Seventeenth-century uplift in eastern Hokkaido, Japan

Abstract

Shores of eastern Hokkaido rose by perhaps 1 m a few centuries ago. The uplifted area extended at least 50 km along the southern Kuril Trench. It included the estuaries Akkeshi-ko and Hichirippu, on the Pacific coast, and Fūren-ko and Onnetō, 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 Onnetō 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 Fūren-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 1 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.

The Role of Holocene Relative Sea-Level Change in Preserving Records of Subduction Zone Earthquakes

“…The tide gauge records in eastern Hokkaido, northern Japan, display submergence of 8-10 mm/year over the last ∼100 years [81]. This pronounced subsidence over the twentieth century has been ascribed to interseismic strain accumulation that has not been reversed by recent earthquakes [81]. Infrequent postseismic uplift may help reconcile eastern Hokkaido's twentieth century submergence with its stratigraphic evidence of long-term RSL fall during the Holocene [81,93].…”

“…h Age ranges for four [80,93] and six [15] instances of postseismic uplift in eastern Hokkaido (Onnetoh and Kiritappu) change between a tidal flat mud and a freshwater marsh, signaling at least 1 m of slow, postseismic uplift following earthquakes larger than any in the region's written history [91,93]. The tide gauge records in eastern Hokkaido, northern Japan, display submergence of 8-10 mm/year over the last ∼100 years [81]. This pronounced subsidence over the twentieth century has been ascribed to interseismic strain accumulation that has not been reversed by recent earthquakes [81].…”

Fault models of unusual tsunami in the 17th century along the Kuril trench

“…Because the fault plane extends to beneath the land area, the coast is expected to rise at the time of earthquake. Ikeda (1996) proposed that such a giant fault is needed to solve a paradox of crustal strain or movement in the geodetic and geologic time scales (see also Atwater et al, 2004). While the deepest end (85 km) may be below the brittle-ductile transition zone with temperature of about 450…”

Increased precipitation during the Little Ice Age in northern Taiwan inferred from diatoms and geochemistry in a sediment core from a subalpine lake

“…Even extreme events such as floods and earthquakes can be identified using diatoms (Nelson et al 1996;Kashima 2003;Atwater et al 2004;Borromei et al 2010;Schütt et al 2010;Wiklund et al 2010;Saegusa et al 2011). Some environmental variables can be estimated quantitatively using diatom-based transfer functions (Shinneman et al 2009(Shinneman et al , 2010.…”