Integrating science and technology
at the Nankai Trough subduction zone

Cruise reports!

From co-chief scientist, Nathan Bangs.

- Report 5 (Final Report, Monday August 16, 1999)
- Report 4 (Tuesday, August 3, 1999)
- Report 3 (Tuesday, Jul 20, 1999)
- Report 2 (Tuesday, July 10, 1999)
- Report 1 (Wednesday, June 23, 1999)

Report 4 (Tuesday, August 3, 1999)
From Nathan:
In the past 12 days since leaving Kochi we have made reasonable, although interrupted, progress infilling in the remainder of the 3-D survey area. We have acquired 21 lines in last 12 days. Unfortunately, we are beginning to get into the midst of typhoon season. Tropical depressions and typhoons seem to be generating regularly to our southeast, and building and migrating toward our survey area. Tropical depression Neal passed to the south of us July 26 th and 27th and dealt us a glancing blow. Seas kicked up with a large swell and very choppy. We encountered 45 kt. winds and 25 ft. seas that tossed books, furniture, computer monitors and scientists all over the ship. The weather required that we retrieve the guns and streamer and bounce around for nearly two full days before resuming data acquisition. During the week after Neal we re-deployed the gear, seas were calm and data were very quiet, but tropical depression Olga was building to the south. Currently Olga has built into a moderate typhoon, but it has passed 500 miles to our southwest. Fortunately we have missed a severe blow from this storm, but we are close enough to it that it has had us on edge about retrieving the gear and it has heightened the sea and cause noisy records. It looks like Olga will pass us by with minimal impact. Who knows what is brewing in the tropics for us next.

Currently we have 5 lines remaining to finish filling in an 80 x 7.5 km survey area. Following the completion of those five lines, we will begin re-shooting problem lines and filling data gaps. Re-shooting will probably take one of the two remaining weeks we have out here. Following the re-shoots we will have some time left to add a few more lines and increase the width of the survey. This all assumes that our weather holds, and we can solve some of our current gun problems. One of the gun chambers is wearing out and is not holding a seal. We are currently trying to modify a larger chamber for a suitable replacement, but it is not clear yet if this will work.

The on board processing and quality control is going well. We have been able to keep up with noisy trace editing until our most recent encounter with bad weather. We should be able to get back up to date as soon as the weather calms down. We have also been able to keep up with the initial stacking and migration. Data have been loaded into Geoquest for initial examination and to look for problem lines. So far we have found few data acquisition problems with the lines examined so far.

Report 3 (Tuesday, July 20, 1999)
From Nathan:
We are now finished with the data acquisition for the first half of the experiment, and are preparing to head into Kochi for a two-day port stop. Recent calm weather and minimal equipment problems have enabled us to fill in a substantial portion of the survey area, and finish the first leg in good shape for the second half of the experiment. In the past ten days we have acquired 21 of the 81 planned lines. Most of that data has minimal noise because of the good weather and calm seas. Our only significant problem has been ship traffic, which has required us to dive the streamer to 25 m numerous times to avoid further damage.

At the midpoint of our experiment, we are doing reasonably well. We have now shot 49 of the 81 planned lines in the 3-D grid. Most of these data have been acquired in good weather with minimal equipment problems, such as bad channels and inoperative guns. However, there are sections of lines that will require re-shooting on the second leg. Most of these areas are due to noisy data from bad weather, tape drive failures, and other ships interfering. Currently we have about 2 -3 days of reshooting required and we will begin reshooting once we have about 65 of the 81 planned lines.

The QC and preliminary processing has been underway during the first leg and most of the data have been examined. All field tapes have been re-sampled and copied to DLTs. Shot gathers have been edited using statistical analysis and by individual trace examination. About 65 % of the data have been edited. Preliminary processing has included some velocity analysis, nmo, stack and migration. Currently about 35 % of the data have been processed and we have begun loading lines into Geoquest for initial examination. The navigation of the streamer from the compass data has been successful. We are able to reconstruct streamer positions that lie, on average, within 20-30 m of the tailbuoy positions where we have tailbuoy data. The reconstructed streamer positions are used in generating UKOOA files that have successfully been loaded into Focus and Promax and used for 3-D binning and generating bin fold maps. Preliminary shot kill files have been generated for about half of the lines based on examination of the compass, and gun characteristics. These files will eventually be used to eliminate shots that are outside specifications, or to determine where additional reshooting will be needed.

