Application of a Simulation Model for the Formation of Methane Hydrate to the Nankai Trough and the Blake Ridge: Natural Examples of Two End-member Cases     

Kei Baba  Arata Katoh 《Resource Geology》2004,54(1):125-135

Abstract. Simulation experiments with a one-dimensional static model for formation of methane hydrate are used to demonstrate models of hydrate occurrence and its generation mechanism for two end-member cases. The simulation results compare well with experimental data for two natural examples (the Nankai Trough and the Blake Ridge).
At the MITI Nankai Trough wells, the hydrate occurrence is characterized by strongly hydrated sediments developing just above the BGHS. Such occurrence can be reproduced well by simulation in which the end-member case of upward advective fluid flow from below the BGHS is set. The strongly hydrated sediments is formed by oversaturated solution with free gas which directly enters the BGHS by the upward advective fluid flow. The recycling of dissociated methane of preexisting hydrate also contributes to the increase of hydrate saturation.
At the Site 997 in the Blake Ridge area, the hydrate occurrence is characterized by thick zone with poorly hydrated sediments and no hydrate zone developing above the hydrate zone. Such occurrence can be reproduced well by simulation in which the end-member case of in-situ biogenic production of methane in the sediment of methane hydrate zone is set. The distribution pattern of hydrate saturation is basically controlled by that of TOC. However, the hydrate concentration near the bottom of the hydrate zone is increased by the effect of recycling of dissociated methane of pre-existing hydrate. No hydrate zone expresses the geologic time needed until the local concentration of methane exceeds the solubility by gradual accumulation of in-situ biogenic methane with burial.  相似文献   

Computation of wave transmission over a shore protecting submerged breakwater     

M Baba 《Ocean Engineering》1986,13(3)

Among the offshore breakwaters which are increasingly used in shore protection projects, a bevelled block submerged breakwater with 1 on 1.67 seaward slope and a vertical shoreward face is most advantageous, especially from the point of view of optimum wave damping, minimum wave reflection and maximum sand trapping effects. Different computational methods of wave transmission coefficient of this breakwater are examined with laboratory tests. The Goda's method is found to be the simplest and most suitable in the case of the shore protecting submerged breakwater. However, the consideration of wave steepness also, in selecting the constants may yield better results with this method.  相似文献   

Analysis of the Tsunami of December 26, 2004, on the Kerala Coast of India—Part I: Amplitudes     

N. P. Kurian  M. Baba  K. Rajith  N. Nirupama  T. S. Murty 《Marine Geodesy》2006,29(4):265-270

The Indian Ocean tsunami of December 26, 2004, not only affected the Bay of Bengal coast of India but also part of the Arabian Sea coast of India. In particular, the tsunami caused loss of life and heavy damage on some parts of the Kerala coast in southwest India. The tsunami traveled west, south of Sri Lanka, and some of the tsunami energy was diffracted around Sri Lanka and the southern tip of India and moved northward into the Arabian Sea. However, tsunami, being a long gravity wave with a wave length of a few hundred kilometers, has to take a wide turn. In that process, it missed the very southern part of the Kerala coast and did not achieve large amplitudes there. However, further north, the tsunami achieved amplitudes of upto 5 m and caused loss of life and significant damage. Here we identify the physical oceanographic processes that were responsible for selective amplification of the tsunami in certain locations.  相似文献   

Changing trends in water sources and related pathologies in small to medium size African cities     

Baba Adamu  Humphrey Ngala Ndi 《GeoJournal》2018,83(4):885-896

Global exponential water demand has resulted in the quantity and quality of household water declining rapidly in recent years. Across Sub-Saharan Africa, many small to medium size towns growing at more than 5% per annum provide the region’s momentum for urbanisation. Owing to the dismal performances of water utilities companies, urban populations have tended to resort to diverse and unsafe sources of household water. Illustrating with the city of Buea in the coastal south west Cameroon, this paper examines the changing trends in water sources and the potential health risks to its populations. It relied on a blend of information ranging from reviews of relevant secondary sources, empirical data to field surveys and laboratory analysis. Key findings point to a high level of water misallocation and non-revenue water by the water utility company; a growing movement of households from the certified pipe-borne water source to unimproved sources as follows: 36% to springs, 20% to wells, 25% to water vendors, 27% to rainwater, and 22% to boreholes and only 11% from open streams to piped water. This has resulted in the presence of coliform bacteria in all alternative water sources in Buea, corroborated by hospital returns on water borne intestinal bacterial infections. Given the proven efficiency of water distribution via public pumps and smaller retailers, there is the urgent need for a change of the water distribution paradigm in small and medium size cities in Sub-Saharan Africa to increase access for more people than through the more costly home connections preferred by utility companies.  相似文献   

Metamorphic P-T conditions and variation of REE between two garnet generations from granulites in the Sør-Rondane mountains,East Antarctica     

Baba  Sotaro  Osanai  Yasuhito  Adachi  Tatsuro  Nakano  Nobuhiko  Hokada  Tomokazu  Toyoshima  Tsuyoshi 《Mineralogy and Petrology》2019,113(6):821-845

Mineralogy and Petrology - In this paper, we describe the metamorphic conditions of Fe-rich granulite and variations in rare earth elements (REE) between peak garnet porphyroblasts and secondary...  相似文献   

Shift-and-add reconstruction of solar granulation images     

Baba  N.  Miura  N.  Sakurai  T.  Ichimoto  K.  Soltau  D.  Brandt  P. 《Solar physics》1999,188(1):41-46

