NT10-18 NATSUSHIMA / HYPER-DOLPHIN

Transcription

1 NT10-18 NATSUSHIMA / HYPER-DOLPHIN Kumano-Nada October 2010 Earthquake and Tsunami Research Project for Disaster Prevention JAMSTEC

2 TABLE OF CONTENTS 1. INTRODUCTION 2. SCHEDULE 3. DIVE RESULTS 4. CONCLUSIONS Appendix (in Japanese)

3 1. INTRODUCTION Japan has started installing the offshore cabled observatories for disaster mitigation purposes since late 1970s. We have already developed seven cabled observatories around Japan, in particular along the Pacific Rim, and brought us invaluable information. For example, the 2003 Tokachi-oki earthquake of M8.0, seafloor phenomena such as a generation process of tsunami, seafloor uplifts, etc., were observed (Mikada et al, 2006). At the 2004 off Kii peninsula earthquake of 7.4, the offshore observatory could detect tsunami 20 min before its arrival at the nearest coast (Matsumoto and Mikada, 2005). Since 2006, Japan Agency for Marine-Earth Science and Technology (JAMSTEC) has started to develop a new dense network system by using sub-marine cable off Kii-peninsula, where the last mega-thrust earthquake named Tonankai earthquake was took place in The Headquarters for Earthquake Research Promotion in the Ministry of Education, Culture, Sports, Science and Technology (MEXT) has estimated that the probability of the next Tonankai earthquake is 60 to 70 % in the next 30 years, because the recurrent interval of the plate boundary earthquake is approximately 100 to 150 years there. Thus, the offshore seismic monitoring system for the forthcoming Tonankai earthquake is urgently needed to mitigate future disasters form the earthquake and resulting tsunami. The system to be developed contains twenty seismometers, twenty tsunami meters, and other geophysical sensors covering the expected Tonankai earthquake source region in order to monitor both long-term seismic activities and mega-thrust earthquake and tsunami. Our goals are postulated to accomplish high precision earthquake prediction modeling, to detect precursory prior to the mega-thrust earthquake, and to contribute to mitigate disaster caused by the earthquake and the tsunami by providing the information, in addition to developing the network system itself. First DONET science node and observatory was established at A-3 location by using ROV Hyper-Dolphin during NT10-04 cruise on March The following survey was done on May 2010, which installed three science nodes and three observation instruments on the seafloor. The present NT10-18 cruise is scheduled to increase observatories to connect science node and observatories by extension cable, and to deploy more observatories to round out the original observatory network layout as shown in Fig. 1.

4 Figure 1 Map showing the deep-sea network observatory to be deployed off Kii-Peninsula. Circles and dots represent the observatories and the science nodes, respectively

5 2. SCHEDULE The present NT10-18 cruise consists of the following four main missions to establish DONET network observatory by ROV Hyper-Dolphin. (1) Sensor installation (2) Extension cable laying operation between node and observatory (3) Burial hole conditioning (4) Backfilling burial hole operation In NT10-18 cruise, we could carry out twelve dives covering the above operations. The time window of the present cruise was 04 October to 17 October. The summary of Hyper-Dolphin operation is listed in the below table. Table 1 Summary of NT10-18 cruise Date Location Operation 04 October JAMSTEC Departure at JAMSTEC to Kumano-Nada 05 October Kumano-Nada Dive #1194 and #1195: Minor adjustment needed on ROV and the extension system 06 October Kumano-Nada Dive #1196: Extension cable laying of A-2 observatory 07 October Kumano-Nada Dive #1197: Minor adjustment needed on extension cable, but fixed 08 October Owase-Bay Evading Navigation 09 October Owase-Bay Evading Navigation 10 October Kumano-Nada Dive #1198: Backfilling burial hole by Sand Feeder 11 October Kumano-Nada Dive #1199: Extension cable laying of A-4 observatory 12 October Kumano-Nada Dive #1200: Extension cable laying of E-17 observatory 13 October Kumano-Nada Dive #1201: Burial hole conditioning of D October Kumano-Nada Dive #1202: Sensor installation of D October Kumano-Nada Dive #1203 and E1204: Burial hole conditioning of E19 and E October Kumano-Nada Dive #1205: Burial hole conditioning of B-6 17 October JAMSTEC Return to JAMSTEC

