(Front) Map showing S-wave velocity distribution along a curved surface located 10km above the Pacific plate (Nakajima and Hasegawa, 2010). The color scale shows S-wave velocities. The contact zone between the Pacific and Philippine Sea plates is enclosed by two thick broken lines. Red stars denote five M 7-class earthquakes that have occurred in southern Kanto since 1885. Beach balls show the focal mechanisms of the 1921 M 7.0 Ryugasaki earthquake (two solutions shown) and the 1987 M 6.7 east off Chiba earthquake. Black circles represent aftershocks of the 1987 earthquake. (Back) Serpentinized mantle of the Philippine Sea plate at its easternmost portion (shaded in brown). The dashed pink line represents the approximate location of the western boundary of the serpentinized mantle. Grey broken contour lines show depths to the upper surface of the Philippine Sea plate. Green squares and circles plot interplate earthquakes on the upper surface of the Pacific plate, and gray dots plot earthquakes in the mantle of the Philippine Sea plate. Beach balls also show the focal mechanisms of four earthquakes in the mantle of the Philippine Sea plate. The purple circle denotes an aftershock (M 7.1) of the 1923 Kanto earthquake that occurred ∼30h after the main shock. The Philippine Sea plate is being torn into two parts along the dashed pink line: the easternmost portion of the serpentinized mantle subducts at a slower rate, having been left behind the western part, the trunk of the Philippine Sea plate. The pink ellipse denotes a seismic gap pointed out by Okada and Kasahara (1990). (Akira HASEGAWA)
Long-term predictions of geological and tectonic disturbances are key issues for the safety assessment of radioactive waste disposal, especially on the Japanese Islands. Geological predictions of disturbances should be performed by extrapolating uniform mode and rate of crustal movements under the current framework. Multiple lines of geological evidence in Japan strongly suggest that the present mode of tectonics began during the late Pliocene to early Quaternary, and was fully developed by the middle Pleistocene. The uplift rates of mountains in Japan are determined to have been approximately constant until the middle Pleistocene based on simulations of temporal changes in mean altitude developed under concurrent tectonics and denudation processes. The onset of the neotectonic mode of deformation was probably triggered by the initiation of the eastward movement of the Amur Plate and the collision of the Izu block with central Honshu. The uncertainty of predictions beyond steady-state crustal deformation would, in general, increase for long-term predictions using the extrapolation procedure. Consequently, future geological and tectonic disturbances in Japan can be estimated with relatively high reliability for the next 100,000 years.
Recent investigations based on seismic tomography, hypocenter determinations and focal mechanism analyses using dense seismic network data reveal the precise configurations of the Pacific (PAC) and Philippine Sea (PHS) plates subducting beneath the Tokyo metropolitan area. Estimated geometry shows a broad contact zone between the two plates located directly beneath the Kanto plain. The overlap with the PHS plate subducting above it provides the PAC plate with protection from being heated by the hot mantle wedge. Moreover, the fore-arc portion of the PHS plate, before its subduction beneath Kanto, had been cooled by the subduction of the PAC plate from the Izu-Bonin trench. These cause lower-temperature conditions within the two oceanic plates and the upper continental plate beneath the Tokyo metropolitan area. As a result, depth limits of seismic activities within the plates and along their boundaries are anomalously deep. Seismic tomography studies show that the easternmost portion of the PHS slab mantle is serpentinized. The PHS slab may have been torn in two along the western boundary of this serpentinized mantle, with the eastern portion being left behind relative to subduction of the western portion. This is accompanied by the generation of large intraslab earthquakes along the boundary. We need to take these observations into consideration to understand the mechanism generating M7-class earthquakes, which are anticipated to occur in the southern Kanto region with a high probability.
The purpose of this study is to clarify farmers' adaptation strategies to changes in agri-tourism in the Nishino Area, Minami-Alps City, Yamanashi Prefecture. Minami-Alps City is a well-known fruit-growing area in the Kofu basin. The area where cherries are grown is the largest near the Tokyo metropolitan area. For this reason, some farmers started offering a cherry-picking experience and engaged in direct selling to tourists from Tokyo in the 1970s. In the 1980s, agricultural cooperatives started up farm-based tourism businesses. However, in the late 1990s, the drawing power of the farm-based tourism business declined. These changes have made it necessary for farmers to become more entrepreneurial than before as a way of increasing business. Believing that communicating with tourists and consumers is important, farmers adopted management policies in accordance with their needs. Their activities received high evaluations for the diversification of farm management. Entrepreneurial farmers advertised cherry picking and agri-tourism in Minami-Alps City to a broad audience. These activities were effective for individual farms and the area became known as a prosperous agri-tourism spot. On the other hand, farms that have farm labor shortages or use off-farm workers have focused on shipping farm products to agricultural cooperatives rather than engaging in agri-tourism, and reduced the burdens imposed by agri-tourism. This enabled farms engaged in agri-tourism to diversify. Therefore, a large number of farms in this area engage in agri-tourism, which has given a strong image to tourists. The attractions of agri-tourism are enhanced by both the activities of active farmers and stability-oriented farmers.
