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Seventeenth-century uplift in eastern Hokkaido, JapanU. S. Geological Survey at University of Washington, Seattle, Washington 98195-1310, USA atwatergu.washington.edu
Institute of Geoscience, GSJ-AIST, Tsukuba 305-8567, Japan
Department of Geology, Humboldt State University, Arcata, California 95521, USA
Department of Geography, University of Tokyo, Faculty of Science Building #5, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
Department of Earth and Planetary Sciences, Kyushu University, Fukuoka 812-8581, Japan
Faculty of Education, Ehime University, Matsuyama 790-8577, Japan
Department of Geology, Humboldt State University, Arcata, California 95521, USA
Department of Geology, Kent State University, Kent, Ohio 44242, USA
Geological Survey of Japan, AIST, Tsukuba 305-8567, Japan
1nstitute of Seismology and Volcanology, Hokkaido University, Sapporo 060-0810, Japan
Geographical Survey Institute, Tsukuba, Ibaraki 305-0811, Japan
2-11-13-201, Minami-Senzoku, Ota-ku, Tokyo 145-0063, Japan
Research Center for Earthquake Prediction, Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
Geological Survey of Japan, AIST, Tsukuba 305-8567, Japan Shores of eastern Hokkaido rose by perhaps I m a few centuries ago. The uplifted area extended at least 50km along the southern Kuril Trench. It included the estuaries Akkeshi-ko and Hichirippu, on the Pacific coast, and Furen-ko and Onneto, which open to the Okhotsk Sea. At each estuary, intertidal and subtidal flats rose with respect to tide level; wetland plants colonized the emerging land; and peaty wetland deposits thereby covered mud and sand of the former flats. Previous work at Akkeshi-ko and Onneto showed that such emergence occurred at least three times in the past 3000 years. Volcanic-ash layers date the youngest emergence to the seventeenth century AD. New evidence from Akkeshi-ko, Hichirippu and Furen-ko clarifies the age and amount of this youngest emergence. Much of it probably dates from the century's middle decades. Some of the newly emerged land remained above high tides into the middle of the eighteenth century or later. The emergence in the last half of the seventeenth century probably exceeded 0.5 m (inferred from stratigraphy and diatom palaeoecology) without far exceeding I m (estimated by comparing seventeenth-and eighteenth-century descriptions of Akkeshi-ko). The stratigraphy and palaeoecology of the emergence are better explained by tectonic uplift than by bay-mouth blockage, tidal-flat accretion or sea-level fall. Eastern Hokkaido needs occasional uplift, moreover, to help reconcile its raised marine terraces with its chronic twentieth-century subsidence. Because it took place above forearc mantle, eastern Hokkaido's seventeenth-century uplift probably lacks analogy with coseismic uplift that occurs above typical plate-boundary ruptures at subduction zones.
Key Words: Uplift • estuaries • sea level • subduction • palaeoecology • palaeoseismology • Japan
The Holocene, Vol. 14, No. 4,
487-501 (2004) This article has been cited by other articles:
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