Osaka Plain Research Articles

On the Relationship between Azimuth Dependency of Earthquake Ground Motion and Deep Basin Structure beneath the Osaka Plain.

The typical characteristics of earthquake ground motion in the Osaka Plain are the later arrivals with large amplitudes that are considered to be generated at the edges of the basin structure. We found that the amplitudes of later arrivals have the azimuth dependency according to the location of the epicenters; the amplitudes of the later arrivals generated by the southern earthquakes are larger than those generated by the northern earthquakes. It is, found that the azimuth dependency is not caused by the source effects but by the effects of the basement structure. The basin structure of the Osaka Plain in the N-S direction was obtained through refraction seismic surveys. The survey lines were extended in both north and south directions from the explosion point at a northern area of the Osaka Port; each line had a length of 20-30 km.The modified Aki and Lamer (A-L) method was applied to study the azimuth dependency of the amplitudes of the later arrivals using the surveyed N-S section. From the calculation, the later arrival had a group velocity of 600 m/s which corresponded well to the observed velocities. The azimuth dependency, however, was not well simulated. It is supposed that the incongruity was caused by insufficient information on the edge structure of the sedimentary basin and the structure of shallow sediments.

深層ボーリングデータによる大阪平野北部の中・古生界

深層ボーリングデータによる大阪平野北部の中・古生界

大阪平野の地下構造

大阪平野の地下構造

遺跡から得られた過去の地震情報

Numerous evidences of paleoearthquakes have been discovered in many archaeological sites. The present writer has investigated on these evidences and comes to the following conclusions;1) Some traces of the Paleo-Nankai and Tokai earthquakes were found mainly along the Southwestern Pacific coast. The present writer infers from these archaeological evidences and old documents that these great earthquakes occurred simultaneously in the years A. D. 1498 and A. D. 684.2) The ages of the faultings which caused big earthquakes, were revealed in some regions. For instance, the fault movement along the northern rim of the Osaka Plain is proved to have occurred in the years A. D. 1596 and about A. D. 500.3) Traces of sand eruption were found out in many sites. Some important behaviors of sand layers, caused by a liquefaction, were observed in these traces.

First Record of Egg-laying of the Common Cuckoo Cuculus canorus in the Osaka Plain

First Record of Egg-laying of the Common Cuckoo Cuculus canorus in the Osaka Plain

たい積物中の火山ガラスの研究 大阪平野の更新〜完新統について

The Pleistocene to Holocene sediments underlying the Osaka Plain consist of unconsolidated gravels, sands, silt and clay beds of limnic, fluvial and marine origin.IKEBE et al. (1970) and FURUTANI (1978) described the subsurface geology of the Osaka Plain is through the investigation of the drilling cores. From these studies the subsurface stratigraphy of the Osaka Plain summarized as the following sequence, the latest Pleistocene to Holocene formation (Nanba Formation), the upper Pleistocene formation (Ma 11 bed, Ma 12 bed and Tenma Formation) and the Osaka Group in descending order (Figs. 1 and 2).The writer investigated the content of glass fragments in these sediments and also studied the features such as shape and refractive index of glass fragments.The results obtained are the following:1) The content and the features of glass fragments from the Pleistocene to Holocene sediments are shown in Fig. 3, 4, 5, 6, 7, 8, 9, and 10.2) On the basis of the vertical variation-diagram (Figs. 3…10), volcanic ash- horizons can be found in these sediments, because the vertical variations of content and features of glass fragments are controlled mainly by the fall of volcanic ash.3) Five volcanic ash-horizons occur in these sediments and are widely traceable. Among these five horizons, three horizons are in the Ma 12 bed, and two horizons are in the Nanba Formation.4) The lower ash-horizon in the Nanba Formation can be correlated with the ash layer described by MAEDA (1976) in Core Site 2. The upper ash-horizon in the Nanba Formation can be correlated with the ash layer described by ISHIDA et al. (1969) in the Kyoto Basin.

