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

---

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.

著者

浜野 洋三

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.430-441, 1992-12-05 (Released:2009-11-12)

著者

高畑 直人 尾上 哲治 佐野 有司 磯﨑 行雄

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.128, no.4, pp.667-679, 2019-08-25 (Released:2019-09-20)

参考文献数

27

被引用文献数

5

---

It is important to know the influx of extraterrestrial material on old Earth in order to understand global environmental changes. Helium is suitable for detecting extraterrestrial material in marine sediments, as well as platinum group elements, because there is more helium in extraterrestrial matter than on the Earth's surface. Extraterrestrial material is detected in old sedimentary rocks collected from a Permian/Triassic (P/T) boundary section in the Mino Belt, central Japan, which accumulated in a deep seafloor environment in the ancient Pacific Ocean. Much higher 3He/4He ratios (up to 150 Ra; 1 Ra = the atmospheric ratio) are observed in the samples. These high 3He/4He ratios may infer the existence of extraterrestrial helium carried in fullerenes or interplanetary dust particles. Moreover, the distribution of 3He concentrations indicates a significant increase in the influx of extraterrestrial material before the P/T boundary, which is equivalent to the influx at the Cretaceous/Paleogene boundary, because of the long duration. This increase may have caused global cooling leading to mass extinction.

著者

寿円 晋吾

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.75, no.5, pp.266-281, 1966-10-25 (Released:2009-11-12)

参考文献数

34

被引用文献数

1

著者

目代 邦康

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.121, no.2, pp.367-383, 2012-04-25 (Released:2012-05-29)

参考文献数

99

被引用文献数

1 2

---

IWATA Shuji and KOIZUMI Takeei initiated Japanese geoecology studies in the 1970s. The Colloquium of Cold Region Landform (Kanrei Chikei Danwakai) contributed significantly to Koizumi's studies. Early geoecological studies have been classified into two categories: analysis of landscape structure and research on phytogeography. The former is similar to the general system theory. This concept is a good method for understanding the natural landscape and for resolving regional issues. The latter relates to systematic geography. These studies are mainly conducted in mountain areas. While studies on natural environments in mountain areas have advanced, Japanese geoecological studies seem to have focused on special areas. Furthermore, research trends of Japanese geoecological studies were analyzed by examining competitive funding practices. The results illustrate that there have been three types of study since the 1980s: (1) phytogeographical studies and analysis of the landscape structure in cold regions such as polar and high mountain areas; (2) comprehensive geographical overseas studies; and, (3) problem-solving research on regional issues such as resource management and countermeasures for natural disasters. Currently, phytogeographical studies and problem-solving research are advancing. However, Japanese geoecological studies have not appealed to researchers in different fields until now. The future development of geoecological research requires interdisciplinary research.

著者

荒川 秀俊

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.65, no.1, pp.55-56, 1956-01-30 (Released:2009-11-12)

参考文献数

1

被引用文献数

1 1

著者

盛谷 智之

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.87, no.4, pp.181-200, 1978-08-25 (Released:2009-11-12)

参考文献数

40

---

Ocean floor manganese nodules have attracted worldwide attention as the possible future resources. However, many problems in the distribution and origin of the nodules remain still unsolved, because of the lack in reliable seabed information. Thus, several leading ocean-oriented countries are now carrying out, or have plans about the systematic research programs on manganese nodules, including both prospectings mainly by industry groups, and scientific studies by the governmental and university groups, in which the results of the latter scientific studies are expected to serve as the guideline for the former prospectings. The representative programs are as follows : In Japan, “Basic researches on the deep sea mineral resources” is being conducted by the Geological Survey of Japan, for the northern Central Pacific Basin, using R/V Hakurei-Maru (1, 821 tonnage), with participation of the NIPR (National Institute for Pollution and Resources) in each cruise on their own program, “Technological study on the development of deep sea mineral resources”. Also, the industries group, DOMA (Deep Ocean Minerals Association), is engaged in a program of “Development of new prospecting technology for manganese nodule deposits”, with the objective areas south of Hawaii Islands of the Pacific.In the United States, there are three categories of research programs, being actively conducted by the groups of universities, Federal organizations, and industries respectively. The first is “MANOP (Manganese Nodule Program) of NSF (National Science Foundation) Seabed Assesment Program, carried out by the interuniversities group. This is now concentrated on the detailed studies of the sea floor to obtain its real physical, geochemical and biological informations by means of the in-situ measurement instruments, deployed in each representative area of different sedimentological condition of the Pacific. The second is “DOMES (Deep Ocean Mining Environmental Studies)” of the Office of the Marine Minerals, NOAA (National Oceanic and Atmospheric Administration), in which the research groups from the Federal organizations such as NOAA and U.S. Geological Survey are in charge of conducting its geological aspects. The third are the programs of the industry groups related to the commercial development of manganese nodules, including prospecting, mining and processing. Four major international consortiums, Deepsea Ventures Group (OMA, Ocean Mining Association), INCO Group (OMI, Ocean Management Inc.), Kennecott Group (Kennecott Exploration), and Lockeed Gr oup (OMC, Ocean Minerals Co.) are now developing their programs, aiming at mining operation tests in the Pacific as immediate objectives.In West Germany, a program, “Researches on manganese nodules”, is actively promoted under the coordination and sponcering of the Ministry of Research and Technology, with participation of the Federal Institute for Geoscience and Natural Resources, universities and industries association (AMR, Arbeitsgemeinschaft meerestechnisch gewinbare Rostoffe), using R/V Valdivia (1, 317 tonnage), for the objective areas between Clarion and Clipperton fracture zones of the Pacific.In France, CNEXO (Centre National pour L'Exploitation des Oceans) and its research group, AFERNOD (Association Francais d'Étude et de Recherche des Nodules océaniques) are carrying out “Rsearches on polymetallic (manganese) nodules”, mostly for the southern Central Pacific Basin.In England, a research group has done recently some research cruises on the manganese nodules and metalliferous sediments for the Indian Ocean.