6 3. DIVE RESULTS We carried out twelve dives (Dive #1194 through Dive #1204) in total with ROV Hyper-Dolphin during our present NT10-18 cruise. Summary of each dive are summarized as follows, (1) Dive #1194 on 05 October We planned to do cable lay between the node A and the observatory A-2, but ROV had a minor problem right after the dive. Therefore this dive was cancelled on the way of the dive. Photo 1. ROV with extension cable laying system

7 (2) Dive #1195 on 05 October After fix the ROV minor problems occurred on the #1194 dive, we tried to do extension cable laying operation again. But we found that the cable drum attached with ROV had a bit problem. The problems is what is cable drum keeps free wheel condition and unexpected cable payout causing twining around the drum shaft during the dive due to the water current. This dive was also cancelled and we made an attachment to fix the cable drum rotation during diving down till the ocean bottom. Photo 2. Unexpected cable drum rotation during Dive #1195 Photo 3. An attachment for cable drum stopper

8 (3) Dive #1196 on 06 October We could prevent unexpected rotation of the cable drum during the diving down in terms of the stopper. We successfully carried out extension cable laying operation with no trouble between Node A and the observatory A km extension cable laying operation was done during the current dive with 11 hours dive. After connecting to sensor package, cable communication regarding the observatory A-2 is confirmed to be good from Furue landing station. The node connector is used at No.1 port of Node A, and the extension cable is used with No.9 cable colored by black. The location and sensor IDs of observatory A-2 are as follows, N, E, 2011m, Sensor ID: SPKG A040 Photo 4. Cable connection to the node A Photo 5. Cable drum near the observatory A-2

9 Photo 6 Cable connection to the sensor package Photo 7 Sensor layout at observatory A-2

10 (4) Dive #1197 on 07 October We planned to carry out extension cable laying operation between Node A and observatory A-4. We connected interface of the extension cable to No.8 port at Node A, then right after laying extension cable, we had an accident to take place a kink, i.e., an abnormal loop on the extension cable. Our operation had to suspend and we decided to go back. This is because we could not check the status at that time, so we decided to recover the extension cable. After recovering the extension cable, we checked the cable had not been damaged physically at all. Both the optical fiber liens and power feeding copper lines are well worked on the board. We judged that this extension cable was reusable in the next operation. We changed the procedure to lay extension cable near at the beginning of operation. Photo 8 Kink occurred in the extension cable Photo 9 Extension cable laying at the beginning (left: until Dive #1197, right: now)

11 (5) Dive #1198 on 10 October Hyper-Dolphin Dives on 08 and 09 October were cancelled due to the bad weather. On 10 October, we carried out backfilling operation at observatory A-2 by using Sand Feeder newly designed by Dr. Yokobiki. It took a few minutes to complete the seismic sensor package filled by sand. It made us possible to short operation time to complete backfilling. Photo 10 Sand Feeder equipped with Hyper-Dolphin Photo 11 Seismic sensor package in the burial hole (left: before backfilling operation, right: after operation)

12 (6) Dive #1199 on 11 October We carried out extension cable laying operation between Node A and observatory A-4, which was approximately 9.5 km length. The observatory has been booted up after connecting the science cable to the sensor package. We checked the communication status well. The node connector is used at No.8 port of Node A, and the extension cable is used with No.8 cable colored by white. The location and sensor IDs of observatory A-4 are as follows, N, E, 2054m, Sensor ID: SPKG A080 Photo 12 Extension cable interface connecting to No.8 port of Node A Photo 13 Extension cable laying operation by Hyper-Dolphin

