE-JAMSTEC) KR09-08 Shipboard Science Party

2 Acknowledgments Cost for air-gun operation by NME was supported by IFREE/JAMSTEC. VSP operation cost was shared by CDEX, IODP-MI and IFREE. CDEX provided us with great support on adjusting Chikyu and Kairei schedule. Dr. Kaneda and Dr. Kodaira were generous enough to shorten their shiptime after our VSO cruise. We are grateful to NanTroSEIZE PMT members, who agreed on carrying out our VSP experiment. The science party would acknowledge that the KR9-08 cruise involved very difficult operations which were only made possible by the professional skill of the following persons: Captain Mr. Susami, Chief Officer Mr. Kimura and KAIREI marine crew for overall support, including ship navigation, air-gun launching/recovery operation, and ship s life. JAMSTEC Marine Operation Department for cruise logistics. We also than technicians of Nippon Marine Enterprize, Co. Ltd. for their smooth air-gun operation.

3 Table of Contents KR09-08 Shipboard Science Party Abstract 1. Introduction 2. Explanatory Notes 3. Broadband seismic observation at the seafloor 4. Deployment of ocean-bottom seismometers 5. Walkaway VSP 5-1. Dummy run test 5-2. Source signal acquisition by Kairei hydrophone 5-3. Walkaway VSP

4 KR09-08 Shipboard Science Party Masataka Kinoshita: Chief Scientist IFREE/JAMSTEC Ryota Hino: VSP PI Tohoku University Yoshihiro Ito Tohoku University Nathan Bangs Institute for Geophysics University of Texas at Austin Hiroko Sugioka IFREE/JAMSTEC Tetsuo No IFREE/JAMSTEC

Abstract The KR09-08 cruise using JAMSTEC R/V KAIREI was conducted from July 19 to July 25, 2009, as a two-ship walkaway VSP (Vertical Seismic Profiling) experiment around the IODP NanTroSEIZE

5 Abstract The KR09-08 cruise using JAMSTEC R/V KAIREI was conducted from July 19 to July 25, 2009, as a two-ship walkaway VSP (Vertical Seismic Profiling) experiment around the IODP NanTroSEIZE drillsite C0009 (proposed site NT2-11B). The Deep Sea Drilling Vessel Chikyu kept her position at the site and is carrying out her riser drilling at Site C0009. While the seismometer array is set in place within the hole by Chikyu and 8 OBSs were distributed around Site C0009, Kairei keeps shooting her air-gun array and walked in & away. The walkaway VSP operation was carried out from 20:14 of July 24 to 11am of July 25, A quick-look achievement of the W-VSP is as follows: *NS line walkaway VSP, 25km south to ~30 km north with 60 m interval *Circle shooting VSP, 3.5 km radius And they were acheved in less than 15 hours.

6 1. Introduction The KR09-08 cruise using JAMSTEC R/V KAIREI was planned as a two-ship walkaway VSP (Vertical Seismic Profiling) experiment (Fig. 1) around the IODP NanTroSEIZE drillsite C0009. The Deep Sea Drilling Vessel Chikyu kept her position at the site and is carrying out her riser drilling at Site C0009 (proposed site NT2-11B; Fig. 2). While the seismometer array is set in place within the hole by Chikyu, Kairei keeps shooting her air-gun array and walk away. Scientific Objectives This experiment was designed as a part of IODP NanTroSEIZE project. The objectives of this experiment is to clarify geometry and properties along the locked portion of seismogenic fault zone below Site C0009, where M>8 great earthquakes have been generated every years. Site NT2-11, to be drilled into 1,600 m bsf, is located above the up-dip limit of the rupture area of the 1944 Mw 8.1 Tonankai megathrust earthquake. The spatial extension of the rupture area is considered by delimited by change in frictional property along the plate boundary which arrested dynamic propagation of the fault rupture. It is expected that spatial variation of seismic structure around the site reflects the change of the frictional behavior and need to be clarified as detailed as possible. Although P-wave velocity distribution and geometry of major reflectors are already shown by previous seismic survey using surface or ocean bottom recordings, seismic experiment using downhole seismic sensor should improve our understanding of the structure around the mega-splay fault and the mega-thrust fault such as: 1) spatial variation of S wave velocity 2) attenuation of seismic P and S waves 3) contrast of physical properties across the faults Better coupling against formation of the downhole seismic tool will improve the quality of S-wave data help to estimate S wave velocity with high reliability. Direct comparison of seismic data obtained by ocean bottom and downhole environment is invaluable for estimation of attenuation parameters, little of which has been obtained to date. Reflection coefficients not only for PP reflection previously observed but for SS, PS and SP reflections will provide us contrast in elastic moduli, density, etc. across the reflectors.

