In the southern part of the Kitakami Mountainland, North-east Japan, the Permian-Triassic boundary is often well exposed, where the Upper Permian Toyoma Slate and the Lower Triassic basal member of the Inai Group are intimately associated. There, T. Kobayashi once inferred the Tate epeirogeny and later Y. Onuki the Otani orogeny at the Permian-Triassic interval. N. Kanbe who dealt with the gradual transition between the topmost Permian and basal Triassic limestones in Kyûusyû, stated, referring to the Permian-Triassic boundary in the Kitakami Mountainland, “the crustal movement occurred at the Permian-Triassic transition was no more than gentle undulation, although erosion took place at emerged part”. On the other hand, F. Ueda. after his many years' field studies. declared in his paper. “The geological structure of the Permian and Triassic in the Toyoma and Maiya district, southern Kitakami Massif, North-east Japan” (in Japanese), 1963, that he could trace a fairly large overthrust sheet of Permian formations in the Toyoma-Maiya district, Tome-gun, Miyagi Prefecture, along the east side of the Kitakami-gawa. The Permian system of the district, approximately trending N-S, consists of, in descending order Toyoma Slate, lacking fusulinids, Yamazaki Conglomerate (Usuginu Conglomerate), Yabeina zone, Tenzinnoki formation, Parafusulina matsubaishi zone (corresponding to the Neoschwagerina-Verbeekina zone of the other regions in Japan), Nisikori formation, upper part, Parafusulina zone, lower part, Pseudoschwagerina zone. His geological and tectonic maps (Pls. I, VII) show the overthrust sheet built essentially of Upper (eastern) layer of the Toyoma Slate, Middle (intermediate) layer of the Yamazaki Conglomerate, Lower (western) layer of the Yamazaki Conglomerate and Tenzinnoki formation closely folded together. The upper layer, the Toyoma Slate, is unconformably overlain by the Hineusi formation thought to be contemporaneous with the Lower Triassic Hiraiso formation of the Inai Group ; the boundary of the two formations is said to be strongly undulated, indicating an intense erosion interval. The boundaries on the maps, between the overthrust sheet and its superjacent Hineusi formation and subjacent foundation structure, as well as these between its three component tectonic layers are parallel to each other in broad sense, though variously undulated in themselves. The foundation of the overthrust sheet is built of the Nisikori, Tenzinnoki, and Yamazaki formations ; these formations are closely folded and in general overturned to east, but partly to the opposite direction, perhaps under the influence of the westward shift of the overthrust sheet. Now assuming Ueda's conception about his overthrust sheet as well established, there arises another question regarding to the geological age of this tectonic event. Ueda dated it at the Permian-Triassic interval, based on the fact that whereas the Permian system of the overthrust sheet and its foundation is extremely complicate in structure, the Triassic Inai Group is tranquil in its general behaviour. Furthermore, the tectonic lines separating six transverse segments of the overthrust sheet from each other do not extend into the overlying Triassic deposits, and there is also no trace of any significant relative shifting nor shearing between the Toyoma Slate and the Hineusi formation. There are, however, certain geological features incongruent with Ueda's view, mentioned below.