Although there has been a high interest to investigate the relationship between climate and crop yields in Indonesia, little evidence is available for crops in highland of the country. This study evaluates the relationships between global climate indices (Southern Oscillation Index, SOI; sea surface temperature, SST) and rain-fed crop yields in Gunungkidul district, highland of South-Central Java. Principal Component Analysis (PCA) approach was used to summarize the averaged SSTs during planting season for the El Niño monitoring regions: IOBW (Indian Ocean Basin-Wide), Niño.West and Niño.3. Crops yield of each sub-district of the area was detrended using a 5-year moving average to enhance reliability of the data. For some sub-districts, the first principal component of SSTs was negatively correlated to crop yield residuals of corn and soybean while SOI was positively correlated to that of corn and dryland paddy.
Fluvial and marine terraces have been used as geomorphic indicators to reconstruct the paleoenvironment and estimate crustal movements. This study focuses on the west coast of Ise Bay, where fluvial terraces are widely distributed and active faults have developed. The region is located far from active volcanoes; therefore, terrace chronology and processes of terrace formation during the late Quaternary have been poorly established. This study applies a tephra analysis of aeolian deposits covering terrace surfaces to identify invisible tephra horizons, and discusses the chronology and processes of terrace formation. Furthermore, it estimates crustal movements during the late Quaternary using altitudes of climatic terrace surfaces and data on subsurface geology. The tephra analysis identifies widespread tephras such as Kikai-Akahoya tephra (K-Ah: 7.3 ka) and Aira-Tn tephra (AT: 26–29 ka) from aeolian deposits. Whether or not Kikai-Tozurahara tephra (K-Tz: 95 ka) covered terrace surfaces is assessed from the existence of β-quartz. Based on these tephras and geomorphic features, it is deduced that terrace formation in the study area corresponds to climate changes. In particular, L2 and Md1 terraces that formed during Marine Isotope Stage (MIS) 2 and MIS 5e are important landforms for discussing the processes of terrace formation in response to climate changes. The process of L2 terrace formation indicates that a decrease in precipitation is a major factor of terrace formation upstream during glacial periods. Uplift and subsidence rates during the late Quaternary are estimated not only along active faults but also in areas remote from them. The distribution of uplift and subsidence is consistent with geomorphic and geologic features. This implies that movements of active faults greatly affected geomorphic and geologic development in the study area since they began to move. Based on uplift and subsidence rates across the faults, vertical slip rates of the Yoro, Kuwana, and Yokkaichi faults are estimated at > 1.7 mm/yr, 1.0–1.2 mm/yr, and 0.5 mm/yr, respectively.
The effects of earthquakes in the Kanto district are strongly related to the three-dimensional distribution of the soil mechanical properties of Chuseki-so, which is the name given to incised-valley fills from the Late Pleistocene to the Holocene. To characterize the effects of the sedimentary depositional environment and sedimentary process of Chuseki-so on soil mechanical properties, PS logging test, physical-chemical test, consolidation test, cyclic tri-axial test, and bender element test were conducted on an undisturbed core sample. Based on the test results, we propose a method to estimate the elastic shear modulus of clay soil from conventional soil properties, and discuss the relationship between the sedimentary process of Chuseki-so and the three-dimensional distribution of soil mechanical properties. Through our investigation, we derived the following conclusions: (1) The delta front and inner bay deposits of the Kasukabe core in the Nakagawa Lowland comprise very soft clay and have a high water content and liquidity index; these characteristics are related to the sedimentary depositional environment such as water depth and salinity (ratio of marine diatoms in the sediment). (2) The proposed method can be used to estimate elastic shear moduli on the basis of water content, depth, and locality parameter; in particular, it can be used to evaluate very soft clay, the N value of which is less than 1, on the basis of water content, an easily measurable property. (3) Both bender element and PS logging tests show similar S-wave velocities, and elastic shear moduli measured using the respective tests, G0BE and G0PS, were also similar; therefore, elastic shear moduli can be determined through measurements using these two tests or estimations based on water content. (4) The method to determine the elastic shear modulus, G0TR, which is obtained using a cyclic test, is proposed based on the H-D model; G0TR btained correlates well with G0BE, even if though it is obtained by a different method. The proposed method can be used to determine elastic shear moduli with great accurac.
