A high-resolution 3D seismic reflection survey and prestack depth imaging in the Nankai Trough off southeast Kii Peninsula

Author(s): Park, Jin-Oh; Tsuru, Tetsuro; No, Tetsuo; Takizawa, Kaoru; Sato, So; Kameda, Yoshiyuki
Author Affiliation(s): Primary:
University of Tokyo, Ocean Research Institute, Tokyo, Japan
Other:
Japan Agency for Marine-Earth Science and Technology, Japan
JGI, Japan
Volume Title: Butsuri-Tansa Geophysical Exploration
Source: Butsuri-Tansa = Geophysical Exploration, 61(3), p.231-241. Publisher: Society of Exploration Geophysicists of Japan, Tokyo, Japan. ISSN: 0912-7984 CODEN: BTANAF
Note: In Japanese with English summary. 17 refs.; illus., incl. sects., 1 table, sketch map
Summary: In late 2007, the IODP NanTroSEIZE project will commence drilling into the seismogenic portion of the megathrust along which the 1944 Tonankai earthquake (M = 8.1) has occurred off the Kii Peninsula, southwest Japan. In order to figure out high-resolution structure and physical property of the subducting Philippine Sea Plate (PSP) consisting of oceanic crust and incoming sedimentary strata, we have performed a high-resolution, three-dimensional (3D) multi-channel seismic (MCS) reflection survey (KR06-02 cruise) in the Nankai Trough off Kii Peninsula using R/V Kairei of the Japan Agency for Marine-Earth Science and Technology in March, 2006. This Kairei 3D survey area covers three drilling sites of the NanTroSEIZE. For the high-resolution 3D MCS survey, we used a ∼5-km, 204-channel streamer and ∼100 m separated dual source, each of which is composed of two G-guns plus a GI-gun. Flip-flop shooting with 30 m interval yields ∼50 m separated two CMP lines, resulting in 3.5×52 km 3D seismic volume. Recording length with 1 msec sampling interval is 10 sec. Depths of source and streamer cable are 5 m and 8 m, respectively. We used REFLEX system for onboard real-time 3D QC binning as well as SPECTRA navigation system. For the 3D data, we applied bandpass filter, amplitude recovery, deconvolution, multiple suppression, 3D geometry, flexible binning, and NMO velocity analysis. Then, we have constructed and updated interval velocity volume model for 3D prestack depth migration (PSDM) following 3D prestack time migration using those CMP bin gathers. A velocity uncertainty test demonstrates that the final 3D PSDM velocity has a ∼5% maximum velocity uncertainty at ∼6 km depth. Final 3D PSDM result shows high-resolution seismic images of three Miocene to Pliocene Shikoku Basin sedimentary units (Units A, B, and C) including three remarkable turbidites. The oceanic crust of the subducting Philippine Sea Plate underthrusts the overlying the accretionary prism, and is traceable over the entire inlines. In particular, Unit C beneath the trough turbidite fill shows unusual increase of thickness and anticline structure, which have never been reported in the Nankai Trough. We observe a noticeable, strong reflector (Reflector-R) immediately beneath the anticline structure, which is located at almost midst level of the Unit C. We interpret that both the anticline structure and thickness increase might be resulted from duplication of stratigraphic section following oblique slip up the sidewall ramp.
Year of Publication: 2008
Research Program: IODP Integrated Ocean Drilling Program
IODP2 International Ocean Discovery Program
Key Words: 19 Geophysics, Seismology; 20 Geophysics, Applied; Asia; Depth; Earthquakes; Far East; Faults; Geophysical methods; Geophysical surveys; High-resolution methods; Honshu; Imagery; Integrated Ocean Drilling Program; International Ocean Discovery Program; Japan; Kii Peninsula; Magnitude; NanTroSEIZE; Nankai Trough; North Pacific; Northwest Pacific; Oblique-slip faults; Pacific Ocean; Philippine Sea Plate; Plate tectonics; Prestack migration; Reflection methods; Seismic methods; Seismic migration; Seismicity; Surveys; Three-dimensional models; Tonankai earthquake 1944; West Pacific
Coordinates: N323000 N333000 E1373000 E1360000
Record ID: 2009040286
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