The western Nankai 3-D experiment was conducted in 1999 on the R/V Maurice Ewing Legs 7 (EW9907) and 8 (EW9908). This is a collaborative project between UTIG, University of Hawaii, University of California, Santa Cruz, University of Tokyo, Japanese Geological Survey and STA JAMSTEC. The project consists of 81 dip lines ( Line numbers 92 through 172) each 80 km long with a shot spacing of 50 m. The streamer was 240 channels, 6 km long. There are also a few lines outside of the region, lines Nan-1 (the first line shot and has no navigation), 19, 20, 40, 42, and 50. The goal of the study is to examine changes in physical properties along the thrust as it changes from aseismic to seismic expression. Understanding this transition from compaction and aseismic slip to brittle failure is a major unknown in understanding lithospheric consumption and earthquake dynamics.
Chief Scientists:
Nathan L. Bangs Shin'ichi Kuramoto
Principal Investigators:
Nathan L. Bangs (NSF 9730637) Thomas H. Shipley (NSF 9730637) J. Casey Moore (NSF 9802264) Greg F. Moore (NSF 9802295) Julia K. Morgan (NSF 9802295) Asahiko Taira Shin'ichi Kuramoto
Data Originating Institution:
Institute for Geophysics, University of Texas at Austin
Funding Agency:
National Science Foundation Ocean Research Institute, University of Tokyo Geological Survey of Japan
Scientific References Moore, G.F., Taira, A., Klaus, A., et al., 2001, Proceedings of the Ocean Drilling Program, initial reports, deformation and fluid flow processes in the Nankai Trough accretionary prism, covering Leg 190 of the cruises of the drilling vessel JOIDES Resolution, Sydney, Australia, to Yokoha, Proceedings of the Ocean Drilling Program, Part A: Initial Reports, edited by Cagle, L. J. and Sherar, K.R., published by Ocean Drilling Program (College Station, TX), vol. 190, DOI: 10.2973/odp.proc.ir.190.2001. URL: http://www-odp.tamu.edu/publications/190_IR/190TOC.HTM
Bangs, N., Shipley, T., Gulick, S., Moore, G., Kuromoto, S., and Nakamura, Y., 2004, Evolution of the Nankai trough decollement from the trench into the seismogenic zone: Inferences from 3D seismic reflection imaging, Geology, vol. 32, p. 273-276.
Gulick, S., Bangs, N., Shipley, T., Nakamura, Y., Moore, G., andKuramoto, S., 2004, Three-dimensional architecture of the Nankai accretionary prism's imbricate thrust zone off Cape Muroto, Japan: Prism reconstruction via en echelon thurst propagation, Journal of Geophysical Research, vol. 109, p. B02105, DOI: 10.1029/2003JB002654.
Bangs, N., Shipley, T., Moore, G., Moore, C., Gulick, S., Kuramoto, S., Nakamura, Y., and Park, J.-O., 2005, The 3-D Architecture of the Nankai Trough Accretionary Wedge and the Development of the Seismogenic Zone, MARGINS Newsletter, vol. 14 (Spring 2005), p. 1-5, 28.
Pisani, P. ., Reshef, M., and Moore, G., 2005, Targeted 3-D prestack depth imaging at Legs 190-196 ODP drill sites (Nankai Trough, Japan), Geophysical Research Letters, vol. 32(20), p. L20309, DOI: 10.1029/2005GL024191. URL: http://www.agu.org/journals/gl/gl0520/2005GL024191/2005GL024191.pdf
Bangs, N.L., Gulick, S. and Shipley, T.H., 2006, Seamount subduction erosion in the Nankai Trough and its potential impact on the seismogenic zone, Geology, vol. 34, p. 701–704, DOI: 10.1130/G22451.1.
Seismic Acquisition Parameters
Receiver Type
Hydrophone:Streamer
Source Type
AirGun:Bolt1500
Acquisition System Name
Syntrack 480-24
Acquisition System Type
Seismic Navigation System
Differential GPS with a final post-cruise UKOOA 90 P1 navigation format (EW9907.v19.ukooa; 932 MB uncompressed; 290 MB compressed). This format includes all the important data associated with the navigation systems; antennas positions; cable compasses and positions for each source of the approximately 150;000 shots and each of the 240 channels. In addition there is the 'standard' *.nav file of just shot locations for the cruise and by line.
Survey Datum
WGS84
Source to Near Channel (meters)
188
Antenna to Source (meters)
56
Number of Channels Recorded
240
Number of Cables
Number of Channels Each Cable
Channel Length (meters)
25
Cable Length (meters)
Cable Spacing (meters)
Near Channel Number
Cable Receiver Depth (meters)
8
Cable Receiver Depth Recorded
Number Source Arrays
FlipFlop Shooting
Source Array Separation (meters)
Source Volume (cubic inches)
4276
Source Pressure (bars)
138
Source Number
14
Source Depth (meters)
6
Processing System
SIOSEIS; Geovecteur
Shot Control
distance
Shot Interval (meters)
50
Sample Interval (microseconds)
2000
Record Length (seconds)
12
Compass Birds
Tail Buoy Positioning
Recording Delay
Comments
General Processing Description Shipboard pre-processing: The 3490-type field tapes with 2-ms sample interval were anti-alias filtered and resampled to 4 ms on board ship. The field reels were combined into individual SEGY files spanning an entire line. Numerous parts of lines were re-shot for a variety of reasons and given line name suffixes, A, B and C. Two-dimensional stacks and migrations were created on board as part of the quality control by the University of Hawaii. The basic data processing used Pardigm's Focus software. Conventional binning and initial post-stack time migrations were completed in 2001. Two processing reports are available, though both were written as internal documents to outline the processing efforts. The first discusses preliminary processing and several experiments with different binning parameters. The second explains the final binning used for the post stack migration and the background leading up to the pre-stack time migration. Both reports (ew9907.processing1.pdf and ew9907.processing2.pdf) are very large files.