Sediment cores from Lake Suigetsu, Japan, reveal the absence of seawater intrusion into the lake caused by the historically documented tsunami of AD1586 (Tensho Tsunami). A high-precision chronology of the cores established by Bayesian modeling radiocarbon determinations enables us to ascertain the precise position of the historical event in the sediment depth. Diatom analysis of the core shows that a diatom assemblage dominated by freshwater taxa persisted through the period. This makes a clear contrast with the core section around AD1664 when the lake was artificially connected to the sea by a channel, and the subsequent intrusion of seawater was clearly recorded in the sediment cores by the occurrence of marine diatom fossils.
This paper examines how fruit-producing districts in Iida City and Takamori Town in Nagano Prefecture became largely died-persimmon-producing districts. Apple-, peach-, and Japanese-pear-producing districts were formed in the area in the 1960s and 1970s through the Improvement Project of Agricultural Structure. Most farmers practiced multiple management producing apples, peaches, and Japanese pears. However, since the 1990s, elderly farmers have begun producing dried persimmons as the main crop. The reasons for this are as follows. The production of apples and peaches required much energy, but the elderly farmers were already in their 50s and 60s in the 1990s. In addition, in the 1990s, prices of Japanese pears fell. On the other hand, prices of dried persimmons remained high and stable because of their status as signature agricultural products. Besides, persimmons could be extensively cultivated nearly all year round, with the exception of November and December, when they were processed. Finally, the introduction of fully automatic peeling machines in the 1990s provided the impetus for a substantial increase in dried persimmon production. Quality standards for dried persimmon production have recently been raised since the accession of the regional collective trademark for dried persimmons in 2006. Consequently, it has become difficult for individual elderly farmers to handle all steps of the production process. An issue that needs to be addressed is how dried persimmon production can be increased in the districts.
Most of Edmund Naumann's work on the geology and geography of Japan was translated into Japanese by N. Yamashita (1996). However, a paper titled “Neuere Arbeiten der kaiserlich japanischen geologischen Reichsanstalt (Recent works of the Imperial Geological Survey of Japan),” which appeared in the German Weekly Das Ausland in 1891, had not yet been translated. The paper, which we have now translated, relates to two publications, both published in 1890 by the Imperial Geological Survey of Japan. The first publication is Die japanischen Inseln. Eine topographische-geologische Übersicht (The Japanese Islands. A topographical-geological overview) by T. Harada, who was the deputy director of the survey. Naumann introduced Harada's explanation of the geological systems and geotectonic structures of the Japanese Islands, and, at the same time, severely criticized his concept of the“Fuji Zone,”which was proposed in response to Naumann's“Fossa Magna,”and also the“syntaxis theory,”which interpreted the tectonic relationship between the north and south Japan arcs. The second publication is Beiträge zur Kenntniss der japanischen Landwirthschaft, I, Allgemeiner Teil (Contributions to the knowledge of Japanese agriculture, I. General part) by M. Fesca who was the chief of the agronomical section of the survey. This paper is also an explanatory text of Agricultural Production of the Japanese Empire, Atlas edited by Fesca in 1889. Naumann introduced the contents of the publication in detail, especially that related to climate, vegetation zones, soil characteristics, arable land, and various aspects of agricultural management, and mentioned that he missed the citation of someone's work on agricultural insurance. Naumann's paper is important because it represented not only the results of investigations by the Geological Survey of Japan about ten years after its founding, but also the general situation of geological and agronomical research in Japan around 1890.
Edmund Naumann (1854-1927) wrote “Notiz Ueber die Höhe des Fujinoyama” in 1885 and discussed the history of measuring the height of Mt. Fuji. In particular, he stressed the earliest measurement made in 1828 by Keisaku Ninomiya, a Japanese student of Siebold, who obtained a value of 3,793 m, which is approximately the same as present value. We translated the paper into Japanese because it is important to present scientific knowledge of Mt. Fuji in those days.
Polynesia in the South Pacific is the location of a cluster of hotspots associated with a superswell. A large-scale seismic low-velocity anomaly found in the mantle beneath Polynesia indicates the existence of a superplume, which is responsible for the formation of the hotspot cluster and superswell. Basaltic lavas that erupted at volcanic islands in Polynesia are characterized by a large diversity of radiogenic isotopic ratios. The geochemical characteristics of Polynesian basalts are consistent with the involvement of subducted crustal material in the source mantle, suggesting that Polynesian basalts are products of the large-scale recycling of subducted crustal material facilitated by superplume activity.