From the initial 2-D migrated stacks, the data are impressive. There are numerous reflections from stratigraphic horizons and fault planes. A striking, well-imaged sequence of folds and thrusts begins at the deformation front and extends approximately 60 km. Beneath this sequence the basement can be traced along nearly the entire 80 km of our profiles. We expect these data will be even more impressive with the additional data from the next leg and full 3-D processing.

Report 2 (Tuesday, July 10, 1999)
From Nathan:
We have now been underway for 23 days. After problems the first week we have now been making better progress with the data acquisition. Currently we have collected 30 of the 81 lines in our 8 x 80 km 3-D grid. Most of the data look good with the exception of a few lines that were acquired during rough weather and were apparently noisy from the high sea state. Generally winds have been less than about 20 kts. except on two occasions. Weather has been one of the main reasons slowing our progress, as two storms so far have cost us about two days of acquisition.

Our other main problem so far has been ship traffic. In one instance, we had to deviate from our line to avoid collision with at tanker that was adrift without power. We have had 5-10 ships a day that need to change course to avoid our streamer. We have been very successful in contacting ships and diverting them, but we have still had 5 ships pass over the streamer. In one instance, a ship was successfully contacted and instructed to pass behind us, but after altering course to avoid the streamer, it altered course again and cut across it. After the ship crossed, we lost contact with the tail 1/4 of the streamer and suspected that we had lost it. After pulling in all of the guns and streamer, we discovered the streamer was indeed hit by the ship and all but the two strength members of the cable were severed. Luckily we were able to retrieve the entire streamer with minimal loss. With the damaged section replaced, and a large amout of fishing tackle removed, we redeployed the streamer and a repaired tailbuoy.

In the past two days since the redeployment, both the streamer and the tailbuoy gps positioning have been working well. Navigation processing and quality control are well underway with the first large UKOOA files generated today. We are using Sioseis, Promax, Focus and Geoquest software for tape transcription, quality control, trace editing, and processing of selected lines. Even with the 8 computers brought along by the science party empty seats are rare.

We are hoping that we can keep up our current rate of acquisition and on board processing until we head for Kochi on the 19th for a two day break prior to the second leg.

Report 1 (Wednesday, June 23, 1999)
From Nathan Bangs:
We are now well underway on EW9907 3-D survey of the Nankai Trough. We left port on Friday June 18th at 10:00 AM with 23 scientists and 20 crew and headed for the survey area. After an initial battle with rough weather and some seasickness, we arrived at the site with about 1.5 days of transit. Strong four knot currents slowed our progress during the transit. We made contact with our chase boat at the southern end of the survey area and began deploying the equipment on the 19th. The initial streamer deployment required work to attach lead weights to adjust the streamer buoyancy for the water temperature and salinity. Following about 12 hours of streamer work we discovered that the tail buoy differential gps receiver stopped working when the streamer was nearly completely deployed. This required recovering the streamer and changing the radio antennae.

After re-deploying the streamer we began shooting our first line. Our first line was a regional 2-D line through the center of the 3-D grid and extending 40 km to the north and south. On the northern extension of the line, just south of the Muroto Peninsula, we encountered both heavy ship traffic and strong currents. Currents had us heading 270 degrees to make good on a 314 degree course. The tail of the streamer was 3 km offline. Because of these problems we terminated this 2-D line prematurely, 20 km northwest of the 3-D grid, to begin shooting the 3-D grid. At the start of shooting the 3-D grid, the seas picked up and after about 5 km on the line the tail-buoy flipped over and we lost our tailbuoy positions. Fixing the tail-buoy required recovering the streamer once again. Following the third deployment of streamer and guns, we lined up to begin shooting grid lines and once again we lost our transmissions from the tail-buoy. Currently we are nearing the end of our first 3-D grid line and have temporarily given up on the tail-buoy positioning. We expect to continue shooting for a while until we can devise an adequate solution for the tail-buoy.

Overall, the data that we have acquired look very good. The source pulse is clean with a very small bubble. The new streamer is very quiet in calm weather but is noticeably noisier when the seas pick up. Everyone seems to be adjusting to life at sea. We expect to be making up for lost time with continuous acquisition for the next few weeks.

