“Shirasu” is a local name of pumiceous sediments in Kagoshima Prefecture, Japan. It contains non-welded ignimbrite, their secondary deposited sediments (secondary shirasu) and pumice fall deposits and so on. But the usage of the word in such a broad sense has thrown the civil engineering into confusion. So we propose that shirasu must be restricted to non-welded ignimbrite. Typical shirasu in the vicinity of Kagoshima city is the Ito ignimbrite erupted out of the Aira caldera in 22, 000 y.b.p. Shirasu covers the wide area, about 50%, of the Prefecture and forms extensive ignimbrite plateaus. Because of high permeability, surface water is so poor on the plateaus that farmers have to get water from very deep wells of about a hundred meter, or from springs under the marginal cliffs. While it has so high water content that the plateau plays a role of aquifer. Therefore water is supplied constantly to the river even in summer. Landslides, often called “shirasu disasters”, frequently occur at the marginal cliffs in the rainy season. They include surfacial sliding of weathered shirasu and overlying the Satsuma pumice fall deposits (11, 000y. b. p.). City planning on the plateau should include provisions for mitigating potential slope stability and erosion problems. Shirasu is composed of volcanic glass, mineral grains and pumice blocks. The chemical composition shows a high content of SiO2 (70%) and a low one of Al2O3 (14%) and alkali oxides (8%). Various products as follows are manufactured using these physicochemical properties. Pumice is used as light aggregate for concrete. Dressed volcanic glass is applied as grinding powder for optical lenses and Braun tubes and processed into glass microballoon by rapid heating at about 1, 000°C. Zeolites and porous glasses such as vicor glass are also produced.
To identify the detailed nature of the extensional opening system of two active back-arc basins in south Pacific, i.e. the Bismarck Sea and Lau Basin, we deployed the local seismic array of newly developed pop-up type Ocean-Bottom-Seismometers (OBS's). Using P- and S-wave arrival time data, hypocenters of more than two hundred small earthquakes were located with high resolution in both of the two back-arc basins. In the western survey area in the Bismarck Sea, a linear N65°W zone of OBS-located earthquakes defines the major transform fault narrower than 3km. In the eastern survey area, P-wave first motions of the events along stepping WNW-ESE seismic segments suggest the left-lateral strike-slip type focal mechanisms with N20°W T-axes. Therefore, it is inferred that small spreading ridges of en echelon type exist connecting the stepping WNW-ESE seismic segments. In the Lau Basin, an NNW linear trend of OBS-located seismic events has identified, which is continuous to the NW-SE seismic zone along the Peggy Ridge. The seismic trend is composed of several short seismic segments, suggesting a left-stepping en echelon crustal opening system with the NW-SE spreading. Thus we identified the fine-scaled structure of the back-arc spreading systems in the basins. Our result provides useful information of the location of hydro-thermal activity associated with the obliquely extensional spreading.
Since 1960, many industrial estates have been established in the metropolitan areas of Tokyo, Osaka and Nagoya in Japan, which have been of great importance to the rationalization of industrial distribution and regional development. This study is a systematic analysis of how the inland industrial estates have been established under controlling conditions of regulations and laws, location and constructors as well, and how they have evolved with the change of enterprises' strategies, through a case study of the most-developed Northern Kanto Region (Ibaraki, Tochigi and Gunma Prefectures). The results are summarized as follows. (1) The process of spatial diffusion of the inland industrial estates in the Northern Kanto Region can be divided into two periods. Before 1970, the industrial estates were mainly constructed by the Japanese Housing Corporation and the municipal development authorities and largely distributed in those urban developing areas designated by the Law for the Promotion of the National Capital Region. The land transferred to the industrial estates was mostly forested land or dry farmland. Because of the transportation conditions and relevant regulations and laws, the industrial estates in this period were mainly located along the national highways in the zones which were 60-80 or 90-110 kilometers away from the center of Tokyo. After 1971, they were constructed mainly by the prefectural authorities and distributed in those rural areas designated by the Law for the Industrial Promotion in Rural Area, or the northern parts of each prefecture which were designated as depopulating regions. The land transferred was paddy field, marshland or the site of Expo '85. These estates were located near the local roads and the interchanges of the superhighways. (2) There are two different kinds of enterprises, local and invited. The industrial composition is characterized by predominance of machinery and metal working sector, which comprises 51% of the total, represented by the automobiles and auto-accessories industries. As regards the size of enterprises, the small and medium-sized enterprises are predominant, making up 92.6% of the total, showing that the industrial estates have played an important role to accommodate those smaller enterprises. (3) Thirty years have passed since the first industrial estate was established in the Northern Kanto Region. In this period of time, the nature of industrial estates has changed along with the changing development strategies of the enterprises. In the late 1960s, the industrial estates were solely used as the sites of production itself, leaving other functions elsewhere. In the 1970s, besides the productive function, other functions such as distribution facilities, warehouses and affiliated and subcontract plants were altogether introduced into the industrial estates, forming integrated production centers. At the same time, the industrial estates changed from isolated enclaves to integrated part of the local economy. In the 1980s, the enterprises began to direct a new type of activity combining production and research, with the result that the industrial estates with “research” in their names were increased. Thus the industrial estates with higher level of technology and with better living conditions have emerged in the Northern Kanto Region.