大阪周辺地域におけるウルム氷期以降の森林植生変遷

Pollen diagrams are represented from core samples taken from five boreholes in the Tenma Formation (lower terrace deposits) and the Nanba Formation (Alluvial deposits) in the Osaka plain. On the basis of pollen stratigraphy the diagrams are divided into two local pollen assemblage zones (E and F) including 11 sub-zones (E 1-5 and F 1-6). The forests characteristically inferred from the pollen assemblage are Castanopsis-Quercus (Cyclobalanopsis) Forest, Abies firma-Tsuga sieboldii Forest, Fagus Forest and Subalpine coniferous Forest. A considerable number of pollen grains preserved are thought to be derived from catchment areas of each river as the deposits accumulated.The forest history of the area is as follows.E1-E3 sub-zone; Subalpine coniferous Forest and Fagus Forest were extensive to cover the area from about 30, 000y.B.P. to 20, 000y.B.P..E4 sub-zone; Subalpine coniferous Forest was the most widely spread over to the area between 20, 000y.B.P. and 18, 000y.B.P. (?).F1-F2 sub-zone; Fagus Forest was widely expanded to the lowland area in the early Holocene (10, 000y.B.P.-7, 500y.B.P.).F4 sub-zone; Castanopsis-Quercus (Cyclobalanopsis) Forest was widely developed in the lowland area in the middle Holocene (6, 000y.B.P.-2, 500y.B.P.)F6 sub-zone; These forests were replaced by a secondary forest in the latest Holocene (since 1, 500y.B.P.).

FAULT TOPOGRAPHY AND QUATERNARY FAULTING ALONG THE MIDDLE AND EASTERN PARTS OF THE ARIMA-TAKATSUKI TECTONIC LINE, KINKI DISTRICT, CENTRAL JAPAN

The Arima-Takatsuki Tectonic Line (ATL), located on the northwestern rim of the Kinki Triangle, is an active fault zone developed along the geologic boundary separating the Tanba Zone of Paleozoic rocks to the north and the Ryoke Zone of granite to the south. Along the middle and eastern parts of this tectonic line, limiting the northern border of the Osaka Plain, displacements of terrain features, mainly terrace surfaces (dissected fans), due to fault activities can be clearly observed. The writer has investigated these displaced topographies and attempted to elucidate the nature of fault activities of the middle and eastern parts of the ATL. The findings can be summarized as follows. 1) Faults in this area, trending either E-W or ENE-WSW, can be classified into three types, those having: 1) displaced terrace surfaces vertically, and valleys cutting these surfaces dextrally, such as Kiyoshikojin and Satsukioka Faults; 2) formed shallow depression zones such as Hanayashiki, Koyaike and Ibaraki Depressions in the E-W direction on the terrace surfaces; and 3) cut through and displaced valleys in the mountains on the north, such as Ishizumitaki, Satsukioka, Minoo and Nyoidani Faults. 2) Rates of displacements have been computed by estimating ages of the terrace sur-faces and valleys dissecting these surfaces; for type 1), 0.5-1.5m/103 years dextrally and 0.06-0.2m/103 years vertically, and for type 2), a maximum of 0.8m/103 years in vertical direction. 3) The active fault system of the Rokko Mountains is continuous to that of the study area. Active faults of both regions are distributed in the shape of E-W extending wedge, with the tip pointing to the eastern end of the study area. These fault systems have been active in the second half of the Quaternary under the stress field of E-W compression. Accordingly, NE-SW trending faults have greater amounts of vertical displacements than ENE-WSW trending faults, with both having dextral movements. 4) The Median Tectonic Line (MTL), bordering the base of the Kinki Triangle, is also an E-W trending geologic boundary. Along active faults associated with the MTL, the rates of displacements both in vertical and dextral directions are twice as great as those found for the active faults of the ATL. Distribution of type 3) faults of the ATL is similar to that of the MTL in the sense that both are located on the northern side of geologic boundaries.

