著者

吉野 正敏

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.100, no.6, pp.891-909, 1991-12-05 (Released:2010-02-25)

参考文献数

87

被引用文献数

3 3

著者

鹿園 直建

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.111, no.3, pp.360-373, 2002-06-25 (Released:2009-11-12)

参考文献数

31

被引用文献数

1

---

Previous studies such as that of Meybeck (1987) estimated the CO2 flux from atmosphere to riverwater due to chemical weathering by assuming that the rate of weathering of silicate rocks and carbonate rocks is proportional to the surface areas of rocks (silicate rocks : carbonate rocks = 7 : 3). However, the dissolution rate of carbonates (calcite and dolomite) is in two to four orders of magnitude higher than silicate (feldspar). This may imply that Meybeck's and other previous approaches lead to a large uncertainty in the estimate of CO2 flux. However, their estimates are nearly similar to that of Gaillardet et al. (1999), who estimated the contribution of the weathering of silicates and carbonates to riverwater chemistry based on a large volume of analytical and runoff data of the world's 60 major rivers.The thermochemical calculation in the present study indicates that the chemistry of riverwater having a small runoff is controlled by the solubilities of calcite and Na ·Ca-feldspar (Na : Ca = 1 : 1) at atmospheric PCO2 (10 -3.5 atm) and the world-wide average riverwater chemistry plot is close to the Na ·Ca feldspar-calcite-riverwater equilibrium point. This result reasonably explains the similar estimated values of CO2 flux obtained by Meybeck (1987) and others and Gaillardet et al. (1999).The conditions for riverwater saturated with Na ·Ca feldspar and calcite were derived based on a dissolution kinetics-fluid flow coupling model and were expressed as functions of τ (residence time of groundwater) and A/M (A : surface area of mineral, M : mass of water).

著者

松野 太郎

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.100, no.6, pp.881-890, 1991-12-05 (Released:2009-11-12)

参考文献数

6

被引用文献数

1

著者

浅川 忠

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.102, no.6, pp.708-714, 1993-12-05 (Released:2010-11-18)

参考文献数

18

著者

萩原 幸男

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.101, no.6, pp.421-429, 1992-12-05 (Released:2009-11-12)

参考文献数

27

著者

藤井 理行

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.98, no.5, pp.535-561, 1989-10-25 (Released:2011-02-17)

参考文献数

53

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In recent years it has become obvious that two large ice sheets in Antarctica and Greenland are most ideal medium for past some 100k year record of global climate and environment. Compared with deep-sea sediment, polar ice core has some following advantages as record medium for palaeo-environment.1) High resolution because of high accumulation rale, 2) High Accurcay because of inactive chemical at ice sheet surface, and3) Occulusion of air itself by the process of densification from firn to ice.Recent polar ice core studies have revealed 100 k-year cycle of climatic change and the synchronism between Northern and Southern Hemisphere. French and Soviet co-studies on Vostok ice core suggest that CO2 change have had an important climatic role during the late Pleistocene in amplifying the relatively weak orbital forcing. Thus ice core studies have provided fundamental information for the interpretation of glacial and interglacial climatic cycle. Furthermore, such studies on long term climatic changes basis on ice cores show the necessity of interdiciplinary interpretation on atmosphere-ocean-cryosphere climatic system and its relation to earth's orbital movement.Climatic cycle shorter than 100k-year shows regional characteristics. Hypsithermal, the warmest thousand years in Holocence appears in different ages; 8, 000-4, 100 years B. P. for Camp Century, Greenland core, 8, 000-4, 500 years B. P. for Byrd core, (9, 000)-5, 000 years B. P. for Mizuho core and 11, 000-8, 000 years B. P. for Dome-C core, Antarctica. So dose “little ice age”, the recent cold centuries. Polar ice cores reveal large volcanic eruption. Recent studies have suggested the climatic role of volcanic activities; The acidity of Byrd core indicates that a major volcanic event occurred for 150 years just when the transition period from the late glacial to the Holocence started.Thus polar ice core studies release valuable informations on palaeo-climate and environmont. However, further studies are requested for the detailed, quantitative and interdiciplinaly interpretation of 102-105 year climatic variation with high quality deep ice cores. Japanese Antarctic Dome Program at the top of Dronning Maud Land, Antarctica and European Greenland Ice Program (GRIP) are expepected to provide by-polar “standard” cores which will cover more than last climatic cycle.

著者

石田 瑞穂

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.96, no.4, pp.209-222, 1987-08-25 (Released:2009-11-12)

参考文献数

23

---

The occurrence of large earthquakes in the Kanto-Tokai (K-T) district has been interpreted by the interaction among the Philippine Sea (PHS), the Eurasian (EUR) and the Pacific (PAC) Plates the PHS and PAC plates underthrust beneath the EUR plate in this region. In order to understand the tectonic process taking place beneath the K-T region, the seismic activity, velocity structure and source mechanisms were studied by using the data from recently developed seismological observation networks. The double-planed structure of the intermediate-depth seismic zone was observed clearly beneath the Kanto districts, and the PHS plate underthrusting from the Sagami and Suruga troughs were clearly delineated by the high velocity and high seismic region. The distribution of pressure axes corroborated the results derived from the hypocentral distribution.

著者

鈴木 舜一

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.110, no.5, pp.734-743, 2001-10-25 (Released:2009-11-12)

参考文献数

36

被引用文献数

2

著者

小出 仁

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.116, no.2, pp.294-296, 2007-04-25 (Released:2009-11-12)

参考文献数

11

被引用文献数

1

著者

遠藤 毅

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.115, no.4, pp.500-507, 2006-08-25 (Released:2009-11-12)

参考文献数

19

被引用文献数

1 1

---

Modern manufacturing factories in the Tokyo Lowland-the developing eastern part of Tokyo Metropolis-were originally constructed by the national government at the beginning of the Meiji era in about 1870. Subsequently, the area developed as one of the important industrial areas in Japan. In particular, industrial development was remarkable during the period from about 1950 to about 1960. However, this extreme industrial development brought overpopulation and public nuisances such as air and noise pollution and vibration from plants and manufacturing sites in the Lowland. To ease this serious situation, the national government and the Tokyo metropolitan government took measures such as restricting construction of new factories and strengthening regulations on the operation of factories.Through these measurements, the increase of manufactories in the area stopped in about 1955, and many have disappeared since about 1960 because of their transfer to other cities or manufacturing operations shutting down.According to this investigation, many sites of factories and warehouses had their use diverted by citizens to facilities such as condominiums, general residential areas, parking lots, schools, and parks. In particular, conversion to residential use has been remarkable.

著者

久田 英子

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.110, no.1, pp.1-16, 2001-02-25 (Released:2009-11-12)

参考文献数

103

---

The Vredefort Dome, located in the central part of the Witwatersrand Basin in South Africa, is the type locality for pseudotachylite. Pseudotachylite at the Vredefort Dome is generally regarded to be of impact origin. Pseudotachylites which are closely associated with faults are, however, also known to be common along the northern and northwestern edges of the Witwatersrand Basin. In order to compare pseudotachylites from the Vredefort Dome and from the surrounding Witwatersrand Basin, different studies were undertaken in the past. Mode of occurrence, microscopic textures, geochemical analyses and chronological measurements of pseudotachylites are briefly reviewed in this paper.In the Vredefrot Dome, pseudotachylites are commonly observed except in the central part of its core. In the surrounding Witwatersrand Basin, they are reported from drill core sections and in underground workings. The matrix in pseudotachylite from the Vredefort Dome is mostly a recrystallized melt phase, while those from the surrounding Witwatersrand Basin seem to be composed of clastic material. Pseudotachylites both from the Vredefort Dome and the surrounding Witwatersrand Basin are geochemically closely related to their host rocks. Although evidence for more than one generation of pseudotachylite has been presented, both in the Vredefort Dome and the surrounding Witwatersrand Basin, it is widely believed that most of them were formed as a result of the Vredefort impact event (ca. 2.0 Ga). Other fault rocks reported from the surrounding Witwatersrand Basin are older than the pseudotachylites and therefore not related to their formation.

著者

武永 健一郎

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.77, no.1, pp.37-55, 1968-02-25 (Released:2009-11-12)

参考文献数

63

被引用文献数

2

---

The purpose of this paper is to classify low-altitude erosional surfaces in Japan and also to investigate the characteristic features of the granite mountains.Mt. Suzugamine at the western part of Hiroshima city is consisting only of granite. The geomorphic surfaces of Mt. Suzugamine are classified roughly into two, Higher-Setouchi surfaces and Lower-Setouchi surfaces. Yamada surface of the Plio-Pleistocene in origin and Piedmonttreppen belong to the former and gentle slope remnants of early-middle Pleistocene and “Kannon surface” of middle-late Pleistocene belong to the latter. Neither marine terraces nor tephra are found in this area. As a result, it is difficult to correlate these with the geomorphological surfaces elsewhere which have already been well examined.The gentle slopes were formed by the removal of deeply weathered granitic top soils about 50 m in thickness and the climatic change seemed to be less active.Landforms were modified even in Würm glacial period as was seen in the “Kannon surface”. The agencies which formed the initial gentle slope is similar to one which formed “Kannon surface”.Suzugamine mountains, which consists of granite, is characterized by gentle slope, box valley, earth fall, block stream, wide-opening valley and inward-opening valley. I should like to propose to term such geomorphology “granite topography”. It may be seemed that downwarping movement toward the Inland Sea (Setonaikai) has lasted down to the Pleistocene period, on the ground that the upper streams running down northward were captured by the ones running down southward.

著者

栗谷 豪

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.116, no.1, pp.133-153, 2007-02-25 (Released:2010-02-25)

参考文献数

103

被引用文献数

1 2

---

Water has been continuously degassed from the Earth's interior by magmatism throughout evolution, and can significantly affect dynamic processes of its carrier, i.e., magmas, during their transport from the mantle to the Earth's surface. This paper summarizes the effects of water on the physical and thermodynamic properties of magmas, and their roles in magmatic processes. Magmas commonly contain at least 0.2 wt.% of water, and some magmas can have up to 6 wt. %. Despite the fact that water is a minor component in silicate liquids, the effects of dis-solved water on the properties of silicate melt are significant because it has a much lower molecular weight at 18.0 than those of the other components (SiO2. 60.1, for example). Dissolved water greatly affects the density and the viscosity of silicate melts, thereby controlling rates of dynamic processes of magmas, such as segregation of primary melts in the mantle, transport of magmas from the mantle to the crust, convections and crystal-melt separation in crustal magma chambers, and ascent of magmas in volcanic conduits. Water also influences solid-melt thermodynamic equilibrium relationships, and this affects the chemical differentiation paths of magmas, in addition to the amount of melt production in the mantle by changing solidus temperatures. The eruptive behavior of volcanoes is driven by the exsolution of magmatic water, and as such depends on the water solubility of magmas mainly as a function of pressure. Water has also played important roles in the evolution of the Earth. Magma generation has been induced by water in the Earth's interior, and magmas have carried materials and energy from the interior to the surface of the Earth. In particular, water transport beneath an island arc is important in the global water cycle, and has greatly affected the environment of the Earth's surface.

著者

藤原 治 小松原 純子 高田 圭太 宍倉 正展 鎌滝 孝信

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.115, no.5, pp.569-581, 2006-12-25 (Released:2009-11-12)

参考文献数

36

被引用文献数

9 9

---

The temporal development of a late Holocene strand plain system along the western Shizuoka Prefecture was reconstructed based on facies analyses and 14C dating for core samples excavated in a back marsh using a geo-slicer, 6.0-m-long, 0.35-m-wide, and 0.05- to 0.1-m-deep wedge-shaped stainless steel case. The strand plain system consists of beach, sand dune, and back marsh. Stratigraphic succession of the strand plain system, up to 4.4 m thick, is composed of upper shoreface sand, foreshore sand, backshore sand, and back marsh mud, in ascending order. The succession shows three development stages of the strand plain system.Stage 1 (before the 13th century) : The study area was under a wave-dominated beach environment. The beach system was developed by progradation of shoreface, foreshore, and backshore deposits in the later period of this stage.Stage 2 (from the 13th century to the 16th century) : Sand dune and back marsh developed, covering the beach deposit. Humic mud was thickly deposited in the back marsh with low sand supply from seaward across the dune.Stage 3 (after the 17th century) : The back marsh has been infilled mainly by washover sand and debris from the hinterland. The AD 1707 Hoei Earthquake Tsunami, which destroyed villages on the dune, possibly promoted reactivation of sand movement from ruined dune to the back marsh.

著者

長岡 信治

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.97, no.3, pp.156-169, 1988-06-25 (Released:2009-11-12)

参考文献数

28

被引用文献数

4 2

---

The Kikai caldera volcano located under water in East China Sea is one of the most gigantic calderas in southern Kyushu. At the caldera, a violent eruption occurred from the submarine vent, at ca. 70-80 ka. The eruption is interpreted to have been phreatomagmatic throughout. Each eruptive phase of the eruption sequence generated its own characteristic deposits. The sequence of the events can be summarized as fallows ; (1) a small phreatomagmatic eruption, which generated the fine grained ash including accretionary lapilli, (2) the catastrophic pyroclastic-flow eruption, which formed a large-scale pyroclastic flow (the Nagase pyroclastic flow), two pyroclastic surges (Nishinoomote-1 member : Ns-1, Nishinoomote-3 member : Ns-3), and a wide-spread co-ignimbrite ash fall (Nishinoomote-2 member : Ns-2).The Nagase pyroclastic flow came down from the rim of the caldera, and entered the sea. Then, the flow body, which included a large amount of large pumice blocks and heavy lithic fragments, was disintegrated as gas-particle flow by violent phreatomagmatic explosions, or continued subaqueously as water-supported mass flow. Dilute and fine-particle-rich pyroclastic surges, probably with a density much less than that of water, 1.0 g/cm3, generated off the top or head of subaerial Nagase pyroclastic flow. They could cross on the smooth surface of the sea, becoming water-cooled, vaporish and depleted in large clasts which dropped into the sea. Eventually, the cool and wet pyroclastic surges attacked the islands around the caldera, and deposited as Ns-1 and Ns-3.Ns-2 co-ignimbrite ash fall, composing of glass shards were generated from the upper convective part of the eruption column of the Nagase pyroclastic flow. Included accretionary lapilli indicate that the eruption column was very moisture because of much sea water flash-out subaerially for very violent explosions from the submarine vent. Ns-2 is probably correlated with the Kikai-Tozurahara ash which was found in central Japan more than 500 km off the source.

著者

米倉 伸之

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.77, no.1, pp.1-23, 1968-02-25 (Released:2009-11-12)

参考文献数

34

被引用文献数

14 11

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The Kii peninsula, located on the Pacific coast of central Honshu, is fringed with coastal terraces in its southern part, while its east and west coast are characterized by ria shorelines. The purposes of this paper are to clarify coastal development of the peninsula, especially the history of vertical changes in sea level in its coastal region, and secondly, to examine the relation between the mode of Quaternary crustal movement (especially its vertical component) and recent crustal movement associated with contemporary seismic activity.Coastal terraces and an interpretation of their developmentCoastal terraces, developing along the southern coast of the Kii peninsula (Fig. 2), are mostly rocky abraded terraces covered with thin marine beds. In the northern part of the east coast (north of Shingu) and at the mouths of some rivers, however, some marine terraces are composed of marine sediments overlying fluvial beds. The coastal terraces are classified into two levels of the high and low terraces in the surroundings of Shingu, where they are typically developing (Fig. 4). Both levels of the terraces are further subdivided into some sublevels which are dentoted by H1, H2, H3 and H4 in the high terraces and L1, L2 and L3 in the low terraces respectively in the descending order. The height of each sublevels at Shingu are 125, 113, 95, 61, 49 and 39 meters above sea level. The highest terraces H1 are dissected into narrow hill ridges, overlaid by round gravel beds more than 20 meters thick. The H2, H3 and H4 terraces are rocky abraded ones. The most extensively developing terraces Li are composed of marine sediments underlaid by fluvial beds more than 40 meters in thickness. The L2 and L3 terraces are marine or fluvial terraces which have been formed cutting down the L1 terraces. Alluvial plains (denoted by A) do not so extensively develop along the coast, except at the mouths of the rivers. Judging from some boring data, alluvial formations at the mouths of the rivers are more than 30 meters thick (Fig. 3). From these facts it is concluded that the Hi and Li terraces and alluvial plains are depositional surfaces composed of thick marine and fluvial deposits, which are filling submerged fluvial valleys and, therefore, that the coastal region, being interrupted by temporary submergence, has been emerged in precess of the formation of the coastal terraces. The other terraces H2, H3, H4, L2 and L3 have no feature indicating submergence and, therefore, are considered to have been formed in process of emergence. Judging from the thickness of deposits, amplitude of submergence during the later two periods is considered to be greater than that during the previous period.As to the process of formation of alluvial plains, rapid submergence of this period is regarded in another regions as being largely due to eustatic rise in sea level caused by world deglaciation from the results of the researches on submerged topography, marine topography, succession of alluvial formations, absolute age determination of alluvial marine beds, climatic changes and etc. The process of formation of alluvial plains in the Kii peninsula is inferred to be the same as in another regions from the submerged fluvial valleys and the thickness of alluvial formation and, therefore, the submergence during the last period was caused by eustatic rise in sea level.

著者

高木 圭介 青池 寛 小山 真人

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.102, no.3, pp.252-263, 1993-06-25 (Released:2010-10-13)

参考文献数

42

被引用文献数

2 3

---

A synthesis of geological, geomorphological, and petrological data was made to reconstruct the tectonic evolution of the collision zone between the Honshu and Izu-Bonin Arcs during the middle to late Miocene time. The collision zone is composed of four allochthonous terranes, which are overlaid by syn-collisional trough-filling deposits. The four terranes, Izu, Tanzawa, Misaka, and Koma Terranes, were originated in the Izu-Bonin volcanic arc and have in turn collided with and accreted into the Honshu Arc at about 1, 5-3, 11, and 15 Ma, respectively. The geomorphology of the northern part of the Izu-Bonin Arc is characterized by two N-S trending ridges, Shichito-Iwojima and Nishi-Shichito Ridges, and Nishinoshima Trough between the two ridges. We interpret the Nishi-Shichito Ridge as a remnant volcanic arc of early Miocene age. The Nishi-Shichito Ridge was left by backarc rifting, which occurred between the Nishi-Shichito and Shichito-Iwojima Ridges during 15-10 Ma. The backarc rifting resulted in the increase of downdip angle of the Pacific plate slab and the eastward migration of the Izu-Bonin volcanic front. The rifting also generated along-arc compressional strain, which caused the intraarc deformation of the Shichito-Iwojima Ridge at about 10 Ma. This interpretation well explains the geologic history of each allochthonous terrane in the collision zone between the Honshu and Izu-Bonin Arcs as well as the present distribution of the allochthonous terranes.

著者

安藤 寿男

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.99, no.3, pp.247-262, 1990-06-25 (Released:2009-11-12)

参考文献数

49

被引用文献数

1

---

The depositional sequence concept was established in newly developed sequence stratigraphy, as an unconformity-bounded stratigraphic unit formed during one complete sea-level cycle. This paper reviews general meanings of “sequence”, the definition of depositional sequences, their hierarchial patterns and recognition, and sequence boundaries problems, from a viewpoint of sedimentary geology based on outcrops and bore-hole samples.Though the word, “sequence” has many meanings generally applied to successive geologic events and processes in chronologic order, a depositional sequence is defined in a special sense, as “a relatively conformable succession of genetically related strata bounded at its top and base by unconformities and their correlative conformities”. The depositional sequence as one of hierarchial transgressive and regressive units (T-R units), has the first- to forth-order operational units, that is, the megasequence, supersequence, sequence and parasequence in descending order. A sequence boundary with a significant hiatus (=unconformity) is formed by subaerial exposure, concurrent subaerial erosion and partly submarine erosion during eustatic falls or low-stand sea level.The latter half of this paper emphasizes the difference between sequence boundaries and ravinement surfaces. The ravinement surface formed as one of diastems or “transgressive surfaces”, is an erosional surface by shoreface retreat during the following transgression after a sea-level fall. In general, it is lithologically more distinct than the underlying sequence boundary. The right recognition of the difference leads correct reconstructions of sedimentary history.

著者

橋本 学

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.111, no.2, pp.298-307, 2002-04-25 (Released:2009-11-12)

参考文献数

20

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We attempt to simulate the activity of earthquakes of moderate to large sizes in and around the Japanese islands using a block and fault model, in which slip deficit rates were derived from triangulation and trilateration data covering one-hundred years. The original block and fault model has 104 faults. However, the original fault size is too large to simulate moderate earthquakes. Therefore, we divide each modeled fault into 5 × 5 elements to generate earthquakes as small as M5. In total there are 2600 elements. We assume stress accumulates according to the estimated slip deficit rates. Interaction between fault elements is represented by changes in Coulomb Failure Function (hereafter Δ CFF) induced by the movement of other faults that are determined by the geometrical relationship and the direction of slip deficit rates. When stress reaches the threshold level, accumulated CFF is released by a forward slip and redistributed to surrounding faults according to the CFF changes calculated above. If the redistribution of CFF induces the next rupture, the same process is repeated until there are no more rupturing elements. We assume rupture thresholds to be 2.5 MPa for interplate boundaries and 10 MPa for inland faults, respectively. We simulate seismicity for 10000 years with a time step of 1 year.In this simulation large events that rupture almost all elements of a fault rarely occur. This suggests that strain rates derived from geological data or historical earthquake catalog might be underestimated. Simulated seismicity does not satisfactorily fit the GutenbergRichter's law, because moderate events occur more frequently than small or large events. This suggests that we have to incorporate heterogeneity in the rupture threshold or the size of elements on a fault plane. The correlation between interplate earthquakes along the Nankai trough and inland events in southwest Japan is not clear, but there seems to be a complementary relationship in activities between both regions. Migration of large events along the Nankai trough is occasionally seen in this simulation, but its direction is different from time to time.

著者

古田 俊夫 中西 正男

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.99, no.5, pp.490-506, 1990-10-25 (Released:2010-10-13)

参考文献数

59

---

The discovery of the magnetic anomaly lineations that can give ages of ocean floor is a very important role for establishment of the plate tectonics theory. The magnetic anomaly lineations also give us information of a history of movements of the oceanic plates. However, the origin of magnetic anomaly lineations still been obscured, that is, we can not clearly answer for the following questions: How thick is the source layer of magnetic anomaly lineations? How strong is the intensity of the magnetic source layer? In this paper we examined the relevant information concerning the magnetization of the oceanic crust from studies of observed marine magnetic anomalies and from rock -magnetism of oceanic basalts to get a goal of these questions in this paper.The skewness parameter that is deduced by precise magnetic anomaly lineations is important to identify marine magnetic anomalies. The magnetic polarity transition width is also important to do, though the parameter associated with this transition width has not almost utilized in the previous works. The anomalous skewness and the skewness discrepancy are often observed over the oceans. These observations might be explained not by a single-layer model but a two-layer model for magnetic source layer. The polarity transition width is defined the width which 95.4 % of the change from normal to reversed polarity occurs within. This width increases monotonically with spreading rates of ridges and/or with ages of ocean floors. This increasing is considered to be a manifestation of a more complicated crustal source consisting of two discrete layers. The analysis of the skewness parameter and transition width strongly supports that the sourc elayer of marine magnetic anomalies has a two-layer structure. The upper layer, consisting of surface lava flows of layer 2 A and possibly the sheeted dike complex, hasdi stinct and approximately vertical magnetic in the vicinity of opposite magn etized region boundaries. The lower layer, consisting of intrusive and gabbroic layers, has the boundaries gradually sloping downward away from the spreading center.Many detailed survey are carried out to reveal the structure of magnetic source layer by the multi narrow and the deep-towed magnetometer near active ridges. Inversion of magnetic layer using results of detailed surveys concluded that the magnetic source layer near the active ridges is less than 1 km in thickness. The polarity transition width of the relatively young layer is narrower than that of older oceanic floor, and the magnetic intensity of the relatively young layers higher (more than 10A/m) than that of older one. These conclusion indicate that the magnetic source layer near the active ridg es consists of a single layer structure. It is thought that the magnetic source layer grows with ages asoceanic crust by results of analysis of skewness and polarity transition width and inversion of magnetic source layer near active ridges.Several previous paleomagnetic studies indicate that intensity of natural remanent magnetization (NRM) of basaltic rocks composing the ocean crust rapidly decreases with ages in the past 10 to 20 Ma, and gradually increases older one. This change in NRM intensity is roughly proportional to the changes in intensity of saturation magnetization of the rocks and possibly due to sea-water alteration (low-temperature oxidation) of the primary ferromagnetic minerals contained in the rocks. NRM of the oceanic rocks is initially thermoremanent magnetization acquired at the time of formation of the oceanic crust. In accordance with progressive oxidation, fraction of TRM to bulk intensity decreases, while that of the secondary magnetization increases.