Western Nankai Trough seismogenic zone; results from a wide-angle ocean bottom seismic survey

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doi: 10.1029/1999JB900394
Author(s): Kodaira, Shuichi; Takahashi, Narumi; Park, Jin-Oh; Mochizuki, Kimihiro; Shinohara, Masanao; Kimura, Shozo
Author Affiliation(s): Primary:
Japan Marine Science and Technology Center, Yokosuka, Japan
University of Tokyo, Japan
Chiba University, Japan
Kochi University, Japan
Volume Title: Journal of Geophysical Research
Source: Journal of Geophysical Research, 105(B3), p.5887-5905. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0148-0227
Note: In English. 56 refs.; illus., incl. geol. sketch map, sects.
Summary: The Nankai Trough, southwestern Japan, is recognized as a vigorous seismogenic zone with well-studied historic earthquakes. This paper presents results of a wide-angle ocean bottom seismographs (OBS) study at the western Nankai Trough seismogenic zone. The OBS data used were acquired on a profile (250 km long) across the presumed coseismic slip zone of the 1946 Nankaido earthquake (Ms=8.2). The main purpose of the seismic study is to obtain an entire crustal cross section of the seismogenic zone for the 1946 earthquake. The crustal model is characterized by a gentle sloping of subducting oceanic crust and thick overlying sedimentary wedge. P wave seismic velocities of the subducting oceanic crust show normal oceanic crustal velocities (Vp=5.0-5.6 km/s and 6.6-6.8 km/s in oceanic layers 2 and 3, respectively). The maximum thickness of the sedimentary wedge is 9 km at 70 km from the trough axis with Vp=3.4-4.6 km/s in the deeper part. The subducting oceanic crust traced down to 25 km depth shows that the subduction angle becomes steeper landward: 3.2°and 7.2° at 0-50 km and 50-100 km from the trough axis, respectively. The oceanic crust is smooth to the hypocenter zone, down to 40 km depth beneath Shikoku Island. Our crustal model shows that the downdip limit of the coseismic slip area does not extend to the deep end of the oceanic crust-island arc crust contact zone. Even though there is large uncertainty about the seaward limit of the coseismic slip zone, the crustal model clearly indicates that the updip limit of the coseismic slip zone extends beneath the young accretionary prism. Copyright 2000 by the American Geophysical Union.
Year of Publication: 2000
Research Program: ODP Ocean Drilling Program
Key Words: 18 Geophysics, Solid-Earth; 20 Geophysics, Applied; Body waves; Coseismic processes; Earthquakes; Elastic waves; Faults; Focus; Geophysical methods; Geophysical surveys; Geotraverses; Leg 131; Marine methods; Nankai Trough; Nankaido earthquake 1946; North Pacific; Northwest Pacific; Ocean Drilling Program; P-waves; Pacific Ocean; Plate tectonics; Seismic methods; Seismic waves; Strike-slip faults; Subduction; Surveys; West Pacific; Wide-angle methods
Coordinates: N310000 N340000 E1550000 E1200000
Record ID: 2000039230
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