GEOMORPHIC DEVELOPMENT AND CRUSTAL MOVEMENT OF THE MIDDLE COURSE BASIN OF THE KINOKAWA RIVER

The Median Tectonic Line (MTL) extends more than 800km long in the middle part of Southwest Japan, dividing it into the Inner and Outer Zones. The middle course basin of the Kinokawa River dealed here has been formed on the south side of the MTL in the middle part of the Kii Peninsula. The thick Plio-Pleistocene to middle Pleistocene sediments cover the basin and various forms of river terraces are observed. The writer has investigated the geomorphic development of the area, closely relating to the Quaternary crustal movements of Inner and Outer Zones. The results are as follows. The Plio-Pleistocene to middle Pleistocene sediments are divided into the lower (Shobudani Formation) and the upper (Gojo Formation). The Shobudani Formation consists, in most cases, pebbles, cobbles, gravels, sands, silts and clays, which are considered to be deposited in lacustrine environment. On the other hand, the Gojo Formation consists of wellrounded boulders, transported by the Paleo-Kinokawa River, and rarely of silts and clays, unconformably overlying the Shobudani Formation and the bed rock. Thrust faults along the MTL are sometimes recognized which cut the Shobudani Formation and are overlaid by the Gojo Formation. The river terrace surfaces can be classified into seven, i.e., Gojo, Yamada, Koino, Yamakage, Nohara, Futami and Imai surfaces in descending order. The Yamada surface is correlated to the Higher terrace surface in the south Osaka Plain. The highest terrace (Gojo surface) may be the depositional surface of the Gojo Formation from the geomorphological and geological point of view. The age of the deposition of the Gojo Formation, i.e., the final formation of the Gojo surface is thought to be during the middle Pleistocene. This age is very important in many aspects as follows; 1) During the early Pleistocene, there existed a E-W trending narrow lake along the MTL. In the middle Pleistocene, however, the Gojo Formation was accumulated as the river deposits of the Paleo-Kinokawa River, forming its depositional surface as the Gojo surface. Since then, the Kinokawa River cut the above terrace surface by deepening. 2) Simultaneously with the deposition of the Gojo Formation, Kii Mountains south of the MTL started severe uplift, supplying coarse gravels into the Kinokawa River Basin. On the other hand, Izumi Mountains of the north also began to rise up, accompanied by the upheaval of Kongo Mountains. 3) The older fault system showing thrust movements along the MTL has become inactive, and the younger fault system parallel to it has become active predominantly showing the dextral strike-slip movements since the age of the deposition of the Gojo Formation.

生駒山頂における蚊の採集成績, 特にコガタアカイエカ Culex tritaeniorhynchus summorosus の生理的年令について

From 1968 to 1971,mosquitoes were collected on the top of Mt. Ikoma, 642m above sea level by using a dry ice light trap, for one hour after sunset once a week during the period from June to September. The unfed females of Culex tritaeniorhynchus summorosus collected in 1970 were dissected to determine the physiological age composition and to observe the developmental stage of follicles. For comparison, similar surveys were conducted in paddy fields at three sites on the Osaka plain. 1) On the top of Mt. Ikoma, 9 species of mosquitoes were found. C. tritaeniorhynchus summorosus was the dominant species throughout the four years, followed by Anopheles sinensis and Aedes vexans nipponii. 2) Although the pattern of seasonal prevalence of C. tritaeniorhynchus summorosus females at the top of Mt. Ikoma is similar to that on the Osaka plain, the number in the former site generally tends to increase later and decrease earlier than in the latter site. 3) Even at the top of Mt. Ikoma, many parous females of C. tritaeniorhynchus summorosus were found. They were, for the most part, uniparous, with a few biparous. The greater the number of mosquitoes collected, the lower the parous rates. 4) The percentages of females with follicles at IIb or more advanced stages were generally higher both in nulliparous and uniparous females on Mt. Ikoma being apart from paddy fields than on the Osaka plain.

THE MAKING OF THE “SHIMA-HATA” LANDSCAPE IN THE “JORI-SYSTEM”