To restore an atmospherically degraded image of solar granulation the shift-and-add (SAA) method is applied to its specklegrams. It is the first time, to the best of our knowledge, that such a technique has been used for image reconstruction of solar granulation, a largely extended target. SAA, therefore, enables us to monitor restored images of solar granulation in a simple and fast way.  相似文献   

Validation and Joint Inversion of Teleseismic Waveforms for Earthquake Source Models Using Deep Ocean Bottom Pressure Records: A Case Study of the 2006 Kuril Megathrust Earthquake     

Toshitaka Baba  Phil R. Cummins  Hong Kie Thio  Hiroaki Tsushima 《Pure and Applied Geophysics》2009,166(1-2):55-76

The importance of accurate tsunami simulation has increased since the 2004 Sumatra-Andaman earthquake and the Indian Ocean tsunami that followed it, because it is an important tool for inundation mapping and, potentially, tsunami warning. An important source of uncertainty in tsunami simulations is the source model, which is often estimated from some combination of seismic, geodetic or geological data. A magnitude 8.3 earthquake that occurred in the Kuril subduction zone on 15 November, 2006 resulted in the first teletsunami to be widely recorded by bottom pressure recorders deployed in the northern Pacific Ocean. Because these recordings were unaffected by shallow complicated bathymetry near the coast, this provides a unique opportunity to investigate whether seismic rupture models can be inferred from teleseismic waves with sufficient accuracy to be used to forecast teletsunami. In this study, we estimated the rupture model of the 2006 Kuril earthquake by inverting the teleseimic waves and used that to model the tsunami source. The tsunami propagation was then calculated by solving the linear long-wave equations. We found that the simulated 2006 Kuril tsunami compared very well to the ocean bottom recordings when simultaneously using P and long-period surface waves in the earthquake source process inversion.  相似文献   

Roles of atmospheric variabilities in the formation of the Indian Ocean Dipole     

Baba  Yuya 《Ocean Dynamics》2020,70(1):21-39

Ocean Dynamics - Roles of atmospheric variabilities in the formation of Indian Ocean Dipole (IOD) were investigated using an ocean general circulation model and different atmospheric forcing...  相似文献   

Stability Behavior and Thermodynamic States of Iron and Manganese in Sandy Soil Aquifer,Manukan Island,Malaysia     

Chin Yik Lin  Mohd. Harun Abdullah  Baba Musta  Sarva Mangala Praveena  Ahmad Zaharin Aris 《Natural Resources Research》2011,20(1):45-56

A total of 20 soil samples were collected from 10 boreholes constructed in the low lying area, which included ancillary samples taken from the high elevation area. Redox processes were investigated in the soil as well as groundwater in the shallow groundwater aquifer of Manukan Island, Sabah, Malaysia. Groundwater samples (n = 10) from each boreholes were also collected in the low lying area to understand the concentrations and behaviors of Fe and Mn in the dissolved state. This study strives to obtain a general understanding of the stability behaviors on Fe and Mn at the upper unsaturated and the lower-saturated soil horizons in the low lying area of Manukan Island as these elements usually play a major role in the redox chemistry of the shallow groundwater. Thermodynamic calculations using PHREEQC showed that the groundwater samples in the study area are oversaturated with respect to goethite, hematite, Fe(OH)₃ and undersaturated with respect to manganite and pyrochroite. Low concentrations of Fe and Mn in the groundwater might be probably due to the lack of minerals of iron and manganese oxides, which exist in the sandy aquifer. In fact, high organic matters that present in the unsaturated horizon are believed to be responsible for the high Mn content in the soil. It was observed that the soil samples collected from high elevation area (BK) comprises considerable amount of Fe in both unsaturated (6675.87 mg/kg) and saturated horizons (31440.49 mg/kg) compared to the low Fe content in the low lying area. Based on the stability diagram, the groundwater composition lies within the stability field for Mn²⁺ and Fe²⁺ under suboxic condition and very close to the FeS/Fe²⁺ stability boundary. This study also shows that both pH and Eh values comprise a strong negative value thus suggesting that the redox potential is inversely dependent on the changes of pH.  相似文献   

Inferred ultrahigh-temperature metamorphism of amphibolitized olivine granulite from the Sør Rondane Mountains, East Antarctica     

Nobuhiko Nakano  Yasuhito Osanai  Sotaro Baba  Tatsuro Adachi  Tomokazu Hokada  Tsuyoshi Toyoshima 《Polar Science》2011,5(3):345-359

This paper reports the first evidence of ultrahigh-temperature (UHT) metamorphism from the Sør Rondane Mountains, eastern Dronning Maud Land, East Antarctica, which is evident as orthopyroxene + spinel symplectite in an amphibolitized mafic granulite. The granulite consists of olivine, orthopyroxene, clinopyroxene, pargasitic amphibole, plagioclase, and ilmenite, and it possesses a within-plate alkali basalt signature. The local bulk chemical composition of symplectite, major and trace element compositions, and thermodynamic calculations for the symplectite, suggest the presence of garnet at the high-pressure stage and that the symplectite formed from garnet, olivine, and primary orthopyroxene by decompression from more than 12 kbar at 1000 °C. The granulite records a subsequent amphibolite-facies overprint (<700 °C at <6 kbar) that involved the chemical re-equilibration of several phases. The obtained pressure–temperature (P–T) conditions and P–T path are different from the UHT metamorphism from the Schirmacher Hills, central Dronning Maud Land, which is considered to have occurred in a back-arc tectonic setting. The relatively high-P conditions and the decompression path reconstructed in the present study are similar to those reported for southern India, Sri Lanka, and part of northeastern Mozambique, possibly reflecting continental thickening and exhumation during the main collision event between East and West Gondwana.  相似文献