7 Fig. 1-1 Schematic image of walkaway VSP. Fig. 1-2 Index map showing the dive locations (808I and 1173B) during the K09-08 cruise.

8 July 22, 2009 during the dummy-run for VSP shooting.

9 Date Time (JST) Table 1. KR09-08 Cruise Log Event Comment 09/07/19 10:00 Depart JAMSTEC Pier at Yokosuka Head for BBOBS sites Acoustic communication to 3 BBOBS to extend the 09/07/20 06:00 recording time to October BBOBS#13 was not 09:15 Release BBOBS#13 and recover recording data Successful up to 50 km 18:30-21:00 Sync test using VHS-band radio distance 09/07/21 08:00 Test shooting of air-gun #3 09/07/22 Dummy run along the N-S VSP line, approaching Chikyu at ~14h Passing ~350m east of Chikyu 09/07/23 07:15 Obtain temperature profile using XBT 07:57-11:17 Launch 8 OBSs All successful 13:44-16:38 Deploy air-gun system 16:42-16:57 Test shooting for tuning 17:30-20:30 Acquire air-gun source signal waveform ~25 km south of Chikyu Move to VSP starting point along NS line 09/7/24 06:00 Get info from Chikyu, VSP start time=11:00 Starting air-gun shooting from ~14.5 nm south along 09:01 NS line 10:40 Problem in VSI shuttle, stop shooting Keep Kairei position at 13.3 nm south of Chikyu along 10:53 NS line 20:18 First shot, successfully acquired on Chikyu VSP along the southern part of NS line 60 m interval

10 09/7/25 02:00 Passing Chikyu Circle shooting Equal time shooting 07:00 Resume to NS line, continue walkaway 60 m interval 11:00 End of shooting at 30 km north of Chikyu 16:00 Disembark Shingu

Table 2-1, CHIKYU s principal specifications Length 210 m Beam 38.0 m Depth 16.2 m Draft 9.2 m Gross tonnage 57,087 tons Cruising speed Approx.

11 2. Explanatory Notes 2-1. Vessels CHIKYU and KAIREI (Fig. 2-1) are used for receiver and shooting vessel, respectively. CHIKYU and KAIREI s principal specifications are shown in Table 2-1 and 2-2, respectively. Fig Left: CHIKYU, right: KAIREI. Table 2-1, CHIKYU s principal specifications Length 210 m Beam 38.0 m Depth 16.2 m Draft 9.2 m Gross tonnage 57,087 tons Cruising speed Approx. 12 knots Range 14,800 nautical miles Accommodation 150 Main propulsion system Diesel electric propulsion Table 2-2, KAIREI s principal specifications Length 104 m Beam 16 m Depth 7.3 m Draft 4.5 m Gross tonnage 4,628 tons Cruising speed Approx. 16 knots Range Approx. 9,600 nautical miles Accommodation 60 (29 crew, 11 KAIKO 7000II support personnel, 20 research personnel)

Main propulsion system Diesel engines: 2,206kW 2 Main propulsion method Controllable pitch propeller 2 2-2. Air-gun and control unit Air-gun (Fig.

Table 2-3, KAIREI s air-gun and gun controller specifications. Navigation System SPECTRA (Concept Inc.) Gun Controller Digishot Ver3.1 (ION Inc.) Gun Configuration 1950cu.

12 Main propulsion system Diesel engines: 2,206kW 2 Main propulsion method Controllable pitch propeller Air-gun and control unit Air-gun (Fig. 2-2) and gun controller equipped in KAIREI are used. The air-gun and gun controller specifications are shown in Table 2-3. Fig. 2-2 Air-gun equipped with KAIREI. Table 2-3, KAIREI s air-gun and gun controller specifications. Navigation System SPECTRA (Concept Inc.) Gun Controller Digishot Ver3.1 (ION Inc.) Gun Configuration 1950cu.in 4 strings Total Volume 7800cu.in 2-3. Receivers in borehole 20 shuttles of Schlumberger s VSI (Versatile Seismic Imager tool) (Fig.2-3) receive various seismic waves. One shuttle of VSI has three component geophone-e accelerometers and one shaker. Table 2-4 shows main specifications of VSI sensor.