From the geological survey and results obtained by the grain size analyses of the sediments of the Pleistocene system distributed between Hirao and Ishiyama, the writer has drawn the following conclusions on a part of the uppermost Kobiwako group. 1) The Pleistocene system in this area is divided into two formations, the Kokubu (upper) formation and the Yakino (lower) formation. 2) On the triangle diagram (pebble + sand, clay and silt), the sedimentary materials of the Pleistocene system of this area are classified into six groups in the Kokubu formation and five groups in the Yakino formation. The distribution mode of grain size is given as the bimodal distribution which consists of the traction and suspension load. 3) In relation to the coefficient of sorting (So) and the medium grain size (Md), the sedimentary material of the Pleistocene system of this area is classified into six types (II, III, V, VI, VIII and IX) in the Kokubu formation and five types (II, III, VI, VIII and IX) in the Yakino formation. The writer proposes to call their grain size rank the “So-Md Rank”. 4) By plotting the medium grain size (Md) on Hjulstrom's diagram, it was clarified that Md is proportional to the settling velocity (Sv) and is in inverse proportion to the critical velocity (Cv), and also the coefficient curve of sorting is recognized as the interrelation curve between the critical and settling velocity curves. 5) The transition of the grain size type, depositional movement and index number of sedimentary facies of the Kokubu formation is conspicuous in comparison with the Yakino formation. It may be deduced, therefore, that the former is the disturbed zone nearer to the lake beach than the latter in the sedimentary environment. 6) The difference of the background between the two formations may be suggested by the difference in their sedimentary materials. 7) From the relation of “N value” and index number of plasticity, the upholding strength of each grain size type is divided into A, B and C in grade. The relation between each grade is shown as A>B≥C. 8) The rate of increase of the upholding strength of each grain size type is in inverse proportion, thus |K-r| = e. K : rate of contained water, r : index number of plasticity. 9) The strata conspicuous in the transition of the sedimentary environment may be conspicuous in the transition of the grain size type and upholding strength.
A model of the crustal structure of Honshu, Japan, deduced from the data obtained by the Research Group for Explosion Seismology is as follows : 1) The velocity of the shallowest layer is 5.5 to 5.8 km/sec and its thickness is less than several km. In some localities this layer does not exist and a layer with the velocity 6.1 to 6.3 km/sec is found just below surface layers. 2) The depth of the Moho discontinuity is about 20 km in north-eastern area, about 25 km in Kanto, and about 35 km in the central mountainous area. These values are deduced under the assumption that the crust is mostly composed of the material with the velocity of 6.1 to 6.3 km/sec. 3) The velocity of P wave below Moho discontinuity is slower than 8 km/sec. 4) According to the results obtained in the recent observations in the central and Kinki areas, a layer of about 6.6 to 6.7 km/sec exists below the layer of 6.1 to 6.3 km/sec. The part of the crust between this layer of 6.6 to 6.7 km/sec and the Moho discontinuity may have the velocity bigger than 7 km. 5) If we assume that a “hidden layer” of 6.6 to 6.7 km/sec exists in the areas described in (3), the calculated depth of Moho is about 10 to 20 percent deeper than the depth given in (3). 6) The “discontinuities” in the crust might not be so sharp as Moho discontinuity.
Several evidences are presented to support the hypothesis that the asthenosphere low velocity channel reaches to the M discontinuity in Japan. Informations from gravity, refraction and phase velocity studies are combined in a comparison of crust-upper mantle structure in Japan with those in other regions where the velocity beneath the M discontinuity is also lower than normal.
Three earthquakes in the last six years produced satisfactory records of Rayleigh waves, with periods of 20 to 40 seconds, at about 40 stations in Japan operated by the Japan Meteorological Agency. One of these earthquakes was the Samoa shock of April 14, 1957. Epicentral distance of this earthquake from Japan along a path was about 70° and the waves approached Japan along a path perpendicular to the trend of the island arc (Aki, 1960). Another was the Aleutian shock of March 9, 1957. Epicentral distance was about 35° and the waves approached Japan along a path parallel to the trend of the islands (Kaminuma and Aki, 1963). The other was the Mindanao shock of September 24, 1957. Epicentral distance was about 33° and the direction of wave approach from this shock was nearly the reverse of that from the Aleutian shock (Kaminuma, 1964). Phase velocities for different regions in Japan were determined by the method of least squares applied to the arrival times of selected wave peaks at several stations within each region. In determing the crustal thickness from the phase velocity, we used the phase velocity curves of Aki's model 6EJ. This model modified Press' model 6EG in such a way that the velocities were uniformly reduced by 5.5 %. The crustal thickness of each region determined by using the three earthquakes are compatible within a limit of probable errors in most regions. But in the Chubu region, the phase velocity of Rayleigh waves propagated parallel to the trend of Japanese Islands is 4 % greater than that for the perpendicular path. A map of crustal thickness in Japan is drawn by using the phase velocity data of Rayleigh waves from the Samoa, Aleutian and Mindanao shocks as shown in Fig. 5.
