Field survey report on tsunami disasters caused by the 1993 Southwest Hokkaido earthquake
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Detailed field work at Okushiri Island and along the southwest coast of Hokkaido has revealed quantitatively (1) the advancing direction of tsunami on land, (2) the true tsunami height (i.e., height of tsunami, excluding its splashes, as measured from the ground) and (3) the flow velocity of tsunami on land, in heavily damaged areas. When a Japanese wooden house is swept away by tsunami, bolts that tie the house to its concrete foundation resist until the last moment and become bent towards the direction of the house being carried away. The orientations of more than 850 of those bent bolts and iron pipes (all that can be measured, mostly at Okushiri Island) and fell-down direction of about 400 trees clearly display how tsunami behaved on land and caused serious damage at various places. The true tsunami height was estimated by using several indicators, such as broken tree twigs and a window pane. The flow velocity of tsunami on land was determined by estimating the hydrodynamic force exerted on a bent handrail and a bent-down guardrail by the tsunami throughin situ strength tests.
Contrary to the wide-spread recognition after the tsunami hazard, our results clearly indicate that only a few residential areas (i.e., Monai, eastern Hamatsumae, and a small portion at northern Aonae, all on Okushiri Island) were hit by a huge tsunami, with true heights reaching 10 m. Southern Aonae was completely swept away by tsunami that came directly from the focal region immediately to the west. The true tsunami height over the western sea wall of southern Aonae was estimated as 3 to 4 m. Northern Aonae also suffered severe damage due to tsunami that invaded from the corner zone of the sand dune (8 m high) and tide embankment at the northern end of the Aonae Harbor. This corner apparently acted as a tsunami amplifier, and tide embankment or breakwater can be quite dangerous when tsunami advances towards the corner it makes with the coast. The nearly complete devastation of Inaho at the northern end of Okushiri Island underscored the danger of tsunami whose propagation direction is parallel to the coast, since such tsunami waves tend to be amplified and tide embankment or breakwater is constructed low towards the coast at many harbors or fishing ports. Tsunami waves mostly of 2 to 4 m in true height swept away Hamatsumae on the southeast site of Okushiri Island where there were no coastal structures. Coastal structures were effective in reducing tsunami hazard at many sites. The maximum flow velocity at northern Aonae was estimated as 10 to 18 m/s (Tsutsumi et al., 1994), and such a high on-land velocity of tsunami near shore is probably due to the rapid shallowing of the deep sea near the epicentral region towards Okushiri Island. If the advancing direction, true height, and flow velocity of tsunami can be predicted by future analyses of tsunami generation and progagation, the analyses will be a powerful tool for future assessment of tsunami disasters, including the identification of blind spots in the tsunami hazard reduction.
- Abe, K. (1994),An Island Effect on the Propagation of Tsunami due to the Southwest Hokkaido Earthquake (in Japanese), Earth Monthly, Suppl.7, 185–191.
- Curray, J. R. (1956),The Analysis of Two-dimensional Orientation Data, J. Geol.64, 117–131.
- Goto, A., Takahashi, H., Utsugi, M., Ono, S., Nishida, Y., Ohshima, H., Kasahara, M., Takenaka, H., andSaita, T. (1994),Tsunami due to the Southwest Hokkaido Earthquake: From Otaru to Reibun Island (in Japanese), Earth Monthly, Suppl.7, 153–158.
- Kikuchi, M. (1994),The Nicaraguan Tsunamigenic Earthquake as Recorded in Wide-band Seismometers (in Japanese), Earth Monthly16, 116–122.
- Kuge, K., Kikuchi, M., andZhang, J. (1994),Complex Source Processes of the Southwest Hokkaido Earthquake (July 12, 1993) as Revealed from Far-field Body and Surface Waves (in Japanese), Earth Monthly, Suppl.7, 21–28.
