U–Pb zircon age from the radiolarian‐bearing Hitoegane Formation in the Hida Gaien Belt,Japan

The dating of radiolarian biostratigraphic zones from the Silurian to Devonian is only partially understood. Dating the zircons in radiolarian‐bearing tuffaceous rocks has enabled us to ascribe practical ages to the radiolarian zones. To extend knowledge in this area, radiometric dating of magmatic zircons within the radiolarian‐bearing Hitoegane Formation, Japan, was undertaken. The Hitoegane Formation is mainly composed of alternating beds of tuffaceous sandstones, tuffaceous mudstones and felsic tuff. The felsic tuff and tuffaceous mudstone yield well‐preserved radiolarian fossils. Zircon grains showing a U–Pb laser ablation–inductively coupled plasma–mass spectrometry age of 426.6 ± 3.7 Ma were collected from four horizons of the Hitoegane Formation, which is the boundary between the Pseudospongoprunum tauversi to Futobari solidus–Zadrappolus tenuis radiolarian assemblage zones. This fact strongly suggests that the boundary of these assemblage zones is around the Ludlowian to Pridolian. The last occurrence of F. solidus is considered to be Pragian based on the reinterpretation of a U–Pb sensitive high mass‐resolution ion microprobe (SHRIMP) zircon age of 408.9 ± 7.6 Ma for a felsic tuff of the Kurosegawa belt, Southwest Japan. Thus the F. solidus–Z. tenuis assemblage can be assigned to the Ludlowian or Pridolian to Pragian. The present data also contribute to establishing overall stratigraphy of the Paleozoic rocks of the Fukuji–Hitoegane area. According to the Ordovician to Carboniferous stratigraphy in this area, Ordovician to Silurian volcanism was gradually reduced to change the sedimentary environment into a tropical lagoon in the early Devonian. And the quiet Carboniferous environment was subsequently interrupted, throwing it once more into the volcanic conditions in the Middle Permian.     

Surface currents around Hokkaido in the late fall of 1981 obtained from analysis of satellite images

This paper describes the characteristics of currents around Hokkaido using a current vector map compiled by chasing the displacement of sea marks on a pair of successive thermal infrared images taken from a satellite, NOAA-6. The points of some sea surface patterns showing distinctive features which can be commonly identified in both images are called Sea Marks≓. This sea mark chase method≓ has a great advantage over velocity measurements by boats or buoys, in that it gives a synoptic view of the velocity distribution over a broad sea area extending for some hundreds of miles on a short time scale of half a day.In order to investigate the current in the late fall of 1981, we used the data taken at 19:05 JST on 30 October and at 7:20 JST on 31 October. With these data taken with a 12 hr difference, the measurement accuracy of the speed of sea marks reached ±0.1 knot through geometrical correction. The velocity vectors of sea marks agreed with results of GEK measurements performed on those days, and also with the mean current pattern obtained in the past based on sea surface data.The most distinct features recognized were some cyclonic and anticyclonic eddies of the order of 100 km in diameter which dominated in the Kuril Basin of the Okhotsk Sea. They appeared clearly in the original NOAA images and their physical parameters were determined quantitatively from the vector map. These eddies were located in the region of decay of the Soya Warm Current and were rotating at a speed nearly as large as that of the current. The problems of what feeds energy to these eddies and how long they live remain to be solved in future studies.     

Detrital zircon geochronology of the Cretaceous Sindong Group,Southeast Korea: Implications for depositional age and Early Cretaceous igneous activity

The Sindong Group forms the lowermost basin‐fill of the Gyeongsang Basin, the largest Cretaceous nonmarine basin located in southeastern Korea, and comprises the Nakdong, Hasandong, and Jinju Formations with decreasing age. The depositional age of the Sindong Group has not yet been determined well and the reported age ranges from the Valanginian to Albian. Detrital zircons from the Sindong Group have been subjected to U–Pb dating using laser ablation inductively coupled plasma mass spectrometry. The Sindong Group contains noticeable amounts of detrital magmatic zircons of Cretaceous age (138–106 Ma), indicative of continuous magmatic activity prior to and during deposition of the Sindong Group. The youngest detrital zircon age of three formations becomes progressively younger stratigraphically: 118 Ma for the Nakdong Formation, 109 Ma for the Hasandong Formation, and 106 Ma for the Jinju Formation. Accordingly, the depositional age of the Sindong Group ranges from the late Aptian to late Albian, which is much younger than previously thought. Lower Cretaceous magmatic activity, which supplied detrital zircons to the Sindong Group, changed its location spatially through time; it occurred in the middle and northern source areas during the early stage, and then switched to the middle to southern source areas during the middle to late stages. This study reports first the Lower Cretaceous magmatic activity from the East Asian continental margin, which results in a narrower magmatic gap (ca 20 m.y.) than previously known.     

