Special Issue: Special Section for the 2004 off the Kii peninsula earthquakes (2)
The September 5, 2004 off the Kii Peninsula earthquakes as a composition of bending and collision
Earth, Planets and Space volume 57, pages 327–332 (2005)
The 2004 off the Kii Peninsula earthquakes ruptured the subducting Philippine Sea plate near the axis of the Nankai Trough. A series of major events (the fore- and mainshocks with Mw>7) showed very peculiar rupture characteristics. The depth extent of the foreshock is around 12–23 km below the sea surface; in contrast, that of the mainshock is around 7–17 km, shallower and closer to the upper surface of the plate than the foreshock. The focal mechanism of the foreshock is almost pure reverse faulting, with a P-axis directing roughly N-S, that is rotated clockwise by 20–25° from the trough normal. In contrast, the mainshock involved a significant component of strike-slip faulting, with a similar P-axis. The OBS survey revealed a double layer of the aftershock activity and the upper NW trending layer contains aftershocks with strike-slip focal mechanisms. These features indicate that the compressional and tensional stress domains due to bending are significantly modified by tectonic stress disturbance and produced the fore- and mainshock ruptures deviated from simple reverse and normal faulting. I show that a supposed N-S compressional stress, which might be produced by the collision south of the Izu Peninsula, can rotate the principal stress axes and change the stress type, which are consistent with the P-axes of these events and the strike-slip component for the mainshock. The complex rupture mode of the mainshock might have been produced by superposition of the depth-dependent tensional bending stress in the upper half of the lithosphere and the collisional stress. This collisional stress should be comparable to the bending stresses in magnitude, which is much larger than the stress perturbation caused by nearby interplate locking.
Aoki, H., Geometry of the subducted Philippine Sea plate and its continuity, Rep. Tono Res. Inst. Earthquake Sci., Seq. No. 12, 43–51, 2003 (in Japanese).
Baba, T., P. R. Cummins, and T. Hori, Compound fault rupture during the 2004 off the Kii Peninsula earthquake (M 7.4) inferred from highly resolved coseismic sea-surface deformation, Earth Planets Space, 57, 167–172, 2005.
Caldwell, J. G., W. F. Haxby, D. E. Karig, and D. L. Turcotte, On the applicability of a universal elastic trench profile, Earth Planet. Sci. Lett., 31, 239–246, 1976.
Chapple, W. M. and D. W. Forsyth, Earthquakes and bending of plates at trenches, J. Geophys. Res., 84, 6729–6749, 1979.
Christensen, D. H. and L. J. Ruff, Seismic coupling and outer-rise earthquakes, J. Geophys. Res., 93, 13421–13444, 1988.
Davies, G. F., On the emergence of plate tectonics, Geology, 20, 963–966, 1992.
Fukuyama, E., A. Kubo, H. Kawai, and K. Nonomura, Seismic remote monitoring of stress field, Earth Planets Space, 53, 1021–1026, 2001.
Hara, T., Change of the source mechanism of the mainshock of the 2004 off the Kii Peninsula earthquakes inferred from long period body wave data, Earth Planets Space, 57, 179–183, 2005.
Ito, Y., T. Matsumoto, H. Kimura, H. Matsubayashi, K. Obara, and S. Sekiguchi, Spatial distribution of centroid moment tensor solutions for the 2004 off Kii peninsula earthquakes, Earth Planets Space, 57, 351–356, 2005.
Japan Meteorological Agency (JMA), http://www.jishin.go.jp/main/chousa/04oct_kiihantou/p03.htm, 2004.
Lay, T., D. H. Christensen, L. Astiz, and H. Kanamori, Temporal variation of large intraplate earthquakes in coupled subduction zones, Phys. Earth Planet. Inter., 54, 258–312, 1989.
Miyoshi, T. and K. Ishibashi, Geometry of the seismic Philippine Sea slab beneath the region from Ise Bay to western Shikoku, Southwest Japan, Jisin, 57, 139–152, 2004 (in Japanese).
Nagai, R., M. Kikuchi, and Y. Yamanaka, Comparative study on the source processes of reccurrent large earthquakes in Sanriku-oki region: the 1968 Tokachi-oki earthquake and the 1994 Sanriku-oki earthquake, Jisin, 54, 267–280, 2001 (in Japanese).
National Research Institute for Earth Science and Disaster Prevension, http://www.hinet.bosai.go.jp/topics/se-off-kii0409/, 2004.
Noguchi, S., Geometry of the Philippine Sea slab and the convergent tectonics in the Tokai District, Japan, Jisin, 49, 295–325, 1996 (in Japanese).