13 Fig. 2-3, VSI sketch after Schlumberger brochure. Table 2-4, VSI main sensor specifications. Sensor Geophone accelerometer (GAC-D) Sensitivity 0.5V/g +- 5% Sensor natural frequency 25Hz Flat bandwidth in acceleration: 2 to 200Hz Dynamic range >105 db at 36 db gain Distortion < 90 db Digitization 24-bit analog-to-digital converter Detail information of tool specifications is available from OBS Table 2-5, OBS sensor specifications. Sensor Velocity sensitive geophone (L-28LB) Sensitivity 29.53V/m/s Sensor natural frequency 4.5 Hz Sensor specificatioin including response curve can be found in ftp://ftp.sercel.com/pdf/brochures/geophoneshydrophones.pdf

14 Fig OBSs Time synchronization system A VHS radio wave system was used. During the cruise we checked whether the signal can be detected at far-offset, and found it worked fine to the 50 km distance. Fig. 2-5 VHS radio time synchronization system.

15 3. Broadband seismic observation at the seafloor Several lower-frequency seismic events including the tremors were detected by the Hi-net stations on land. In order to observe such events at the place much closer to the hypocenters, we deployed 4 broadband ocean bottom seismometers (BBOBS) by R/V Kaiyo (KY08-07) and have been recording since last July (Table 3-1). We also deployed 36 short-period ocean bottom seismometers at that time by R/V Kaiyo and recovered them after three months by R/V Kairei (KR09-11). In this cruise we tried to communicate to the recorder of BBOBS by acoustics to extend the recording period for three sites of them (Sites of 5B, 8B and 16B) for two months. The stopping date of the record was changed from Aug. 1 to Oct. 10 (see the logging listed below). We have a plan to recover them in early October. And we recovered one BBOBS (Site of 13B; Fig. 3-1) because the recorder has a trouble before starting to record. The electric current was 1.6 A for releasing from the anchor for about 6 minutes. Table 3-1. Location of BBOBSs Station Lat (N) Lon (E) Depth(m) Operatin 5B(D) Change setting 8B(A) Change setting 13B(B) Recover 16B(C) Change setting Example for the logging data for acoustic communication(site 5B; Code: SI2-811) c811 CALL,0811,03868, ,N, ,E,0,R00V0.0A e811, TFE,0811,03868, ,N, ,E,0, f811,gs TFF,0811, ,N, ,E,0,[ ] RUN 1U e811,ct TFE,0811,03866, ,N, ,E,0,< Timer Mode > e811,et 09 TFE,0811,03865, ,N, ,E,0, e811,10 10 TFE,0811,03864, ,N, ,E,0,

f811,vt TFF,0811,0000.0000,N,00000.0000,E,0,??:2008/07/26-00:00:00 ET:2009/10/10-00:00:00 e811,q TFE,0811,03862,0000.0000,N,00000.0000,E,0,< Top > f811,gs TFF,0811,0000.

16 f811,vt TFF,0811, ,N, ,E,0,??:2008/07/26-00:00:00 ET:2009/10/10-00:00:00 e811,q TFE,0811,03862, ,N, ,E,0,< Top > f811,gs TFF,0811, ,N, ,E,0,[ ] RUN 1U Fig. 3-1 Recovered BBOBS deployed at the site of 13B because of troublesome of the recorder.

4. Deployment of ocean-bottom seismometers It is important to know both spatial variation of S wave velocity and attenuation of seismic P and S waves in order to understand the frictional nature of

We have developed eight ocean-bottom seismometers (OBS) (Fig. 4-1; Table 4-1) on July 23rd. It is possible to throw the OBSs down from a vessel by free fall.

