Seismic imaging for an ocean drilling site survey and its verification in the Izu rear arc

Figures & data

Fig. 1.  Bathymetry of the northern Izu-Ogasawara arc showing the rear-arc drilling site U1437 (light blue star). Bold blue dotted lines show four en-echelon chains of back-arc seamounts extending obliquely in an ENE–WSW direction, from the back-arc knolls zone to the Shikoku Basin. Red and yellow lines indicate the survey lines used in this study.

Table 1.  Seismic survey equipment and data acquisition parameters.

Survey lines	IBM3a, IBM3b, IBM3d, IBM3e, IBM3f	IBr5	NE3, NE4, NE5, NE6, NE7, NW4, NW5, NW6
Vessel	Kaiyo	Kairei	Kairei
Cruise	KY06–14	KR07–09	KR08–04
Gun type	G-gun	LL gun	Annular port gun
Shot interval	25 m	50 m (MCS), 200 m (OBS)	50 m
Volume of air gun	600 cu.in.	12000 cu.in.	7800 cu.in.
Gun depth	5 m	10 m	6 m
CDP fold	6	51	55.5
Streamer length	450 m	5100 m	5500 m
Record length	8 s	18 s	15 s
Sampling interval	0.001 s	0.004 s	0.001 s
Number of channel	12	204	444
Cable depth	15 m	15 m	8 m

Fig. 2.  Maps showing the site survey lines and detailed bathymetry around the Izu rear-arc drilling site U1437 (light blue star). (a) Pre-site survey lines. The numbers with white boxes in Figure 2a show the ⁴⁰Ar–³⁹Ar ages (Ma) of dredged samples obtained by Ishizuka et al. (2003). (b) High-resolution survey lines.

Fig. 3.  Seismic reflection profiles and interpretations obtained in the pre-site survey: (a) line IBM3e; (b) expanded interpretation of line IBM3e; (c) line IBM3d; (d) expanded interpretation of line IBM3d. Dotted boxes show the expanded areas around the drilling site U1437, indicated by arrows. Ages were obtained from dredged sample by Ishizuka et al. (2003).

Fig. 4.  High-resolution seismic reflection profiles with interpretations: (a) line NE5 and (b) line NW5. Arrows with white rectangular boxes show the drillhole U1437.

Fig. 5.  Seismic profiles of line IBr5 which runs east from the Manji seamount chains to the Empo seamount chains: (a) Detailed bathymetry map of the Shikoku Basin and en-echelon arrangements around the drilling site U1437, indicated by light blue star. (b) Final velocity model modified from Takahashi et al. (2015). (c) Depth-converted seismic reflection profile, and expanded time-migrated profiles with our interpretation. The drilling site U1437 is also shown. (d) Interpretations of IBr5 from seismic reflection profiles and velocity model. The green rectangular box shows the location of drillhole U1437. Blue and red dashed lines indicate the velocity contours of 5 km/s and 6 km/s traced from (b), which are interpreted as the depth to igneous basement (upper crust) and middle crust, respectively.

Fig. 6.  Lithologic columns at the drilling site U1437: (a) Seismic units interpreted before drilling; (b) geological column obtained from drilling and coring (Expedition 350 Scientists, 2014); (c) depth converted seismic reflection profile with the interpretation of line NW5 around the drilling site U1437, calculated from the time-depth relationship derived from vertical seismic profiling in the drillhole (modified from Tamura et al., 2015); (d) detailed depth converted seismic reflection profile of line IBr5 around the drilling site U1437.

Fig. 7.  Thickness variations in two-way traveltime estimated from the grid of site surveys around Site U1437: (a) thickness of unit I; (b) thickness from unit II – IV; (c) thickness of unit V; (d) thickness of unit VI. The yellow star shows the location of Site U1437.

Fig. 8.  Expanded profiles around the Site U1437 showing the nearest CDP traces to the site. These traces were used to calculate the coherence between the lines, shown in the coherence spectra: (a) 2.8–3.8 s window (unit I–III); (b) 3.8–4.8 s window (unit III–VII).

Ishizuka, O., Uto, K., and Yuasa, M., 2003, Volcanic history of the back-arc region of the Izu-Bonin (Ogasawara) arc, in R. D. Larter, and P. T. Leat, eds., Tectonic and magmatic processes: Geological Society Special Publication, 219(1), 187–205.

 Google Scholar

Takahashi N. Kodaira S. Sato T. Yamashita M. Kaiho Y. Miura S. No T. Takizawa K. Noguchi N. Shimomura N. Kaneda Y. 2015 Velocity structure of the Izu-Ogasawara island arc: The Journal of Geography [Chigaku Zasshi], 124 813 827 10.5026/jgeography.124.813

 Web of Science ®Google Scholar

Expedition 350 Scientists, 2014, Izu-Bonin-Mariana rear arc: the missing half of the subduction factory: International Ocean Discovery Program Preliminary Report, 350. Available at: <http://dx.doi.org/10.14379/iodp.pr.350.2014>

 Google Scholar

Tamura, Y., Busby, C. J., Blum, P., Guèrin, G., Andrews, G. D. M., Barker, A. K., Berger, J. L. R., Bongiolo, E. M., Bordiga, M., DeBari, S. M., Gill, J. B., Hamelin, C., Jia, J., John, E. H., Jonas, A.-S., Jutzeler, M., Kars, M. A. C., Kita, Z. A., Konrad, K., Mahoney, S. H., Martini, M., Miyazaki, T., Musgrave, R. J., Nascimento, D. B., Nichols, A. R. L., Ribeiro, J. M., Sato, T., Schindlbeck, J. C., Schmitt, A. K., Straub, S. M., Vautravers, M. J., and Yang, Y., 2015, Site U1437, in Y. Tamura, C. J. Busby, P. Blum, and the Expedition 350 Scientists, eds., Proceedings of the International Ocean Discovery Program, Expedition 350: Izu-Bonin-Mariana Rear Arc: International Ocean Discovery Program, 1–142.

 Google Scholar