- Imamura, F., Takahashi, T., andTakahashi T. (1994),Is the Earthquake Fault of the Southwest Hokkaido Earthquake Dipping to West, or to the East?: An Inference from Tsunami Data (in Japanese), Earth Monthly, Suppl.7, 179–184.
- Matsutomi, H., andShuto, N. (1994),The Southwest Hokkaido Earthquake Tsunami near Okushiri Island and its Velocity on Land (in Japanese), Earth Monthly, Suppl.7, 132–138.
- Mogi, K.,Earthquake Prediction (Academic Press 1985), 355 pp.
- Nakanishi, I., andKikuchi, M. (1993),Characteristics of earthquake and induced groundmotion (in Japanese). InSpecial Issue on the 1993 Southwest Hokkaido Earthquake, Japan Society for Earthquake Engineering Promotion, NEWS133, 1–5.
- Sato, H., Shimamoto, T., Tsutsumi A., andKawamoto, E. (1994),Onshore Tsunami Deposits Caused by the 1993 Southwest Hokkaido Earthquake and the 1983 Japan Sea Earthquake, Pure and Appl. Geophys., this issue.
- Satake, K., andTanioka, Y. (1994),Tsunami Generation of the 1993 Hokkaido Nansei-oki Earthquake, Pure and Appl. Geophys., this issue.
- Shimamoto, T., Tsutsumi, A., Kawamoto, E., Miyawaki, M., andSato, H. (1994),Tsunami Disasters due to the Southwest Hokkaido Earthquake and Lessons for Tsunami Disaster Prevention (in Japanese), Earth Monthly, Suppl.7, 219–231.
- Shimamoto, T., Tsutsumi, A., Kawamoto, E., Miyawaki, M., andSato, H. (in preparation),Advancing Direction and True Tsunami Height of Southwest Hokkaido Tsunami and their Implications for the Prevention of Future Tsunami Disasters (in Japanese), to be submitted to Bull. Earthquake Res. Institute.
- Shuto, N. (1993),Damage due to tsunami (in Japanese). InSpecial Issue on the 1993 Southwest Hokkaido Earthquake, Japan Society for Earthquake Engineering Promotion NEWS133, 21–24.
- Takahashi, T., Ortiz, M., Takahashi, T., andShuto, N. (1994),Initial Profile of the Hokkaido Nansei-oki Earthquake Tsunami for a Better Simulation (in Japanese), Abstracts for Japan Earth and Planetary Science Joint Meeting, p. 264.
- Tanioka, Y., Satake, K., andRuff, L. (in review),Total Analysis of the 1993 Hokkaido Nansei-oki Earthquake Using Seismic Wave, Tsunami, and Geodetic Data, Geophys. Res. Lett.
- Tsuji, Y., Kato, K., Arai, K., Han, S., andYamanaka, Y. (1994a),Characteristics of Tsunami due to the Southwest Hokkaido Earthquake (in Japanese), Earth Monthly, Suppl.7, 110–122.
- Tsuji, Y., Kato, K., Arai, K., Arai, K., andUeda, K. (1994b),Run-up Height Distribution of Tsunami due to the Southwest Hokkaido Earthquake along Coast of Southwest Japan (in Japanese), Earth Monthly, Suppl.7, 110–122.
- Tsutsumi, A., Shimamoto, T., Miyawaki, M., Sato, H., andKawamoto, E. (1993),Subsidance of Okushiri Island during the 1993 Southwest Hokkaido Earthquake (abstract in Japanese), Abstract for the Seismological Society of Japan Meeting,2, 62.
- Tsutsumi, A., Shimamoto, T., Kawamoto, E., andLogan, J. M. (1994),Estimation of Near-shore Velocity of the Southwest Hokkaido Earthquake Tsunami (in Japanese), Earth Monthly, Suppl.7, 166–172.
- Field survey report on tsunami disasters caused by the 1993 Southwest Hokkaido earthquake
pure and applied geophysics
Volume 144, Issue 3-4 , pp 665-691
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