Gulick, Sean P. S.; Bangs, Nathan L. B. (2005): Negative polarity at the frontal-thrust; is free gas the culprit? Insights from Nankai accretionary prism off Cape Muroto using seismic-logging integration. Texas A&M University, Ocean Drilling Program, College Station, TX, United States, In: Moore, Gregory F., Taira, Asahiko, Klaus, Adam, Becker, Keir, Becker, Luann, Boeckel, Babette, Cragg, Barry A., Dean, P. Allison, Fergusson, Christopher L., Henry, Pierre, Hirano, Satoshi, Hisamitsu, Toshio, Hunze, Sabine, Kastner, Miriam, Maltman, Alex J., Morgan, Julia K., Murakami, Yuki, Saffer, Demian M., Sanchez-Gomez, Mario, Screaton, Elizabeth J., Smith, David C., Spivack, Arthur J., Steurer, Joan F., Tobin, Harold J., Ujiie, Kohtaro, Underwood, Michael B., Wilson, Moyra E. J., Mikada, Hitoshi, Moore, J. Casey, Austin, Gary L., Bangs, Nathan L. B., Bourlange, Sylvain, Broilliard, Julien, Brueckmann, Warner, Corn, Ernest Ray, Davis, Earl E., Flemings, Peter B., Goldberg, David S., Gulick, Sean P. S., Hansen, Martin Bak, Hayward, Nathan, Hills, Denise J., Ienaga, Masanori, Ishiguro, Hiroyasu, Kinoshita, Masataka, Macdonald, Robert D., McNeill, Lisa, Obana, Shinichi, Hong, Ong Swee, Peacock, Sheila, Pettigrew, Thomas L., Saito, Saneatsu, Sawa, Takao, Thaiprasert, Nophawit, Tsurumi, Hikaru, Proceedings of the Ocean Drilling Program; scientific results; deformation and fluid flow processes in the Nankai Trough accretionary prism; coring, logging while drilling and advanced CORKs covering Legs 190 to 196 of the cruises of the drilling vessel JOIDES Resolution; Sydney, Australia, to Yokohama, Japan, Sites 1173-1178, 23 May-16 July 2000; and Keelung, Taiwan, to Kochi, Japan, Sites 808-1173, 2 May-1 July 2001, 190/196, georefid:2005-060951

Within the Nankai accretionary prism off Cape Muroto, Japan, the frontal thrust and thrusts within the imbricate thrust zone show consistent negative polarity fault plane reflections that decrease in amplitude landward. However, the protothrust faults lack a fault plane reflection in three-dimensional seismic data. Differences in velocity and density of the overthrust sections at the proto- and frontal thrusts vs. their underthrust sections is insufficient by an order of magnitude to explain the presence of the fault plane reflection at the frontal thrust. Forward modeling with synthetic seismograms shows that the best match of the logging-while-drilling data with the seismic data at Site 808 is a approximately 1-m-thick low velocity (1800 m/s) and low density (1.25 g/cm (super 3) ) fault zone; however, a wider zone with higher velocity and/or densities is also consistent with the seismic data. High resistivity values across the frontal thrust suggest that the presence of free gas generates the negative polarity reflection. Correlation of the shallowest high-amplitude bright spots along the numerous fault plane reflections from the imbricate thrust zone with the gas hydrate-related bottom-simulating reflector suggests that free gas migrates up the fault zone to pool at the base of the hydrate stability zone and potentially increase concentrations of hydrate above the base of the hydrate stability field. These results suggest that free gas may play a role in generating negative polarity fault plane reflections elsewhere.
West: 134.0000 East: 136.0000 North: 34.0000 South: 32.0000
Expedition: 131
Expedition: 190
Expedition: 196
Supplemental Information:
Available only on CD-ROM in PDF format and on the Web in PDF or HTML
Data access:
Provider: SEDIS Publication Catalogue
Data set link: (c.f. for more detailed metadata)
Data download: application/pdf
This metadata in ISO19139 XML format