Okino, K., Y. Shimakawa, and S. Nagano, Evolution of the Shikoku Basin, J. Geomag. Geoelectr., 46, 463–479, 1994.
Parsons, B. and J. G. Sclater, An analysis of the variation of ocean floor bathymentry and heat flow with age, J. Geophys. Res., 82, 803–827, 1977.
Parsons, B. and F. M. Richter, A relation between the driving force and geoid anomaly associated with mid-oceanic ridges, Earth Planet. Sci. Lett., 51, 445–450, 1980.
Sakai, S., M. Shinohara, T. Yamada, H. Hagiwara, T. Kanazawa, K. Obana, S. Kodaira, M. Kinoshita, and Y. Kaneda, Temporary aftershock observation using OBS of the 2004 Kii-hanto-nanto-oki earthquakes, A talk given at the monthly meeting of the Earthq. Res. Inst., Univ. Tokyo, Oct. 16, 2004, 2004.
Satake, K., T. Baba, K. Hirata, S. Iwasaki, T. Kato, S. Koshimura, J. Takenaka, and Y. Terada, Tsunami source of the 2004 off the Kii Peninsula earthquakes inferred from offshore tsunami and coastal tide gauges, Earth Planets Space, 57, 173–178, 2005.
Seno, T., Focal mechanism and depth of the 1971 January 3 earthquake (M5.5) which occurred near the Zenisu Ridge off central Honshu—Implications for the Philippine Sea palte thickness at the western margin of the Izu Ridge, Jisin, 40, 629–632, 1987 (in Japanese).
Seno, T., Syntheses of the regional stress fields of the Japanese islands, The Island Arc, 8, 66–79, 1999.
Seno, T., Why the Philippine Sea plate moves as it does, J. Geol. Soc. Phil., 55, 105–117, 2000.
Seno, T., Collision vs. subduction: the importance of slab dehydration, in The Seismogenic Zone of Subduction Thrust Faults, edited by T. Dixon and J. C. Moore, Columbia Univ Press, 2005a (in press).
Seno, T., Izu detachment hypothesis: A proposal of a unified cause for the Miyake-Kozu event and the Tokai slow event, Earth Planets Space, 2005b (in press).
Seno, T. and Y. Yamanaka, Double seismic zones, compressional deep trench-outer rise events and superplumes, in Subduction Top to Bottom, edited by G. E. Bebout, D. W. Scholl, S. H. Kirby, and J. P. Platt, Geophys. Monogr, AGU, Washington D. C., 96, pp. 347–355, 1996.
Seno, T. and Y. Yamanaka, Arc stresses determined by slabs: Implications for mechanisms of back-arc spreading, Geophys. Res. Lett., 25, 3227–3230, 1998.
Seno. T., S. Stein, and A. E. Gripp, A model for the motion of the Philippine Sea plate consistent with NUVEL-1 and geological data, J. Geophys. Res., 98, 17941–17948, 1993.
Seno, T., T. Sakurai, and S. Stein, Can the Okhotsk plate be discriminated from the North American plate?, J. Geophys. Res., 101, 11305–11315, 1996.
Seno, T., D. Zhao, Y. Kobayashi, and M. Nakamura, Dehydration in serpentinized slab mantle: Seismic evidence from southwest Japan, Earth Planets Space, 53, 861–871, 2001.
Taira, A., K. T. Pickering, B. F. Windley, and W. Soh, Accretion of Japanese island arcs and implications for the origin of Archean greenstone belts, Tectonics, 11, 1224–1244, 1992.
Ukawa, M., Lateral stretching of the Philippine sea plate subducting along the Nankai-Suruga Trough, Tectonics, 1, 543–571, 1982.
Wang, K. and J. He, Mechanics of low-stress forearcs: Nankai and Cascadia, J. Geophys. Res., 104, 15191–15205, 1999.
Wiens, D. A. and S. Stein, Age dependence of oceanic intraplate seismicity and implications for lithospheric evolution, J. Geophys. Res., 88, 6455–6468, 1983.
Yamanaka, Y., http://www.eri.u-tokyo.ac.jp/sanchu/Seismo_Note/2004/EIC152.html, 2004.
Yamasaki, T. and T. Seno, Double seismic zones and dehydration embrittlement, J. Geophys. Res., 108(B4), 2212, doi:10.1029/2002JB001918, 2003.
Yoshioka, S. and Y. Ito, Lateral variations of effective elastic thickness of the subducting Phillippine Sea plate along the Nankai trough, Earth Planets Space, 53, 261–273, 2001.
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Seno, T. The September 5, 2004 off the Kii Peninsula earthquakes as a composition of bending and collision. Earth Planet Sp 57, 327–332 (2005). https://doi.org/10.1186/BF03352571