著者

神保 小虎

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.1, no.4, pp.165-168, 1889-04-25 (Released:2010-10-13)

著者

渡邊 久吉

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.25, no.11, pp.784-786, 1913-11-15 (Released:2010-10-13)

著者

小泉 武栄

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.98, no.1, pp.73-81, 1989-02-25 (Released:2009-11-12)

参考文献数

7

著者

菊地 俊夫

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.120, no.2, pp.433-434, 2011-04-25 (Released:2011-06-30)

著者

斎藤 実篤

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.100, no.4, pp.616-627, 1991-08-25 (Released:2010-11-18)

参考文献数

45

被引用文献数

1

---

Structural characteristics of Recent forearc regions can be divided into three types (shelf type, terrace type, slope type) in terms of the morphology of forearc basins and the topography of basements. The differences in forearc structure seems to correspond with the difference in deformation style of forearc lithospher by subduction. Supply and/or subduction of sediments at trench are secondary factor of forearc deformation. High plate convergence rate leads to widely uplifting of island arc less subsidence of forearc basin (shelf type). Conversely, low plate convergence rate leads to one-sided subsidence of trench side and increasing in undulation of forearc topography (slope type).Sediments from forearc basin can reconstruct the subsidence rate of forearc basin and the vertical movement of island arc and by use of planktonic microfossils and benthic for eminifera which determine the changes in sedimentation rate and paleobathymetry. Thus, forearc basins are tectonic recorder to estimete the arc evolution and the change in subduction styles.

著者

安田 喜憲

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.94, no.7, pp.586-594, 1986-01-25 (Released:2009-11-12)

参考文献数

59

被引用文献数

1 1

著者

小池 拓矢 菊地 俊夫

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.125, no.6, pp.857-870, 2016-12-25 (Released:2017-01-25)

参考文献数

27

被引用文献数

2 6

---

The objective of this study is to clarify how the landscape is evaluated by participants of geo-tours on Izu-Oshima Island. The Visitor-employed photography (VEP) method is used to identify places where landscape evaluations are concentrated and objects are photographed frequently. Further, this study discusses the impact of interpretations by tour guides on the landscape evaluations of participants. Izu-Oshima Island, located 120 km south of Tokyo, is a volcanic island which was certified as a geopark in 2010. In this study, university students, who were part of a field excursion, were divided into two groups and accompanied by two tour guides. The results of a Kernel density estimation shows that the locations of photographs taken by the tour participants are concentrated in areas where the tour guides provide interpretations. These locations differ by tour group, which indicates that landscape evaluations are influenced interpretations. Each participant chose five favorite photographs from among their own photographs. Photographs of people were preferred. Tour participants took photographs of geological and geographical features as records; however, photographs of people were preferred as happy memories with friends during the tour. It is important to have both academic and entertaining contents in interpretations during educational activities of Geoparks.

著者

戎崎 俊一

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.127, no.5, pp.577-607, 2018-10-25 (Released:2018-11-14)

参考文献数

122

被引用文献数

2 3

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“Tandem” planet formation, a new theory of planet formation, is described. A steady-state, 1-D model of the accretion disk of a protostar is obtained taking into account magneto-rotational instability (MRI) and porous aggregation of solid particles. The disk is found to be divided into an outer turbulent region, a MRI suppressed region, and an inner turbulent region. The outer turbulent region is fully turbulent because of MRI. However, MRI is suppressed around the midplane of the gas disk, and a quiet area without turbulence appears at rout ( 8-60 AU) from the central star, because the degree of ionization of gas becomes sufficiently low. The disk becomes fully turbulent again at rin ( 0.2-1 AU), because the midplane temperature becomes sufficiently high (> 1000 K). Planetesimals are formed through gravitational instability at both outer and inner MRI fronts. At the outer MRI front, icy particles grow through low-velocity collisions into porous aggregates with low densities (down to ≃ 105 g cm−3). They eventually undergo gravitational instability to form icy planetesimals. Rocky particles, on the other hand, accumulate at the inner MRI front due to the local maximum in gas pressure. They undergo gravitational instability in a sub-disk of pebbles to form rocky planetesimals. They are likely to be volatile-free because of the high temperature (> 1000 K) at this formation site. This is consistent with a model in which the Earth was initially formed as a completely volatile-free planet. Water and other volatile elements came later through the accretion of icy particles with occasional scatterings in the outer regions after solidification of the planet surface. Our new proposed tandem planet formation regime shows that planetesimals are formed at two distinct sites. The former is likely to be the source of outer gas giants and the latter of inner rocky planets. The tandem regime also explains the gap in the distribution of solid components (2-4 AU), and therefore a relatively small Mars and a very small mass in the main asteroid belt. This tandem regime is found not to take place when the vertical magnetic field of the disk is five times weaker than that assumed, because the outer MRI front shifts outward beyond 100 AU. Such a “dispersed planetary formation” regime may explain high eccentricity planets, which are detected in exosolar planetary systems. On the other hand, when the ionization rate due to galactic cosmic-rays is 100 times larger than that of the present value, the outer MRI front shifts down to the inside of the water sublimation zone. Such a “single star formation” regime might explain super Earths or hot Jupiters, because almost all of the rock components in the disk transported to the inner MRI front contribute to planetary formation.

著者

鈴木 康弘 渡辺 満久 廣内 大助

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.113, no.6, pp.861-870, 2004-12-25 (Released:2009-11-12)

参考文献数

9

被引用文献数

8 9

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The surface faults of the Mid Niigata prefecture Earthquake in 2004 appeared along preexisting active fault traces (lines) of the Obirou fault, as well as the northern part of the western marginal fault of the Muikamachi basin. The vertical displacement of surface faults are within 30 cm, and the three areas with distinct faults can be summarized as follows. At Obirou, in Hirokami village (Uonuma city), the road surface is vertically displaced by approximately 30 cm just along the active fault line, and the waterways located on the fault line are compressed and broken. At Shitakura, in the Horinouchi town (Uonuma city), the surfaces of both the highway and the old road are cracked and vertically displaced by approximately 20 cm. At Aoshima, in Koide town (Uonuma city), the surface faults clearly extend over 500 m in length. Paddy fields, gardens, waterways, roads, and houses are vertically displaced by approximately 20 cm. The facts mentioned above indicate that the Mid Niigata prefecture Earthquake in 2004 (probably the main shock) was caused by the rejuvenation of these active faults.

著者

吉井 敏尅

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.94, no.7, pp.648-655, 1986-01-25 (Released:2009-11-12)

参考文献数

8

著者

平内 健一 片山 郁夫

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.124, no.3, pp.371-396, 2015-06-25 (Released:2015-07-10)

参考文献数

140

被引用文献数

3 5

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Serpentine minerals (lizardite, chrysotile, and antigorite) are a major group of hydrous phyllosilicates resulting from the hydrothermal alteration of mantle peridotite. Their distinct rheological properties mean that serpentine minerals have a strong influence on the mechanical and seismogenic behavior of faults and plate boundaries in both continental and oceanic settings. In this paper we review the results of laboratory experiments performed to understand the frictional and mechanical properties, and deformation mechanisms of serpentinite. Frictional sliding experiments at low slip rates show that antigorite exhibits velocity-strengthening behavior (a−b > 0) over a wide range of temperature (25-400°C) , while values of (a−b) for chrysotile become negative as temperature increases (25-281°C) . This indicates that the stability of slip along serpentinite-bearing faults depends on the serpentine species and fault depth. Frictional sliding of antigorite at seismic slip rates leads to weakening by flash heating. Axial compression experiments at confining pressures of up to 4 GPa show that antigorite is stronger than lizardite by at least a factor of two. The flow law for dislocation creep of antigorite based on stress values at 〜15% strain also predicts differential stresses that are substantially lower than those for the dislocation creep of olivine at natural strain rates (10−10 to 10−14 s−1) . This suggests that the viscosity of serpentinite promotes slab–mantle decoupling. However, the antigorite flow law should be used with caution because antigorite starts to deform by semi-brittle flow after 〜20% strain. Large-strain simple-shear deformation of antigorite aggregates at high pressure (1 GPa) results in a strong alignment of antigorite c-axes normal to the shear plane. This observation explains the trench-parallel anisotropy beneath the Ryukyu subduction zone. Although dehydration embrittlement is considered a primary cause of intermediate-depth earthquakes, recent high-pressure experiments on antigorite show stable sliding behavior or detect no acoustic emissions during dehydration reactions. We emphasize that the presence of talc derived from the metasomatic alteration of serpentine further weakens and stabilizes the slab–mantle interface and promotes long-lived ( > 1 Ma) detachment faulting.

著者

石村 満宏

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.94, no.4, pp.256-265, 1985-08-25 (Released:2010-10-13)

参考文献数

16

被引用文献数

1