In the Osaka Plain, the Nara Basin, the Kyoto Basin, the Ise Plain and the Nobi Plain, cultivated hatake (fields other than rice-fields) called “Shima-Hata” are often found in the rice-fields which are based on the ancient “Jon-System”. The “Shima-Hata” is an island-like or micro-mesa like upland field in each piece of the rice-fields. This paper is to make a historico-geographical research on the process of the changing rural landscape in Japan. The present writer investigated when the “Shima-Hata” land-scape was made and what were the conditions necessary for its appearance. As a result of the investigation, the following conclusions have been found. (1) The first historical document in which the above-mentioned “Shima-Hata” can be clearly recognized appeared at the end of the 14th century. Before the 12th century, however, it is thought that the “Shima-Hata” landscape did not exist. In consequence it is presumed that the “Shima-Hata” landscape was made in the 13th century or the 14th century for the first time. (2) In the ancient “Ritsuryo” period, cultivated hatake other than rice-fields could be owned privately, while the rice-fields were possessed by the State. Hatake were under-valuated in comparison with the rice-fields. In the Medieval Ages, however, difference in official evaluation between hatake and the rice-fields dissolved, and a higher value was attached to hatake according to the advance of intensive utilization. It is in these Medieval Ages that the socially and economically basic conditions for the making of the “Shima-Hata” landscape were fulfilled. Therefore, it is to be said that the “Shima-Hata” land-scape was closely connected with the intensive cultivation in and after the Medieval Ages. This conclusion is consistent with the above-stated (1). (3) The process of making the “Shima-Hata” landscape that the present writer has mentioned in (1) and (2) is also proved by the survey of microgeomorphology and surface geology. (4) There are two ways of making the “Shima-Hata”. A. By digging rice-fields located at the middle of a natural levee in order to obtain well-irrigated rice-fields. B. By piling up mud at one part of each rice-field on a flood plain.

A Study On Propagation Characteristics Of Surface Wave On Sedimentary Layers Based On Earthquake Observations

Seismological observation on Osaka Plain has revealed the existence of ATOYURE» > . » > . * > . • > , or surface wave in the sedimentary layer with a period of 1.0 to 1.5 seconds, which follows the principal motion. ATOYURE is characteristic of earthquake motion observed on the sedimentary layer of the plain. The results of our study, based on the analysis of observed waveforms and the determination of theoretical dispersion curves, show that or surface wave in the sedimentary layer, indicates the characteristics of both Love and Rayleigh waves in the wide frequency range from 0. 3 to 1. 5Hz. Evidently surface wave, with a characteristic dispersion, propagates from the boundary region between the plain and surrounding mountains throughout the plain. INTRODUCTION Ever since the great Mexican earthquake of 1985, surface wave (motion with a relatively long period) propagation through the sedimentary layer of a plain has been regarded as a key factor in discussing earthquake motion in a plain. Prior to the earthquake in Mexico, surface wave propagation through the sedimentary layer of a plain had been observed in the Osaka Plain and reported as ATOYURE. Importance had not been attached to this motion which, though limited in scale, had not caused significant damage. However, this motion is an important factor in ensuring the safety of a large and long-span structure in the event of earthquake: the acceleration amplitude of ATOYURE sometimes exceeds that of principal motion, though ATOYURE, occurring after the principal motion, is a simple motion without a harmonic. This report based on earthquake observation records and the results of theoretical analysis, to discusses the characteristics of surface wave propagation through the sedimentary layer of the Osaka Plain. Transactions on the Built Environment vol 3, © 1993 WIT Press, www.witpress.com, ISSN 1743-3509

