Keck Expedition 2004
August 10, 2004 Day 12
Update for Tuesday, August 10 - Debra Stakes
Today we have a bonus dive to do a little more exploration for the other Keck investigators before we pack up and head for Newport. It’s a bonus dive because our extremely ambitious schedule was accomplished in less time than expected. We have abundant praise for the energy and skill of both the ROV pilots and the Western Flyer crew for making everything work with such apparent ease.
Our dive target today again arrived as a satellite fax and telephone call. Canadian seismologist George Spence on the John P. Tully found an interesting mound just in front on the accretionary slices of ocean crust that I described yesterday. On the seismic sections this mound appears to be related to a vertical movement of fluids or fluidized rocks through the ocean crust. Such phenomenon have been related to mud volcanoes or other methane degassing structures. We were given the task of searching for evidence of the origin of this conical structure and determining whether there was any sign of active venting.
Our dive track was planned to begin at the southwest corner of the mound and drive up the steepest sections (based on our high resolution bathymetry). Past ROV fieldwork has shown us that in sediment-covered terrains such as this one, the most likely rock outcrops are to be found on the steepest slopes or the eroded gullies. The flatter base of the structure is all very normal looking lumpy sediment. Even the steepest walls are over 50% sediment-covered. The outcrops that are visible are also heavily populated by all of the normal benthic fauna that prefer to attach to hard bottom. Both sides of the mound had such steeply dipping beds exposed. It was frustrating for me (as a geologist/geochemist) to not be able to take the time to grab a sample to examine on deck. It all looked like terrigenous sediments, but every once in awhile you could peek under a slab and see some provocative broken material of different origin. We patiently looked everywhere for evidence of active fluid flow, but none could be found. A null result may not be the most exciting but it is still important information for the overall program. So I got to call the end of the dive before the very last minute and we cheered, recovered the vehicle, and headed for port.
The ROV Tiburon completed operations on the Nootka Transform today at 2 pm and the Western Flyer is steaming for Newport, Oregon. We completed our instrumentation program, which included the recovery and redeployment of eight seismometers, all of which returned beautiful data sets, and the deployment of five new systems. All of this was accomplished in less time than planned. This was due to a variety of factors including accommodating seas, a talented and hard-working Operations Group, a cooperative ROV, and dependable instrumentation. The seismologists onboard are marveling at the overall quality of the data. The data back-up is ongoing and the small inconsistencies are being logged and analyzed. This information will be used to improve the software and methodology for next year.From a broader perspective, we are part of a collaborative group working on a common data set that ultimately will be available on a public database. There will be new insights about the distribution of earthquakes in the Endeavour and Nootka regions from these data and their relationship to the subsurface movement of the fluids necessary to support microbial life. The data will also become a permanent treasure trove of potential new insights awaiting work by future scientists. This is the nature of the observatory science--collaborative, multidisciplinary and waiting to be discovered.
For now, however, the shipboard science party provides an example of the data obtained from the Guralp CMG1T at KEBB. This is the broadband station on the southwest flank of the Endeavour Segment. The event in this figure occurred on September 2003. It is a magnitude 8.5 earthquake in Japan (41.81 degrees N; 143.91 degrees E), about 6900 km from our site. The data provided are unfiltered, and include (from top to bottom) E-W axis, N-S axis, and vertical axis. Note the high quality signal-to-noise ratio on the vertical (z) axis is before the earthquake, which helps seismologists in picking the arrival time of the first seismic waves. This compares favorably with land-based stations.
From the sea.
Will Wilcock, Paul McGill, Debra Stakes, Taimi Mulder, Doug Toomey, Andrew Barclay