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The 2003 Tokachi-oki earthquake ruptured a large area of approximately 100 km2. The location of the largest asperity was estimated to be several dozen kilometres offshore of Hokkaido, Japan. The magnitude measured 8.0 on the Japan Meteorological Agency scale, and several studies used waveform inversion analysis to estimate the moment-magnitude as Mw 8.0–8.2. Several studies reported that there was a minor asperity at the northeastern edge of the fault plane, and that the rupture velocity towards the minor asperity was less than that towards the main asperity. One of them illustrated that the location and timing of the minor asperity were poorly constrained. In this paper, we introduce a procedure based on semblance analysis to image the location of the minor northeastern asperity with improved resolution. We group 15 strong-motion seismographs into three arrays, and we perform semblance analysis on impulsive waves that were possibly generated from the minor asperity and were conspicuously observed at stations in eastern Hokkaido. By projecting the semblance values onto the fault plane, we estimate the location of the minor asperity. We find it to be shallower and farther from the coast than the previous results indicated. The average rupture velocity towards the asperity is estimated to be 2.5 km s−1, which is slower than the 3.6 km s−1 obtained by waveform inversion analysis. [ABSTRACT FROM AUTHOR]

In the Okoppe area of North Hokkaido, Japan, the eruption of adakitic and calc-alkaline dacites was followed by high-Mg andesite (HMA) and calc-alkaline dacite during the Middle Miocene (12–10 Ma). Adakitic dacite is characterized by high Sr/Y and low Y, with Sr and Nd isotopic compositions identical to those of mid-ocean ridge basalt. It has higher MgO contents than adakites generated by experimental melting of metabasalt and amphibolite, and higher Ni and Cr contents than either Archean trondhjemite–tonalite–granodiorite or Early Cretaceous adakitic granites, which are considered to represent partial melts of subducted oceanic crust. This provides compelling evidence that adakitic dacite magma from Okoppe resulted from interaction of a melt derived from subducted oceanic basaltic crust and the overlying mantle wedge peridotite, with little modification to the adakitic melt signature and Sr and Nd isotopic values. The compositional variations in the Toyono adakitic dacite and associated calc-alkaline dacite probably resulted from mixing of the reacted magma and an evolved silicic dacite magma formed by fractional crystallization of the reacted magma. A disequilibrium phenocryst assemblage in the HMA may result from mixing of boninite and silicic andesite that resulted from crustal melting. Calc-alkaline dacites associated with the HMA were derived by fractional crystallization of silicic andesite and assimilation of crust with an enriched Sr isotopic signature. The most likely tectono-magmatic model for the production of adakitic dacite and HMA involves upwelling of hot asthenosphere into the subcontinental lithosphere beneath North Hokkaido and the back-arc side of the NE Japan arc, coincident with the spreading of the Kurile back-arc basin and Japan Sea back-arc basin. This resulted in a high geothermal gradient in the mantle wedge beneath North Hokkaido. The subsequent melting of a limited part of the cool oceanic crust subducting beneath Hokkaido produced adakitic magmas, which interacted with the overlying mantle wedge peridotite. These magmas subsequently reacted with an evolved calc-alkaline melt en route to the surface. Boninitic magma derived from the ascending hot asthenosphere in part reacted with crust-derived silicic andesitic magma, undergoing simultaneous fractional crystallization. [ABSTRACT FROM PUBLISHER]

Radiarta, I N., Saitoh, S-I., and Yasui, H. 2011. Aquaculture site selection for Japanese kelp (Laminaria japonica) in southern Hokkaido, Japan, using satellite remote sensing and GIS-based models. – ICES Journal of Marine Science, 68: 773–780.Japanese kelp (Laminaria japonica) is an important species cultured and harvested in Japan. The most suitable areas for hanging culture in southern Hokkaido were determined using geographic information system (GIS) models and a multicriteria evaluation approach. Analyses of physical parameters (sea surface temperature and suspended solid from SeaWiFS and MODIS) and available bathymetric data indicated that some 74% (1139 km2) of the total potential area with bottom depths <60 m had the two highest suitability scores. A local sensitivity analysis indicated that suspended solids were more important than temperature in affecting model output. This study demonstrates that GIS databases of different formats and sources can be used effectively to construct spatial models for kelp aquaculture. [ABSTRACT FROM PUBLISHER]

The article examines the decline of the coal-mining town of Yūbari in Hokkaido, Japan. Coal was first discovered there in 1888, and by 1953 Yūbari's coal-mining operations employed 19,555 miners. A national policy shift in the late 1950s that de-emphasized coal in favor of oil, though, commenced a decline in Yūbari's fortunes. The author's investigation of this development focuses on three aspects including the city's depopulation amid mine closures, a failed strategy to revive Yūbari's economy via tourism, and decentralization in the early twenty-first century.

Japanese populations of the leaf beetle, Chrysolina aurichalcea, have 2 main karyotypes, Type 31 and Type 41, which greatly differ in chromosome number and form. We examined their geographical distribution and reproductive isolation in southern Hokkaido, northern Japan. Type 41 was widely distributed in the survey area, whereas Type 31 was restricted to a narrow portion. A transect across each karyotypic habitat revealed that both karyotypes co-occurred in a ∼5 km wide zone, with few hybrids or hybrid derivatives. Assessment of the fine scale distribution showed that the 2 karyotypes do not occupy separate microhabitats within the sympatric zone. Karyotype combinations of copulating pairs in the sympatric zone showed no evidence of assortative mating according to karyotype. These findings suggest that postmating isolation between the 2 karyotypes is strong, whereas premating isolation is weak. It does not agree with results from previous studies, which reported a substantial degree of both post- and premating isolation between the karyotypes. Possible causes of the discrepancy in premating isolation are discussed. [ABSTRACT FROM PUBLISHER]

Mustapha, M. A., Sei-Ichi, S., and Lihan, T. 2009. Satellite-measured seasonal variations in primary production in the scallop-farming region of the Okhotsk Sea. – ICES Journal of Marine Science, 66: 1557–1569.Seasonal variation in primary production after a retreat of the sea ice in the scallop-farming region along the Hokkaido coast of the Okhotsk Sea (1998–2004) was determined using satellite images. Annual variability in primary production was caused by variability in the physical processes associated with retreat of the sea ice, advection of the Sōya Warm Current (SWC), and intrusion of the East Sakhalin Current (ESC). Variability in primary production resulted in variability in the Chl a concentration, which was also demonstrated with an empirical orthogonal function (EOF) analysis. Enhancement of Chl a concentration in the frontal area in late spring was demonstrated by the second EOF mode of Chl a concentration (14.2% of variance), in parallel with the generation of a well-developed frontal area resulting from the advection of warm waters of the SWC along the coast in late spring, as indicated by the second EOF mode of sea surface temperature (SST; 1.8% of variance). Elevated Chl a concentration and the presence of cold water of the ESC in late autumn were also highlighted by the third EOF mode of Chl a concentration (9.0% of variance) and SST (1.5% of variance). Prolonged high primary production within the scallop-farming region after spring is supported by the development of a frontal area in summer and strengthening of the ESC in autumn. [ABSTRACT FROM PUBLISHER]

The ascent history of the Horoman peridotite complex, Hokkaido, northern Japan, is revised on the basis of a detailed study of large ortho- and clinopyroxene grains ∼1 cm in size (megacrysts) in the Upper Zone of the complex. The orthopyroxene megacrysts exhibit distinctive M-shaped Al zoning patterns, which were not observed in porphyroclastic grains less than 5 mm in size described in previous studies. Moreover, the Al and Ca contents of the cores of the orthopyroxene megacrysts are lower than those of the porphyroclasts. The Upper Zone is inferred to have resided not only at a higher temperature than previously suggested but also at a higher pressure (∼1070°C, ∼2·3 GPa) than the Lower Zone (∼950°C, ∼1·9 GPa), in the garnet stability field, before the ascent of the two zones. The Horoman complex probably represents a 12 ± 5 km thick section of lithospheric mantle with an ∼10 ± 8°C/km vertical thermal gradient. The current thickness of the Horoman complex is ∼3 km, which is a result of shortening of the lithospheric mantle by ∼0·25 ± 0·1 during its ascent. The Upper Zone appears to have experienced a heating event during its ascent through the spinel stability field, with a peak temperature as high as 1200°C. The effect of heating decreases continuously towards the base of the complex, and the lowermost part of the Lower Zone underwent very minor heating at a pressure higher than ∼0·5 GPa. The uplift and associated deformation, as well as heating, was probably driven by the ascent of a hot asthenospheric upper-mantle diapir into the Horoman lithosphere. [ABSTRACT FROM AUTHOR]

Dunite formation processes in highly depleted peridotites are discussed based upon a detailed study of the Iwanaidake peridotite, Hokkaido, Japan, which consists mainly of harzburgite with a small amount of dunite. In the harzburgites, the Mg# [= 100 × Mg/(Mg + Fe2+)] of olivine ranges from 91·5 to 92·5, and the Cr# [= 100 × Cr/(Cr + Al)] of spinel from 30 to 70; in the dunites, the Mg# of olivine ranges from 92·5 to 94 and the Cr# of spinel from 60 to 85, respectively. The NiO wt % of olivine in harzburgites ranges from 0·38 to 0·44, and in dunites from 0·35 to 0·37. The Mg# and Cr# are higher and NiO wt % is lower in the dunites than in the harzburgites surrounding the dunites. The Mg# and Cr# exhibit normal depletion trends expected from simple partial melting, whereas the NiO wt % shows an abnormal trend. On the basis of mass balance calculations, dunites are considered to be derived from the harzburgites by a process involving incongruent melting of orthopyroxene (orthopyroxene olivine + Si-rich melt). Hydrous conditions were necessary to lower the solidus, and thus melting of harzburgite was probably triggered by the introduction of hydrous silicate melt. The dunite in this massif may have formed in the mantle wedge above a subduction zone. [ABSTRACT FROM PUBLISHER]

The Nikanbetsu peridotite complex, Hokkaido, Japan, is composed of mainly fertile lherzolite, which shows several lines of evidence for incipient partial melting in the spinel–plagioclase facies. There are petrological, textural and mineral chemical variations in plagioclase-free and -bearing lherzolites from the base to the top of the complex within the total thickness of 1400 m. Two-pyroxene and spinel symplectites occur only at the base of the complex. Mass-balance calculations on their bulk compositions suggest that they lost the Al component from pyropic garnet. The Wo content of orthopyroxene cores continuously increases, whereas the Al content decreases from the base upward. Ca–Na zoning patterns of plagioclase in the plagioclase lherzolites characteristically change from W-shaped patterns at the base to oscillatory patterns in the upper part of the complex. These lines of petrological, textural and mineral chemical evidence indicate that incipient partial melting occurred everywhere in the complex, with an increase in the degree of melting from the base toward the top, in proportion to a monotonous rise of the equilibrium temperature from 1100°C to 1250°C. The systematics of plagioclase zoning provides evidence for simultaneous incipient partial melting, melt migration, decompression and melt crystallization in the ascending upper-mantle rocks. [ABSTRACT FROM PUBLISHER]

Spatial distribution relationships between diatom assemblages and water types were investigated in and around a 2-year-old warm core ring in the western North Pacific Polar Frontal Zone off Hokkaido, Japan. From the oceanographic and diatom data, principal component analysis and a clustering technique identified four water types and four diatom assemblages. The Background Assemblage had a low standing stock and was distributed over the entire study area, including the core water of the ring. This assemblage was associated with water conditions that were not highly suitable for diatom growth. A Cold Assemblage, probably linked to submerging Oyashio Water, was found in sub-surface waters. Its standing crop was rather high. The two other assemblages also had relatively high standing stocks: one, the Stratified Assemblage, was found around the nutricline in the sub-surface layer and the other, the Warm Streamer Assemblage, in a warm streamer flowing along the outer edge of the warm core ring. We argue here that the Stratified Assemblage emerged from the Background Assemblage because of favorable local conditions (nutrient level), and, conversely, that in the downstream of the warm streamer, the Warm Streamer Assemblage reversed to the Background Assemblage because the nutrient supply was depleted. [ABSTRACT FROM PUBLISHER]

The canopy structure in terms of the vertical distribution of leaf mass and the degree of asymmetry of competition between individual trees was studied in two types of forest stand in Hokkaido, northern Japan: a naturally regenerated stand of Betula spp. and an artificial plantation of Picea abies.The canopy structure in the Betula stand was more hierarchical; larger individuals were not heavily shaded even in the lowest part of their crowns and smaller individuals were heavily shaded by their larger neighbours. The canopy structure in the Picea stand was less hierarchical; even larger individuals were shaded in the lowest part of their crowns and smaller individuals were not heavily shaded by their neighbours. Application of the general formula of sizedependent mean growth rate revealed that competition in the Betula stand was more one-sided than that in the Picea stand. This result was consistent with the trends in the change over time in size equality in both stands.Even if competition is mediated by light, which often makes competition one-sided, the degree of one-sidedness in competition can be variable depending on canopy structure. [ABSTRACT FROM AUTHOR]

The crustal evolution in the central part of Hokkaido Island, Japan, has been dominated by a series of accretion and collision processes from the late Jurassic to the present. This region is divided into three main tectonic belts (the Sorachi-Yezo, Hidaka and Tokoro belts from west to east) formed in different Cretaceous subduction systems. Since the Miocene, the Sorachi-Yezo Belt and the western part of the Hidaka Belt (the Hidaka Metamorphic Belt, HMB) have suffered severe deformation during two tectonic events: the dextral oblique collision between the North American (Okhotsk) and Eurasian plates and the arc-arc collision of the Kuril forearc sliver with the western part of Hokkaido (the NE Japan Arc). A thrust belt along the western margin of the Sorachi-Yezo Belt is considered to represent the Miocene to Pliocene eastward subduction of the NE Japan Arc due to the compressional stress regime. This subduction jumped to the eastern margin of the Japan Sea in Pleistocene time. The reanalysis of wide-angle seismic data collected in central Hokkaido has provided a new image of crustal-scale structural variation and deformation in the tectonic environments mentioned above. The western part of the Sorachi-Yezo Belt is characterized by a 2-4.5 km thick forearc sedimentary layer with a velocity of 3.0-3.9 km s[sup -1], beneath which a 3.9-5.8 km s[sup -1] body forms an eastward-dipping boundary to the upper unit. This boundary may be the eastward extension of the thrust belt, representing the Miocene to Pliocene plate boundary. A 5.3-5.7 km s[sup -1] body almost crops out beneath the eastern part of the Sorachi-Yezo Belt where ophiolite sequences and highP metamorphic rocks are exposed. Our rather low velocity of 5.3-5.7 km s[sup -1] may suggest that the original oceanic crustal rocks or the metamorphics were fragmented and merged with low-velocity accretionary prism rocks. Plausible tectonic events responsible for this process are fast uplift of a large amount of... [ABSTRACT FROM AUTHOR]

The article presents a case study of a 55-year-old Japanese man woman with cutaneous sporotrichosis in Hokkaido, Japan, characterized by skin lesions chronic erosive nodule. The study involves histopathological assessment of eosin-stained specimens that exhibited a serious epidermal hyperplasia in the dermis of both subjects. It notes that the disease frequently occurs in people living topical and subtropical regions. It suggests the influence of global warming to the prevalence of the disease.