As the present crustal structures have been formed by the tectonic movements through the long geological age, problems of the crustal movements must be studied in connection with the information of the present crustal structures obtained from geological, geomorphological and geophysical methods. In this paper, the relation between the crustal structures and the crustal movements in Japanese islands found by geodetic methods is investigated from the following three points. 1) The relation between the changes of the intensity of crustal movements with time and those in space. 2) The relation between the horizontal variations of the crustal movements and crustal structures. 3) The difference of the characteristics of the crustal movements in orogenic regions (Japanese islands) and in continental platform.
Most probable depth of the Moho discontinuity in Japan is determined mainly from the gravity analysis. Comparison of the results with other inferences from explosion and surface wave studies indicates the lower value of P and S waves in the upper mantle in Japan. This reduction in the seismic wave velocity may be attributed either to increase in the Poisson's ratio due to the temperature effects or to elastic anisotropy of rock-forming crystals which must await further studies.
Results of terrestrial heat flow measurements so far made in Japan are briefly reviewed. As seen in the figure 1 in the text, it has been established that the heat flow distribution is quite distinct in and around Japan. On the whole, the high heat flow region coincides with the Cenozoic volcanic region in the area, i. e. the Japan Sea side of the Honshu arc and the low heat flow regions lie on the Pacific Ocean side. The pattern of heat flow distribution seems to have important bearings with many other geological and geophysical aspects of the Japanese islands. A tentative picture of the state under Japanese area is presented based on the mantle connection hypothesis.
A regional development is not the sole problem of a science or of a technology, but a comprehensive and cooperative work of various scientific fields, technology, and administration. Geography, as a science of region, has the responsibility for offering basic ideas and techniques of research, including mapping of the area confronted. It aims at the development of human life with higher income and better social services ; that is, the most important consideration is the development of spiritual-physical ability of inhabitants and to know that any economic development is the tool for human progress. Geographers will participate in a project with basic survey methods, analyzing the regional structure and relation of regions. Though actual aims of development would be much different by each regions, one of the most up-to-date ones in Japan is the adjustment of town and country inconsistency, or more strictly speaking, to find the solution of regional economic and social differences between overcrowded metropolitan areas, such as Tokyo and Osaka, and depressing countrysides with smaller towns, in a high national economic growth. Hokuriku, to which Toyama district belongs, is one of the low developed regions, compared with the Pacific coast. Long winter with heavy snow and remoteness from the metropolitan cores have prevented its economic growth. After the World War II, Japanese government took the policies of regional development of which objects have been changed by periods. (1) 1946-49. Under military occupation and devastation by the War, urgent land exploitation was taken place to settle unemployed people and to supply food. This policy was nearly unsuccessful, as most of the reclaimed land were poor in natural conditions, bad in accessibility, because of low standard of agricultural techniques of new settlers, with insufficient fund and equipments. (2) 1950-55. Japan has recovered the self government and the break-out of the Korean War, followed by the reconstruction of manufacturing industries and War-damaged cities. The integrated regional planning was established for 19 districts and Hokkaido, with the aims to improve the use of natural resources, to control floods and other damages, to increase food and other primary industrial products, to reconstruct manufacturing industries and improve social welfare. TVA was one of the most brilliant examples. These items of planning had been done separately by each governmental 'sections or by each prefectures, but the new plans seemed to be regionally integrated and districts were delimited by natural regions, such as drainage area, mountains, islands and etc. Until 1961, 850 billion yen (2.36 billion US dollars) were spent and 86 % of estimated projects were completed, as the Government reported. In fact, a considerable progress has been made, but still regional income difference was not overcome. Also, integrated program was poorly executed. (3) 1956-present. Industrialization and metropolitanization have been accelerated.Especially, in Tokyo metropolitan area, population has increased rapidly, which has resulted in a shortage of public facilities, such as water supply, transportation, and housing. In 1955, the Capital Region Project, which covers the circle with 100 km radius from the centre of Tokyo, was started. The Greater London Plan was its precedent. The project is under way, but it has a great difficulty of abrupt rise of I land price and ever increasing population, business concentration, and suburban sprawl.