Distribution of phototrophic bacteria in Omura Bay during the summer with special reference to brownChlorobium

The distribution of phototrophic bacteria was investigated during the summers of 1969 and 1970 in Omura Bay of western Kyushu. Phototrophic sulfur- and nonsulfur-bacteria were distributed numerously in the mud and bottom water. Brown strains usually dominated in number. In water column, other than bottom water, there were usually few or no phototrophic bacteria. On occasion, however, a large number of brown bacteria were found in the middle of water column. Six strains, two each of the purple, green and brown bacterial colonies, were isolated from mud and sea water. The purple and green bacterial strains were identified as belonging to the generaChromatium andChlorobium, respectively. The brown strains could not be identified using Bergey's manual, but were found to be similar to the brownChlorobium described byPfennig. All six strains required sulfide for growth. Heterotrophic tendency was greater for the purple and green strains than for the brown strains. Their growth was enhanced by the addition of thymine. Living cells, taken from enrichment cultures of mud samples from four stations, gave absorption spectra almost identical to the spectrum of brownChlorobium. Thus it appears that during the summer brownChlorobium is the dominant phototrophic bacterial group in Omura Bay.     

近期东北主要城市遥感监测与动态分析

在GIS支持下,以LandsatTM、ETM和SPOT数据为主要信息源,采用栅格数据与矢量数据相结合、多源与多时相数据相结合、多种信息相结合、内业处理与外业调查相结合的技术路线,建立东北三省主要城市环境分析信息系统,对10多年来城市演变规律、趋势进行了遥感动态监测分析,为环境管理与决策服务。     

Thermoelastic properties of chromium oxide Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> (eskolaite) at high pressures and temperatures

A new synchrotron X-ray diffraction study of chromium oxide Cr₂O₃ (eskolaite) with the corundum-type structure has been carried out in a Kawai-type multi-anvil apparatus to pressure of 15 GPa and temperatures of 1873 K. Fitting the Birch–Murnaghan equation of state (EoS) with the present data up to 15 GPa yielded: bulk modulus (K _0,T0), 206 ± 4 GPa; its pressure derivative K′_0,T , 4.4 ± 0.8; (?K _0,T /?T) = ?0.037 ± 0.006 GPa K^?1; a = 2.98 ± 0.14 × 10^?5 K^?1 and b = 0.47 ± 0.28 × 10^?8 K^?2, where α _0,T  = a + bT is the volumetric thermal expansion coefficient. The thermal expansion of Cr₂O₃ was additionally measured at the high-temperature powder diffraction experiment at ambient pressure and α _0,T0 was determined to be 2.95 × 10^?5 K^?1. The results indicate that coefficient of the thermal expansion calculated from the EoS appeared to be high-precision because it is consistent with the data obtained at 1 atm. However, our results contradict α ₀ value suggested by Rigby et al. (Brit Ceram Trans J 45:137–148, 1946) widely used in many physical and geological databases. Fitting the Mie–Grüneisen–Debye EoS with the present ambient and high-pressure data yielded the following parameters: K _0,T0 = 205 ± 3 GPa, K′_0,T  = 4.0, Grüneisen parameter (γ ₀) = 1.42 ± 0.80, q = 1.82 ± 0.56. The thermoelastic parameters indicate that Cr₂O₃ undergoes near isotropic compression at room and high temperatures up to 15 GPa. Cr₂O₃ is shown to be stable in this pressure range and adopts the corundum-type structure. Using obtained thermoelastic parameters, we calculated the reaction boundary of knorringite formation from enstatite and eskolaite. The Clapeyron slope (with \({\text{d}}P/{\text{d}}T = - 0.014\) GPa/K) was found to be consistent with experimental data.     

Detailed paleoseismic history of the Hinagu fault zone revealed by the high-density radiocarbon dating and trenching survey across a surface rupture of the 2016 Kumamoto earthquake,Kyushu, Japan

The NE-trending Hinagu fault zone, length 81 km, is one of the major active faults in Kyushu, Japan. From north to south, it is divided into three segments based on geomorphic features and paleoseismic behavior: the Takano-Shirahata, Hinagu, and Yatsushiro Sea segments. The 2016 Kumamoto earthquake produced a 6-km-long surface rupture with a dextral strike-slip displacement on the northern part of the Takano-Shirahata segment. Surface rupture, a faint east-side-up flexure with a vertical offset of less than 8 cm, was observed near the middle of the Takano-Shirahata segment. To examine past surface-rupturing earthquakes on the Takano-Shirahata segment, including rupture frequency and timing, we conducted a paleoseismic study with boring and trenching at Yamaide. A trench across the surface rupture exposed multiple fault strands associated with multiple surface-rupturing events that deformed several strata of fine-grained sediments. By structural and stratigraphic interpretation, high-density radiocarbon dating and tephra analysis, and Bayesian modeling, we constrained the timing of seven events, Events 1–7, to 0.84–1.25, 1.31–7.06, 9.99–11.0, 10.8–12.1, 12.0–13.0, 14.2–15.1, and before 14.8 kcal BP. Slip during Events 1–6 was obviously larger than the 2016 slip. The estimated average recurrence interval was about 2596–2860 years, but the interval between Events 2 and 3 was much longer than other intervals. Moreover, the vertical throw associated with Event 2 was larger than that of other events. This implies that the Takano-Shirahata segment has a period with rare larger earthquakes and a period with frequent smaller earthquakes. Some events might have produced ruptures on both the Takano-Shirahata and the northern part of the Hinagu segments simultaneously or in a short time. The variety of recurrence intervals suggests that the seismic activity has been affected by one or both activities of the Futagawa fault zone and the Hinagu segment.     