17 4. Deployment of ocean-bottom seismometers It is important to know both spatial variation of S wave velocity and attenuation of seismic P and S waves in order to understand the frictional nature of the maga-splay fault detached from the plate boundary. In order to calculate these underground structures, it is necessary to deploy seismic sensors on the sea bottom as well as down-hole sensors. We have developed eight ocean-bottom seismometers (OBS) (Fig. 4-1; Table 4-1) on July 23rd. It is possible to throw the OBSs down from a vessel by free fall. A short-period seismometer with an eigen-frequency of 4.5 Hz is used to measure signals from air guns. The sensor, data logger, and batteries are packed into a glass sphere. It is possible to record continuous data related to the vertical and two horizontal components from 09:00 on July 23rd to 00:00 on August 1st with a sampling rate of 400 Hz. The OBSs will be recovered by a pop-up system at the beginning of next August. The locations of the eight OBSs are listed in Table 1 and are shown in Fig The locations are shown as the point where the OBSs were dropped on from the vessel. Fig 4-1. Ocean bottom seismometers on board ship

18 Fig. 4-2 Map showing the location of the ocean bottom seismometers

19 Table 4-1. Location of ocean bottom seismometers Station Latitude Longitude Depth Time (UTC) OBS1 33º N 136º E 2064 m 2009/07/23 02:17:33 OBS2 33º N 136º E 2062 m 2009/07/23 01:50:20 OBS3 33º N 136º E 2046 m 2009/07/22 22:57:00 OBS4 33º N 136º E 2059 m 2009/07/22 23:24:23 OBS5 33º N 136º E 2062 m 2009/07/22 23:56:55 OBS6 33º N 136º E 2061 m 2009/07/23 08:32:00 OBS7 33º N 136º E 2060 m 2009/07/23 01:14:59 OBS8 33º N 136º E 2059 m 2009/07/23 01:43:10 The OBSs were dropped on from the vessel at the times.

Despite bad visibility, Kairei was able to approach Chikyu to 350m from her center (not from her edge!). It was such a close distance (Figs. 5-1 and 5-2). Fig.

20 5. Walkaway VSP Experiment 5-1. Dummy run result Test run was carried out along the N-S VSP line, approaching Chikyu at ~14h of July 22. No air-gun shooting was conducted, but just steamed simulating the ship track during the walkaway VSP operation. Despite bad visibility, Kairei was able to approach Chikyu to 350m from her center (not from her edge!). It was such a close distance (Figs. 5-1 and 5-2). Fig. 5-1 Ship track during the dummy run test Source signal acquisition by Kairei hydrophone On July 23, the air-gun system was successsfully deployed, followed by a test shooting and acquisition of source signal waveforms. Fig. 5-2 Example of source waveform.

21 5-3. Walkaway VSP (Fig. 5-3) The walkaway VSP operation was carried out on July 24 to July 25, At 08:35 am of July 24, test shoot was conducted to 08:40, then at 09:01 we started shooting along the NS line, from ~25 km south of Site C0009 (Chikyu location). Position was 33_14.64 N, 136_40.83 E, and Kuroshio current was 3.9 knot toward 107deg. Steaming spped ( ground speed) was only 0.9 knot toward 330deg. At 10:40 A trouble of VSI shuttles was found. At 10:53 we terminated the shooting, and waited for Chikyu SLB engineers to retrieve shuttles and check & repair, estimated to take ~4 hours. Shoot was terminated After fixing the problem of VSI shuttle, at 20:18:04 JST, we finally obtained our first shot data on Chikyu, at ~25 km south of chikyu. This caused us ~10 hours delay. Since then, we basically did not have any problem so far. Some clear waveforms were recorded. We started data acquisition at ~25 km south of chikyu along the NS line (actually heading 330deg, almost parallel to 3D inline direction) at every 60 m. After passing by Chikyu at ~2am today (July 25), we conducted one circle shooting with 3.5 km radius around Chikyu. It was completed this morning, then we resumed to the NS line to continue the rest of the line. CUrrently we are ~10 km north along the NS line, and plan to keep shooting until 11:00am today. A quick-look achievement of the W-VSP is as follows: *NS line walkaway VSP, 25km south to ~30 km north with 60 m interval *Circle shooting VSP, 3.5 km radius And suprisingly they were acheved in less than 15 hours.

22 Fig. 5-3 Air-gun array during their shooting.

R/V Kairei Cruise Report KR Seismic study in the northwestern Pacific region. Jan. 4, 2011 Jan. 20, 2011

R/V Kairei Cruise Report KR Seismic study in the northwestern Pacific region. Jan. 4, 2011 Jan. 20, 2011 R/V Kairei Cruise Report KR11-01 Seismic study in the northwestern Pacific region Jan. 4, 2011 Jan. 20, 2011 Japan Agency for Marine-Earth Science and Technology (JAMSTEC) Contents: 1.Cruise Information: