1.

論文(リポジトリ)

論文(リポジトリ)
Matrika Prasad, Koirala ; Hayashi, Daigoro ; 林, 大五郎
出版情報: 琉球大学理学部紀要 = Bulletin of the College of Science. University of the Ryukyus.  pp.7-16,  2011-09.  琉球大学理学部
URL: http://hdl.handle.net/20.500.12000/22087
概要: Many interesting findings were obtained during the INDEPTH geophysical surveys but the results of these surveys were not sufficient to explore the deep crustal relations among the Himalayan Mega Thrust namely MCT, STD and GCT. In this study, 2-D finite element method was used to analyze the state of stress and deep crustal relation between MCT, STD and GCT. Elasto-plastic, plane strain model constrained by the northward convergent displacement boundary condition was used to simulate the stress field. Modelling results reveal that thrust/fault geometry, their deep crustal relations and how do they terminate had effect on the stress field, displacement vector, shear stress and exhumation. The lateral variation of the stress orientation and surface exposure of fault/thrust and lithologic units may be the expression of the deep crustal relations between the major structures, their geometry and how do they terminate at the depth. So the along strike variation in the Himalaya may be the manifestation of structural geometry and their deep crustal relationships. 続きを見る
2.

論文(リポジトリ)

論文(リポジトリ)
Dwivedi, Sunil Kumar ; Hayashi, Daigoro ; 林, 大五郎
出版情報: 琉球大学理学部紀要 = Bulletin of the College of Science. University of the Ryukyus.  pp.5-25,  2010-03.  琉球大学理学部
URL: http://hdl.handle.net/20.500.12000/17387
概要: The present-day stress field in the Earth's crust is important and provides insights into mechanisms that drive pla te motions. In this study, an elastic plane stress finite element modeling incorporating realistic rock parameters have been used to calculate the stress field, displacement field and deformation of the plate interactions in Anatolia. Modeled stress data for the African-Arabian-Anatolian plate interactions with fixed Eurasian platform correlate well with observed stress indicator from the world stress map (WSM) and focal mechanism of earthquakes; while displacement field agree qualitatively well with GPS vectors and sense of motion indicated by focal mechanisms for large crustal earthquakes (M>6) and plate motion models. Modeling result shows the direction of maximum horizontal compressive stress (σ_<Hmax>) toward the direction of absolute motion of these plates. Large perturbations in σ_<Hmax> orientations are shown to occur in and around tectonic boundaries between those plates. It is observed that, although the African plate acts mostly as indenter, which transmits the collisional motion from the Arabian plate to the Anatolian plate, in the current situation the far-field stress probably from the Hellenic subduction is needed to satisfy the present-day stress field in Anatolia. 続きを見る
3.

論文(リポジトリ)

論文(リポジトリ)
Islam, Md. Shofiquul ; Hayashi, Daigoro ; 林, 大五郎
出版情報: 琉球大学理学部紀要 = Bulletin of the College of Science. University of the Ryukyus.  pp.27-58,  2010-03.  琉球大学理学部
URL: http://hdl.handle.net/20.500.12000/17407
概要: The Shillong Plateau, NE India is reported to be one of the most seismically active ‘pop-up’ structures lyin g between the Dauki fault and recently reported Oldham fault in northeast India. Dauki fault lies down faulted Bengal basin to the south and Oldham fault, the Assam valley, the Himalayan foothills region, lesser Himalaya and Butan and Tibet further north. We examined convergent displacement due to northward movement of the Indian plate with respect to the Eurasian plate and also consider uplift of the Plateau simultaneously. Four models with different boundary conditions under both plane strain and plane stress have been selected. The maximum compressive stress shows a preferred orientation that helps us to explain the tectonic environment as well as the fault pattern in plane strain condition. The realistic regional maximum horizontal compressive stress (σ_Hmax) orientation is observed within the best-fit model under plane stress condition. The best-fit model result under plane strain condition shows that the compressive stress regime is dominant in the study area, except for the uppermost part of the crust where the tensional stress is dominant. These tensional stress regimes support normal faulting and structural discontinuities. With increase progressive convergent displacement (under plane strain condition), the principal stresses rotate anticlockwise around the fault zones, and the upper crust of the Bengal basin and the Assam valley, on the other hand, behave thrust faulting. Rock properties (density, Poisson's ratio, Young's modulus, cohesion, angle of internal friction) and Mohr-Coulomb failure criterion are used to calculate failure and faulting pattern. The simulated results have significant explanation on the proposed Oldham fault as well as on the geologically evidenced Dauki fault. Our preferred model explains deformation and seismic activity of the area. Our plane stress simulation results show that the Dauki fault is the major controlling element for overall distribution of regional stress, and it accommodates ~25% horizontal displacement. Our plane strain model further suggests that plate convergence is the driving force for pop-up tectonics of the Shillong Plateau, and also for deformation in the Shillong Plateau and adjoining area within the crust (<30 km). 続きを見る
4.

論文(リポジトリ)

論文(リポジトリ)
Hayashi, Daigoro ; 林, 大五郎
出版情報: 琉球大学理学部紀要 = Bulletin of the College of Science. University of the Ryukyus.  pp.9-13,  2009-09.  琉球大学理学部
URL: http://hdl.handle.net/20.500.12000/13347
概要: 2D elastoplastic FE program has been developed in 2002 (Hayashi, 2002). Improved FE program was applied to the Umaoi hills in Hokkaido, Japan to estimate plate convergence rate (Morishita and Hayashi, 2005; Hayashi and Morishita, 2006). This FE elastoplastic software is derived from 2D von Mises' plastic theory. The detail of elastoplastic theory and FE formulation are explained in this paper. 続きを見る
5.

論文(リポジトリ)

論文(リポジトリ)
Koirala, Matrika Prasad ; Hayashi, Daigoro ; 林, 大五郎
出版情報: 琉球大学理学部紀要 = Bulletin of the College of Science. University of the Ryukyus.  pp.15-26,  2009-09.  琉球大学理学部
URL: http://hdl.handle.net/20.500.12000/13367
概要: This paper describes about field study as well as laboratory test performed for the geotechnical properties of rock and soil along the Tinpiple-Banchare Dada road alignment. The purpose of the present study was to determine the geotechnical properties for both rocks and soils along the road alignment. Detailed geotechnical soil/rock field study sheets were used to record geotechnical parameters in the field and to know the site condition. Dynamic cone penetration test was performed in the in situ soil. Laboratory test were performed for the classification of the soil, and to determine the optimum moisture content. Results reveal that most part of the road is aligned through the completely weathered sandstone, its residual soil (classified as SM) along with the gneisses. The results of the Dynamic Cone Penetration Test show that minimum CBR % varies from 18% at 10 cm depth to 2% at 58 cm. These values of the CBR % are considered good so no capping is required. The results of the compaction test show that maximum dry density for most of the samples were obtained at 10-15 % optimum moisture content. The results of the joint analysis revealed that chainage 2+ 115, 2+475, 5+125 to 5+ 175 and 7+220 km has probability of lateral, lateral / central, central and central wedge failure respectively. Small landslides were initiated in upslope side due to road cutting and can be stabilized by simple bioengineering techniques. The results of this study are very important for the construction of a sound road and should be considered during the full phase onstruction of the road. 続きを見る
6.

論文(リポジトリ)

論文(リポジトリ)
Suzuki, Ryota ; Hayashi, Daigoro ; 林, 大五郎
出版情報: 琉球大学理学部紀要 = Bulletin of the College of Science. University of the Ryukyus.  pp.47-68,  2009-03.  琉球大学理学部
URL: http://hdl.handle.net/20.500.12000/9530
概要: Finite element (FE) modeling has designed to investigate dynamics of Southern Ryukyu Arc based on synthesized stress-strain, velocity, geology and seismicity data. Result of horizontal minimum stress (σHmin) orientation is compared to present stress distribution. We constructed 1300 km X 600 km model for Southern Ryukyu Arc. FE model was bounded along the Ryukyu Trench. Studied region is divided into 3 domains: arc region, Okinawa Trough and continental margin. As displacement velocity is 9.0 cm/yr in Taiwan, we set up NW boundary displacement of 2000 m that correspond to c.a. 20,000 year on Ryukyu Trench to Taiwan. Four boundary conditions under 1, 10 and 30 km depth are considered. In addition, single domain model is also constructed. Total 16 experiments are performed. Result of σHmin orientation shows good agreement with T-axis distribution in Taiwan and Ryukyu Arc (Kubo and Fukuyama, 2003; Otsubo and Hayashi, 2003). In addition, large stress concentrates on eastern area of Taiwan while in Okinawa trough, computed σHmin orientation is arc-parallel which is inconsistent with observed σHmin orientation. Depth affects greatly to the stress magnitude but not to stress orientations in the Ryukyu Arc. It is found that orientation of σHmin is principally controlled by rock domain properties of major structural zones and the direction of convergence of the Philippine Sea plate relative to Eurasia. Direction of displacement vector is good agreement with that of observed velocity field in Taiwan, while direction of displacement vector is trending NW or W in Okinawa trough and Ryukyu Arc, indicating that this model does not fit in this point. 続きを見る
7.

論文(リポジトリ)

論文(リポジトリ)
Joshi, Ganesh Raj ; Hayashi, Daigoro ; 林, 大五郎
出版情報: 琉球大学理学部紀要 = Bulletin of the College of Science. University of the Ryukyus.  pp.1-37,  2008-03.  琉球大学理学部
URL: http://hdl.handle.net/20.500.12000/5608
概要: The immense Himalayan arc is evolved as a consequence of the collision between Indian and Eurasian landmasses some 50 million year ago. The Indian plate converges northward at the average rate of 20.5 ± 2 mm/year (Bilham et al., 1988), and is under-thrusting beneath Tibet. This continuous northward penetration of India under Eurasia has produced the broad zone of active crustal deformation, shortening, slicing and surface uplift of the northern margin of the Indian continent; and build up the Himalaya is under very strong compressive strain that made the entire Himalayan region one of the most seismotectonically dynamic intercontinental regions of the world. In the present study, an approach has been made to model a NE-SW cross-section (Ram et al., 2005) extending from the Gangetic Plain to the Tethys Himalaya including potentially active major faults by means of FE method (Hayashi, 2008) considering an elastic rheology under plane strain condition with convergent boundary environment in the fold-and-thrust belt of the Garhwal Himalaya. The present study provides an opportunity to understand the neotectonic stress distribution, style of deformation and present day shortening rate in the Himalayan front. Simulation results reveal that the compressive stress of stress developed in the northern part and tensional stress fields developed in the southern part of the Garhwal Himalaya, and consequently, thrust are developed in the north and normal faults are developed in southern regions respectively, which is consistent with the characteristics of the fold and thrust belt. Furthermore, modeling results show good agreement with the Quaternary deformation, active faulting, microseismicity and focal mechanism solution of the fold-and-thrust belt of the Garhwal Himalaya. 続きを見る
8.

論文(リポジトリ)

論文(リポジトリ)
Chamlagain, Deepak ; Hayashi, Daigoro ; 林, 大五郎
出版情報: 琉球大学理学部紀要 = Bulletin of the College of Science. University of the Ryukyus.  pp.39-79,  2008-03.  琉球大学理学部
URL: http://hdl.handle.net/20.500.12000/5609
概要: An understanding of orientation of contemporary maximum horizontal compressive stress (σ_<Hmax>) is important to many aspects of earth sciences, e.g. seismicity, neotectonics, and plate driving mechanisms. Comparison of recent stress observations and the results of stress modeling provide a powerful approach to refine our understanding of geodynamics processes. This is especially important for complex area like Himalayan-Tibet orogen, a continental collision zone between the Indian and Eurasian Plates. The frequently occurring earthquakes and other tectonic stress indicator have provided vast set of database on maximum horizontal compressive stress (σ_<Hmax>) that can be useful to study contemporary stress sources, plate kinematics and ongoing geodynamics. In this contribution, taking advantage of elastic plane stress finite element modeling (FEM), and observed data on σ_<Hmax>, several models are presented to reproduce stress field. Simulated models show that the convergence normal to the orogen is essential to reproduce observed σ_<Hmax>, which in turn controls the magnitude and orientation of σ_<Hmax>. The kinematics equivalent to east-west tectonic escape did not reproduce the observed stress field. Therefore, the best-fit model of present day stress field is obtained only in three domains model with southeastward tectonic escape of the Tibetan crust rather than eastward extrusion. There is, however, significant increase in σ_<Hmax> magnitude with increasing crustal depth because of stress amplification. Incorporation of suture zones in the model did not change orientation of σ_<Hmax>, significantly. Considering these facts, 'continuum tectonic model' is more preferable than the 'block tectonic model' for the active deformation of the Tibetan Plateau. Contemporary stress field deduced from several tectonic stress markers reconciles with the predicted one giving insights on their sources and ongoing plate kinematics of the continental collision zone between Indian and Eurasian Plates. 続きを見る
9.

論文(リポジトリ)

論文(リポジトリ)
Hayashi, Daigoro ; 林, 大五郎
出版情報: 琉球大学理学部紀要 = Bulletin of the College of Science. University of the Ryukyus.  pp.81-95,  2008-03.  琉球大学理学部
URL: http://hdl.handle.net/20.500.12000/5610
概要: Theoretical basis of a FE software package is explained in term of the theory of finite element method, 2D elastic FE problem, fault analysis, physical property of rocks. Flow chart and function of the FE software package is added to see the perspective view among many programs. The aim of the paper is to show the soundness of the FE software package which is used in the Simulation Tectonic Laboratory. 続きを見る
10.

論文(リポジトリ)

論文(リポジトリ)
Hayashi, Daigoro ; 林, 大五郎
出版情報: 琉球大学理学部紀要 = Bulletin of the College of Science. University of the Ryukyus.  pp.5-17,  2008-10.  琉球大学理学部
URL: http://hdl.handle.net/20.500.12000/7648
概要: The Main Central Thrust (MCT) zone is one of the most important tectonic zones of the Himalayas along which the inverted metamorphism has been observed. The MCT zone around Annapurna have been surveyed to analyse 3D strain by adopting the least square method (Hayashi, 1994,2001). The problem which is encountered in treating 3D strain analysis, is the precision of strain. The consistent value (c-value) was derived to estimate how the resultant value of strain is consistent with true value (Hayashi, 1995). Setting the c-value properly, invalid samples are excluded from the strain analysis. The paper summarized as its important result that the foliation plane and XY plane are almost parallel together. Although this result has been recognized as a general agreement by many geologists, there has been no direct proof using 3D strain analysis up to now. Shear heating model is considered as the reasonable cause of inverted metamorphism along the MCT from the intermediate intensity of strain. The 3D strain analysis introduced here has benefits that any rock which is composed of grains can be used as marker rock and we can find out such rocks ubiquitously throughout the Himalayas. 続きを見る