The Atotsugawa fault extends 60km or more in the northern Hida Mountains of central Japan, linearly running from ENE to WSW, and forms a master active fault system with predominantly right-lateral component of displacement. A historical large earthquake (1858, M≅7.0) occurred in this region, and many small to micro-earthquakes are taking place along this fault system up the present. A deep trench was excavated across the central part of the Atotsugawa fault where the 5m-high scarplet disturbed the lowest river terrace along the Miya (-gawa) River. The size approximately N-S trending trench was 13m deep in maximum and 22m long across the scarplet (Fig. 1B & 5), and an additional small excavation was made down to clarify the last event at the west side of the main trench, exactly at the southern foot of the scarplet. Several fault planes were exposed on the four trench walls, showing recent movements of the fault which separates the granitic rocks on the hanging-wall side (north) and the younger sediments on the foot wall side. The strike of the main fault is about N70° E and the angle dips 65° N at the surface and 75° N in the trench bottom, increasing the fault angle toward the deeper part. The main results from this survey are summarized as follows : 1) The accumulated vertical offset forming the scarplet is so large at this site that we were not able to correlate the each layers, and sedimentary environment of each side has been quite different due to the displacement, except the basal terrace gravel across the fault. The gravel in the down-thrown side is 2m thicker than that in the up-thrown side. Intrapolating the average vertical slip, at least two events were presumed in the basal gravel. 2) We recognized the “structure D” within the deposits along the main fault disturbed zone, and interpreted that this structure was created by slumping of slope materials from the fault scarplet (see Fig. 13). This phenomenon indicates the sudden movement (earthquake event) of the fault. Dated four events are <820y. B. P., 5200± 200y B. P., 7500±800y. B. P., and 8600±00y. B. P. The latest event (No. 1) was considered to be the 1858 Hietsu Earthquake, as the uppermost humic soils (<820y. B. P.) is thrust up by granitic rocks of the hanging-wall. And, this is also confirmed by existence of a low scarplet at Hayashi (Locality a in Fig. 2), which suggests probably historical fault topography formed within the settlement. 3) Through detailed observation of the trench walls, we found more than 10 events after the formation of the basal gravel which approximate age was estimated to be ca. 12000-13000. However, events of sand deposits at the lower part are not so reliable because it is not easy to detect the key structure in the soft sediments. 4) The average recurrence interval of the main Atotsugawa fault for last 4 events is about 2800years. However, the recurrence interval scatters from 1100 to 5100 years. It is assumed that some events might be missed due to artificial modifications of the fault scarplet and the superficial deposits. In this case, the recurrence interval becomes shorter and the sporadicalness smoother.
Among the Digital Land Information files organized by Geographical Survery Institute, the data of river systems in Japan is supplied in three volumes of relational data files as KS-606, KS-270 and KS-271 (Table 1). The author made a concise and practical data set from those files for the purpose of drawing the river bed profiles. This data set is self-defined, and has the control information as to upstream/downstream linkage, the identifier of individual river system and the value of the pseudo-'stream order' (Table 2). This article reports the process and its logic to generate these attributes, referring the former analysis on the original data set. This generating process was performed by the 'reformer' and the 'linker' shown in Figure 4. The reformer, first, re-constructed the linkage data of the KS-271 file through the selection of the river-mouth of the trunk (Figure 3c). The linker framed the logical river systems by writing the pointers on each record, and masked the channels which should be ignored (Figure 3d). Through the following passes of the linker operation, the individual river systems were identified from each other, and the 'stream orders' were calculated to recognize partial river systems. A sample printout utilizing this data set is shown in Figure 5.