From Amanda McCutcheon - A student's perspective.

- Report 3 (Wednesday, July 14, 1999)
- Report 2 (Tuesday, June 29, 1999)
- Report 1 (Thursday, June 24, 1999)

Report 3 (Wednesday, July 14, 1999)
With mid-July approaching, we are nearing the end of our first leg of the cruise. I think that everyone is looking forward to the short port in Kochi. For the past few days, the weather has been sunny and the seas have been calm. Our data has little noise, and aside from losing our tail buoy GPS, data aquistion has been going smoothly. However, there is now a tropical depression to the southeast of us. A few of us had the opportunity to tour the engine room. The chief explained some of the mechanics of the ship, and we were able to ask questions about the engine processes. All of the mechanisms and pipes are color-coded according to their task. For instance, all of the fresh water apparatus are painted blue. The engine room is very organized and very hot. With all of the noise down there, most of the tour consisted of reading and pointing to the labels. I am amazed at the self-efficiency of the ship. We make our own water, and the crew has the abilities to build many of the equipment should it malfunction. I also went out on the boom a couple of days ago. That is the farthest I have ventured from the ship in three weeks. It was a very calm day, and I was able to see the large bubble produced by the airguns. Now I can appreciate the risk that the gunners take to operate the airguns. With the nice weather, we were able to have Sunday Bar-B-Q out on the deck. That is only the second time we have been able to do so because of rainy weather. The change of pace was welcomed. With the help of various scientists, our streamer has avoided any recent collisions. Yesterday, one of the Japanese scientists was called to the bridge in order to communicate with an oncoming vessel. However, Yasu soon discovered that the crew of the other boat was not speaking Japanese. Instead, he was speaking Chinese. So Zhao came to the rescue and they changed coarse just in time. If we have any German, Spanish, or Russian encounters, we should also be okay. There is definently a plethra of culture and background on this boat...all with a common goal. I will keep you updated with any turn of events.

Report 2 (Tuesday, June 29, 1999)
Life onboard the ship is becoming routine, although a bit mundane. However, I do look forward to being on "watch." During this time, the watchstanders are required to record location, cmg, speed, and log every half hour along with changing the tapes when they are full. Watchstanders also make a near trace plot of the first shot of every tape/file in order to identify any problems with the data or tape. This plot is made by a simple program that I wrote on SIOSEIS. We also keep an hourly record of the current. Carmen, a grad student from UC Santa Cruz, wrote a program using PERL that automatically calculates the current with just a few values. In general, we have had a slow start.

The Americans and the Japanese are learning alot from one another. I am on shift with a Japanes student named Sumito. I have helped him with some of his English pronunciations, and he has helped me with Japanese pronunciations. The Japanese are very eager to add to their vocabulary and understanding of english colloquialism. I have been very interested in the Japanese way of life. The Japanese scientists are very approachable and open about their personal lives. Overall, it seems that we are not that different.

Report 1 (Thursday, June 24, 1999)
We left the port in Yokohama on Friday, and we are now on our 5th day of research. Unfortunately, there have been some GPS problems with the tail buoy, but hopefully these problems have been reconciled for the time being. We are shooting data again.

While in Yokohama, some of the science staff, including myself, had time to explore the city. Yokohama seems to be a very international city, however, we had to learn a few Japanese phrases in order to use the subway system. The Japanese people are very friendly and willing to help foreigners in any way possible. We navigated our way through the city and shopped, ate, and visited tourist sites such as a 14th century temple and the 69th floor lookout point in a tower.

With our trip underway, we are slowly becoming accustomed to life on the boat. There is a 6-hour shift for watch standers along with some individual assignments. While on duty, the watchstanders keep a record of location, speed, and depth in half-hour increments. Also, the tapes must be rotated, and plots are made of the first shot of each tape to make sure there are no problems. Also, the current is calculated regularly. There has been some processing work done by the P.I.'s, while the technical staff is helping to make sure all of the programs are running smoothly. Once more data is collected, we will have "homework assignments" to complete in our spare time. Although the seas have been rough for the past two days, everyone seems to be settled and ready to work!