Latest Quaternary Deposits of the North-western Part of Osaka Plain

The research on the process of the development of the alluvium forming coastal plain can be effectively combined with the studies of the adjoining submarine sediments. Fortunately the opportunity to make such an effective work has been offered by the sonic method survey of Osaka Bay in 1962. In this paper, part 1, the writers intend to describe and discuss about the latest Quaternary deposits of Amagasaki area, the western part of Osaka coastal plain north of Osaka Bay.Fig. 2 is the panel diagram showing the final result of compilation of many subsurface data from boring cores. A prominent gravel bed which is named Itami gravel spreads over the whole area. The younger marine and fluvial deposits covering the Itami gravel are treated in this paper. They are so-called “alluvial deposits” and are divided into two parts, the Upper and the Lower, based on the cycle of sedimentation.The base of the “alluvial deposits” is mapped in Fig. 5. The Itami gravel had been entrenched by older rivers which almost coincide in distribution with the present river system and the older channels were buried by the deposition of the “alluvium”. The older river system can be traced to buried channels detected on the surface of the basement of the “alluvial deposits” in Osaka Bay.A line of the buried wave-cut cliff or slope can be recognized somewhat to the north of the present shore line, about 20m below the present sea-level. The cliff is inferred to show the shore line when the Lower part of the “alluvial deposits” was formed.The writers have established the following processes of sedimentation of the “alluvial deposits” of the area.1) Large-scale regression and the deep entrenchment of rivers on the surface of the Itami gravel, Considering the extension of the river channels to the basement of the “alluvial deposits” in Osaka Bay, this inner bay must have been dried up completely at that time. This stage may be identified with the maximum phase of the Wurm Ice Age.2) Starting of transgression, The Lower part of the “alluvial deposits” was formed burying the river floors of the older river system.3) Retardation of transgression. The sea-level retarded at about 20m below the present sea-level. This stage is inferred to be identified with the Allerod oscillation, according to a chronological datum of 14C obtained from the lowest horizon of the Upper part or the top of the Lower part of the “alluvial deposits” in Osaka.4) Rapid re-transgression. The Upper part of the “alluvial deposits” was formed. Wavecut cliffs at the highest sea-level have been preserved about 5m above the present sea-level.The processes stated above almost coincide with those traced in and around Tokyo Bay (HATORI & others, 1962). This fact indicates that the formation of the “alluvial deposits” is closely related to the ecstatic changes of sea-level.

THE GEOMORPHOLOGICAL DEVELOPMENT OF THE NORTH-WESTERN OSAKA PLAIN

The Osaka Basin which is located in the east end of the Inland Sea of Japan, is filled with the Plio-Pleistocene deposits, so called the Osaka Group, of clay, sands and gravels. It graddually becomes of marine origin with alternation of marine and nonmarine stratum. The Plio-Pleistocene is exposed in the platforms and the hills in and around the Osaka Plain of which the height ranges from several tens meters to about 200 meters. On the sides of the surrounding mountains, we observe the disturbed Osaka Group, influenced by the uplifting movement of the mounatins. Generally speaking, it is complicatedly disturbed by f lexture, fold and overthrust, but it is safely concluded that the Plio-Pleistocene is dislocated to rise generally from the deltaic plain to the margins of the basin, and, so to say, that the Plio-Pleistocene deposits slightly decline to disappear into the bottom of the bay, or below the deltaic deposits. In another view, the the distribution of the deltaic deposits can be said to be restricted to the depressed area, provided by the basin building movement. The hills in the uplifted area present tectonic morphology. The late Pleistocene platforms of which the inclination be comes steeper with their being older (higher), cut the Osaka qroup which dips in the same direction. Both the surfaces or the prolonged surfaces of the platforms cross together and sink into the deltaic deposits in the depressed area. On the other hand, the Pleistocene below the deltaic deposits, it is suggested by boring, have sedimentary cycle of clay and gravels or coarse materials. It can be said hypothetically that the sedimentary cycle is possibly of eustatic origin. To say conclusively, the geomorphology of the hills is under the control of tectonic movements, but eustatic control is over the sedimentation below the delta. The several hundreds of boing data in which the locations of the main ones are shown in Fig. 1, show us that each layer is slightly declined toward the central part of the bay. And as are shown in Fig. 2, the deeper the layers are, the steeper the inclination. The clayey deposits decrease in the thickness toward the uplifted area of the hills of the Plio-Pleistocene. Such inclination is significanty accordant to that of gravels on the platforms. It is due to basin building movements (or tilting movement). The correlation of the data of boreholes makes us conceive that two epoch-making ground surfaces still remain to be buried below the deltaic deposits. The Fig. 3 shows the younger buried surface which is formed during the lowering of sea-level of the last glacial age in the consideration of the radiocarbon chronology of a piece of wood on the gravels. The surface is terraced, as is shown in Fig. 3. The terrace emerges from the deltaic deposits, forming the platform, with steep cliffs, which is dotted surface of Fig. 1. The older surface below the younger is shown in Fig. 5. It cuts flat the underlying layers as shown in Fig. 2, c. The older surface is considered to be correlated with the upper platform in the plain. The clayey or silty deposits containing shells between the two gravels (Fig. 2, o) is accumulated during the transgressive period. It is the basin-building movement of the Osaka plain that preserved the old landforms in the depressed place., byburying them in the materials from the uplifting area. The late-pleistocene geomorphological process of the north-western Osaka Plain can be schematically represented as shown in Fig. 6, (I). The surface of gravels is formed in the order of I, II, III. In case the quantity of the deposits in the depressed area, is negligibly scanty, or the relative rise of sea-level is so rapid that sedimentation can not keep up with it, the scheme of it will be (II) of Fig. 6. In rapanese Islands, such tilting movement in depositional plain seems to be commen process.