13 Photo 14 Other side interface connecting to the sensor package Photo 15 Sensor layout of observatory A-4

14 (7) Dive #1200 on 12 October Extension cable laying operation between Node E and observatory E-17 was completed, and booting up of the observatory was performed in this commemorative dive. After connecting science cable, both the node E and the observatory E-17 have been booted, and we made sure the communication is well. We have laid the science cable in approximately 9.0 km long. The node connector is used at No.7 port of Node E, and the extension cable is used with No.11 cable colored by blue. The location and sensor IDs of observatory E-17 are as follows, N, E, 2054m, Sensor ID: SPKG A060 Photo 16 Extension cable interface connecting to No. 7 port of Node E

15 Photo 17 Other side interface connecting to the sensor package Photo 18 Sensor layout of observatory E-17

16 (8) Dive #1201 on 13 October We carried out burial hole conditioning by using the suction system named DROTHY and tried to install the seismic sensor package into the burial hole at observatory D-16. After conditioning the burial hole, we realized that the seismic sensor package could not be deployed into the hole smoothly. Therefore, we left the seismic sensor package at the bottom, and we would recover another day. We discussed this phenomenon on board, and we considered two reasons; one is sediment is still left inside the hole, and the other is two different diameters holes does not coincident with each other. At last, we would try to do hole conditioning and watch the status inside the hole carefully. Photo 19 Burial hole conditioning using by DROTHY Photo 20 Sensor installation into the burial hole

17 Photo 21 Sensor package installation not perfectly

18 (9) Dive #1202 on 14 October We planned to recover seismic sensor package left in previous Dive #1201. We recovered the seismic sensor package from the burial hole at first. And we checked the condition inside the hole, and we did make the hole adjustment again. The hole condition became better than the originals after adjustment, we put the seismic sensor package into the hole again and put the pressure sensor package. As a result, we did not recover the sensor, and we successfully installed the sensor at observatory D-16. The location, ROV-Homer ID, and sensor IDs of observatory D-16 are as follows, N, E, 1970m, Homer-ID: 13, Sensor ID: SPKG A090 Photo 22 Seismic sensor package installation at D-16 Photo 23 Pressure sensor package (SPKG A090) installation near the burial hole

19 (10) Dive #1203 on 15 October We performed burial hole conditioning at the observatory E-19 by using DROTHY. Although burial length of the casing somewhat seems not to be enough for sensor installation, i.e., 50 cm rising up from the bottom, we carried out conditioning inside the casing. We need to discuss that we use this casing or we will install new one instead. The location measured by Dive #1203 and ROV-Homer ID of observatory E-19 are as follows, N, E, 1908m, Homer-ID:23 Photo 24 Burial hole conditioning at E-19 Photo 25 View of burial hole after conditioning by DROTHY

20 (11) Dive #1204 on 15 October After conditioning the burial hole at observatory E-19, we continue to do same operation at observatory E-18. The bottom casing at E-18a has been installed in a good condition, and we have put the cover designed by Mr. Kodera on it. The location measured by Dive #1204 and ROV-Homer ID of observatory E-18 are as follows, N, E, 2048m, Homer-ID:31 Photo 26 Burial hole conditioning at E-18 Photo 27 Cover put on the burial hole

21 (12) Dive 1205 on 16 October This was the last dive of the present NT10-18 cruise. We carried out the burial hole conditioning at observatory B-6 by using DROTHY. After adjustment, we put cover on the bottom casing as done at observatory E-18. The location measured by Dive #1205 and ROV-Homer ID of observatory B-6 are as follows, N, E, 2496m, Homer-ID:90 Photo 28 Burial hole conditioning at B-6 Photo 29 Cover put on the burial hole

22 4. CONCLUSIONS In the present NT10-18 cruise, three new observatories were able to be activated, one candidate observatory was installed and three candidate sites were conditioned. This is a very excellent result for DONET project. We can expect several more observatories activation in the forthcoming cruise scheduled Dec to Jan End of Report.