城市土地利用变化中邻域相互作用的特征——日本三大都市圈的比较研究

Local spatial interaction between neighborhood land-use categories (i.e. neighborhood interaction) is an important factor which affects urban land-use change patterns. Therefore,it is a key component in cellular automata (CA)-based urban geosimulation models towards the simulation and forecast of urban land-use changes. Purpose of this paper is to interpret the similarities and differences of the characteristics of neighborhood interaction in urban land-use changes of different metropolitan areas in Japan for providing empirical materials to understand the mechanism of urban land-use changes and construct urban geosimulation models. Characteristics of neighborhood interaction in urban land-use changes of three metropolitan areas in Japan,i.e. Tokyo,Osaka,and Nagoya,were compared using such aids as the neighborhood interaction model and similarity measure function. As a result,urban land-use in the three metropolitan areas was found to have had similar structure and patterns during the study period. Characteristics of neighborhood interaction in urban land-use changes are quite different from land-use categories,meaning that the mechanism of urban land-use changes comparatively differs among land-use categories. Characteristics of neighborhood interaction reveal the effect of spatial autocorrelation in the spatial process of urban land-use changes in the three metropolitan areas,which correspond with the characteristics of agglomeration of urban land-use allocation in Japan. Neighborhood interaction amidst urban land-use changes between the three metropolitan areas generally showed similar characteristics. The regressed neighborhood interaction coefficients in the models may represent the general characteristics of neighborhood effect on urban land-use changes in the cities of Japan. The results provide very significant materials for exploring the mechanism of urban land-use changes and the construction of universal urban geosimulation models which may be applied to any city in Japan.     

Nine unusually large tsunami deposits from the past 4000 years at Kiritappu marsh along the southern Kuril Trench

Large earthquakes along the Kuril subduction zone in northern Japan are known to have caused damaging tsunami, although there is a little information on historical earthquakes and tsunami in this area because no documents exist before the 19th century that might refer to tsunami events. To determine the likely timing and size of future events we need information on their recurrence intervals and to do this for the prehistoric past we have investigated sediments located in the Kiritappu marsh in eastern Hokaido that we interpret as laid down by tsunami. Using reliable multiple lines of evidence from sedimentological, geomorphological, micropaleontological, and chronological results, we identify 13 tsunami sands. Two of these lie within a peat bed above a historical tephra, Ta-a (AD 1739); the upper one probably corresponds to the AD 1843 Tempo Tokachi-oki earthquake (M 8.2) tsunami, and the lower to either the AD 1952 Tokachi-oki earthquake (M 8.2) tsunami or the AD 1960 Chilean earthquake (M 9.5) tsunami. Underlying are 11 prehistoric tsunami sand beds (nine large sand beds and two smaller sand beds) deposited during the past 4000 years. Because of the wide spatial distribution of the large sand beds, and inundation distances inland of between 1200 to 3000 m, we suggest that they record unusually large tsunamis along the Kuril subduction zone. According to our analyses, these tsunami sands were derived from the coastal area and, although they do not show clear graded bedding, they commonly have gradational upper boundaries and erosional bases and include internal sedimentary structures such as plane beds, dunes, and current ripples, reflecting bedload transportation. Based on our results we calculate the recurrence interval of unusually large earthquakes (probably M 8.6) along the Kuril subduction zone as about 365–553 years and estimate the youngest large event to have occurred in the 17th century.     

Life‐cycle cost analysis based on a renewal model of earthquake occurrences

A decision methodology for the management of seismic risk of a single building is presented. The decision criterion aims at minimizing the expected life‐cycle cost, including the initial cost of the design and the expected cost of damage due to future earthquakes. The expected life‐cycle cost of each design alternative is formulated using a renewal model for the occurrence of earthquakes in a seismic source, which accounts for the temporal dependence between the occurrence of ‘characteristic’ earthquakes. The formulation involves the expected damage cost from an earthquake of specified magnitude in a given source. This term is estimated by simulating the processes of fault rupture, elastic wave propagation, surface soil amplification, dynamic structural response and generation of damage costs. As an example, the methodology is applied to an actual office building in Tokyo. A simple decision problem between two design alternatives is set: a bare steel moment frame, and the same frame equipped with oil dampers. Through this case study, the installation of the oil dampers is demonstrated to be effective in reducing the life‐cycle cost of the building under consideration. Copyright © 2004 John Wiley & Sons, Ltd.