THE GEOMORPHOLOGY AND THE CRUSTAL MOVEMENTS IN THE SOUTHEASTERN PART OF THE OSAKA PLAIN

The purpose of this article is to clarify the basin building movement in the Osaka Plain and it's activity, and to know the geomorphological significance through the geomorphology of the Late Pleistocene hills ;and terraces. The region with which the author mainly dealt is so narrow that an intensive study is permitted. The results brought by this investigation are expected to be suggestive and useful for further studies of the Osaka Plain in this line. With a view to studying by this way, the marked geomorphological evidences in the surrounding areas are taken account of in this discussion. Eustatic movement is considered to be negligible in the inquiry into the formation of the terraces in this plain. The terraces and the plateforms are so discontinuous and variable that they can not be brought into proper correlation. The tectonic significance in reasoning the geomorphology of the hills and the terraces is justified by the geological structure which accords to the landform. The hills and terraces in the Osaka Plain are composed of the Osaka Group, Pun-Pleistocene, which was accumulated in the Osaka Basin. The basin building movement has developed with flextures, folds, reverse faults and overthrusts. The Osaka Group abuts against the slopes of the mountains around the plain, and is folded, faulted or disturbed. Indulatory deformations of various scale, some of which areclosely connected with the structure, disturbed in one way, or modified the basin building movement ire the other way. The highest part of the hills, called the Hilly Surface in this artiele, is maintained by the uplifting structure of folds and flextures. The crustal movements indicated by the geological structure are considered to have been still active after the formation of the Late Pleistcene terraces in the southeastern region.. The geomorphological surfaces are regarded as an outcome of the basin building movement, according to which were developed the erosional surfaces in the uplifted part on the mountainous side and the the accumulative surfaces in the depressed part. The last figure (Fig. 8) schematically shows the process of the hills and terraces. The surfaces in the southeastern part of the Osaka Plain are divided into the Hilly Surface, the Kl Surface, the K2a Surface and the K2b Surface. The Hilly Surface of the most variable relief occupies the areas on the mountainous side. The height of it ranges from 80m to 200m. The K1 Surface was developed by the continuing crustal movements. It divides into the erosional surface among the Hilly Surface and the accumulative surface on the lower side. The K2a Surfsce was formed in the same manner as the K1 Surface. The fluvial terraces in the southeastern part of the Osaka Plain, almost belonging to the K2a Surface, cut through the hilly lands of the Hilly Surface and the K1 Surfaces. As with the K1 Surface, the terraces of the K2a Surface transform into accumulative surface downstream in the area with straightforward streams into Osaka Bay. The accumulative surface is slightly dissected by the K2b Surface. The Figure 1 shows the location of these surfaces.

On the Irrigation Ponds of the Osaka Plain, especially on the Kashii River Valley

The Southern part of Osaka Plain is one of the regions which has a great many irrigation ponds for paddy-fields. In many geographical writings, one often comes across the statement saying quite simply that it is because this region is an area within the Inland Sea, or the Seto-uchi region, with the least rainfall, that there are many ponds. But the authors do not agree to such an opinion. They consider the reason for the numerous ponds found in the region to be as follows: All the rivers in this region are short and have small catchment areas where there are no high mountains to cause rainfall. But the total area of paddy-field in the river valleys is large for the size of the rivers; therefore the paddy-fields of the region cannot get enough irrigation water from the river source only. In Japan, wherever river water is insufflcient, irrigation ponds or wells are made use of. So we made an inquiry as to which of the two facilities is better suited for this region. As a result of our study, we have discoveredt hat since this plain is occupied for the most part by diluvial upland with a slight gradient where the soil has small permeability, and moreover, it is surrounded by hills where there are many sites for ponds, it is easier and more advantageou to construct irrigation ponds than to dig wells. As a matter of fact, it has been found that there is need for such irrigation facilities as ponds in this region, and that the topographical features are also suited for making ponds. Hence the pond irrigation has developed. In order to work effectively, however, irrigation ponds must be easily supplied with water. But judging from map reading only there are many ponds which seem to be very difflcult to collect water. The means of collecting water seemed to be a most interesting problem for the authors; so they selected and studied three characteristic districts_??_the northern part of the region east of Sakai City, the Makio River Valley, and the Kashii River Valley. The catchment area of the northern part east of Sakai City is the smallest one on this plain, so the possibility of collecting water for the ponds is greatly limited. As a result, the farmers, when transplanting rice, must wait for the rain of the so-called “bai-u” or the rainy season, which begins from between the 10 th to the 20 th of June and lasts until the 1 st to the 10 th of July. In the Makio River Valley, the river and ponds co-operate to supply irrigation water. In the Kashii River Valley, there are three characteristic areas. One is preferentially supplied with water from the ponds in the hill-land which easily gather river water ; the second is supplied with water from shallow, dish-like ponds on the plain where it is difficult to gather water ; and the third utilizes under-ground water and river water in addition to pond water.

ON THE GEOGRAPHICAL CONFORMATION OF INDUSTRIAL ZONES OF JAPAN

With the change of era the industrial zone has seen alternations by the influence of its nation's social economy; and its amplification tends to synthetize the zone. To prove this, firstly by apprehending the reproductive correlations, it is necessary to explain the structural factors of the zone. Consequently, the, author as to explain the geographical conformation of industrial zones chiefly, in Osaka Prefecture. The distribution of industry of Japan has its center in Tokyo and Osaka, and composes regional structure including groups of factories in satelite cities. Industrial zones belong to their respective regions and their faculties are gathered in the center. The calls this central faculty its nucleos. These nuclei are responsible for the organization of our nation's four large indus-trial zones and their marked features of distribution. The nuclei of Osaka may be considered. the nuclei. of Japan and can be classified into the follo-wing wing three types. 1. City central type-Composed of, 9 districts around I shiyama Daichi (Osaka. Castle), highly productive districts of medium and small scale .indus-tries specialized in machine tools and sundries The -chief finished product enterprises are the medium and small sized factories dealing with clothing, printing and book-binding, etc. Their diversions in. enterprise and factory site are rampant. Neverthless, the density of distribution is thickest in Japan. 2. Suburban type-Composed of 13 districts on the outskirts of (1) where numerous large scale machine, machine tool and ceramic factories: stand; and, their local transfers are rampant. The whole industry is made up of large, -medium and small' scale factories. None of these alone is, , dominating, but factories of over 200 workers are beginning to be predo-minant. 3. Satelite city-Composed of 15 cities and 7 c_??_ties (guns) scatteringly distributed over Osaka Plain. These are new-born cities and counties boo-ming with -textile industry. The number of factories is largest in the: cities of. Fuse and Sakai and in the county of N aka I awachi. Cities have a marked, feature of having greater number of factories and more efficient skilled workers than counties. This characteristic distribution can. be considered as a, . result of local diversions influenced by unclear factors. It can be. obtained by both centri-petal and centrifugal forces. That is, as can be observed in various stages, of the history of development, the former exist in the social economic and superior maintenance conditions, and the latter, in the changes in scale and system of management ensued by, the rate of industrial growth. But if we study the factors responsible for the development of zone, we. can observe that the superior topographical conditions such as port., in respect to the shipment of material and the availability of labor have a close chain like relation with the zone. And this fact clearly appears inn het cost ratio. Hence, the composition of zone is developed and: amplified by its nucleus-in the center. Predominance. in production has been. brought about by the influence of both centripetal and centrifugal factors, . and has formed local.. characteristics. Fut., since, in general, the movement towards heavy che-mical industry can be noted in the constant changes of local conditions, it is necessary to improve the quality of topographical conditions based on this movement.