Outflow channel sources, reactivation, and chaos formation, Xanthe Terra, Mars     

Jose A.P. Rodriguez  Sho Sasaki  James M. Dohm  Hideaki Miyamoto  Goro Komatsu  Justin C. Ferris 《Icarus》2005,175(1):36-57

The undulating, warped, and densely fractured surfaces of highland regions east of Valles Marineris (located north of the eastern Aureum Chaos, east of the Hydraotes Chaos, and south of the Hydaspis Chaos) resulted from extensional surface warping related to ground subsidence, caused when pressurized water confined in subterranean caverns was released to the surface. Water emanations formed crater lakes and resulted in channeling episodes involved in the excavation of Ares, Tiu, and Simud Valles of the eastern part of the circum-Chryse outflow channel system. Progressive surface subsidence and associated reduction of the subsurface cavernous volume, and/or episodes of magmatic-driven activity, led to increases of the hydrostatic pressure, resulting in reactivation of both catastrophic and non-catastrophic outflow activity. Ancient cratered highland and basin materials that underwent large-scale subsidence grade into densely fractured terrains. Collapse of rock materials in these regions resulted in the formation of chaotic terrains, which occur in and near the headwaters of the eastern circum-Chryse outflow channels. The deepest chaotic terrain in the Hydaspis Chaos region resulted from the collapse of pre-existing outflow channel floors. The release of volatiles and related collapse may have included water emanations not necessarily linked to catastrophic outflow. Basal warming related to dike intrusions, thermokarst activity involving wet sediments and/or dissected ice-enriched country rock, permafrost exposed to the atmosphere by extensional tectonism and channel incision, and/or the injection of water into porous floor material, may have enhanced outflow channel floor instability and subsequent collapse. In addition to the possible genetic linkage to outflow channel development dating back to at least the Late Noachian, clear disruption of impact craters with pristine ejecta blankets and rims, as well as preservation of fine tectonic fabrics, suggest that plateau subsidence and chaos formation may have continued well into the Amazonian Period. The geologic and paleohydrologic histories presented here have important implications, as new mechanisms for outflow channel formation and other fluvial activity are described, and new reactivation mechanisms are proposed for the origin of chaotic terrain as contributors to flooding. Detailed geomorphic analysis indicates that subterranean caverns may have been exposed during chaos formation, and thus chaotic terrains mark prime locations for future geologic, hydrologic, and possible astrobiologic exploration.  相似文献   

A geological interpretation of the lunar surface     

S. Miyamoto 《Planetary and Space Science》1960,2(4):256-260

This interpretation of lunar surface features is based on the differentiation of siliceous and basaltic substances similar to those of the earth. Our hypothesis is that lunar maria are composed of basaltic matter similar to that of terrestrial ocean basins, and that the lunar continents (bright regions) are composed of siliceous blocks.  相似文献   

Turbulent structure in water under laboratory wind waves     

Ikuo Yoshikawa  Hiroshi Kawamura  Kuniaki Okuda  Yoshiaki Toba 《Journal of Oceanography》1988,44(3):143-156

The structure of the turbulent boundary layer underneath laboratory wind waves was studied by using a combination of a high-sensitivity thermometer array with a two-component sonic flowmeter. The temperature fluctuations are used to detect movements of water parcels, with temperature as a passive quantity. The turbulence energy was dominant in the frequency range (0.01 0.1 Hz), which was much smaller than the wind-wave frequency (2 5 Hz), and in which the turbulence was anisotropic. There was a frequency range (0.2 2 Hz for velocity, 0.2 5 Hz for temperature fluctuation) where the turbulence was isotropic and had a –5/3 slope in the energy spectrum. These points are the same as those in previous works. However, by analyses of the time series by using a variable-interval time-averaging technique (VITA), it has been found that conspicuous events in this main turbulence energy band are the downward bursting from the vicinity of the water surface. Thus the structure of the water layer underneath the wind waves has characters which are similar to the familiar turbulent boundary layer over a rough solid wall, as already conceived. It has been found that, at the same time, the turbulence energy can be related to quantities of the wind waves (the root mean squared water level fluctuation and the wave peak frequency), for different wind and wave conditions. That is, the turbulence underneath the wind waves develops under a close coupling with the wind waves.  相似文献   

Branching and joining of the Tsushima Current around the Oki Islands     

Osamu Katoh  Kenji Morinaga  Kuniaki Miyaji  Kazuyuki Teshima 《Journal of Oceanography》1996,52(6):747-761

We discussed the branching and joining of the Tsushima Current around the Oki Islands, based on ADCP and CTD measurements carried out in June 1990 by the quadrireciprocal method (Katoh, 1988). The volume transport of the northeastward current northwest of the Izumo Coast was about 2 Sv. The triple-branch structure of the Tsushima Current was obscure there. This northeastward current divided into the eastward and northward currents, with volume transports of 0.5 Sv and 1.5 Sv, respectively, at the west entrance of the Oki Strait. Most of the first branch of the Tsushima Current seemed to be separated again from the other confluent branches and to pass through the Oki Strait as this eastward current. The northward current was composed of the second and the third branches of the Tsushima Current. It detoured the Oki Islands, and almost all of it returned south to the Tajima Coast. In the vicinity of the Tajima Coast, the eastward current was abruptly strengthened through the confluence of the southward one which was originated from the northward current west of the Oki Islands. This showed that the first branch finally joined the compound of the second and the third branches detouring the Oki Islands. Between the Oki Strait and the Tajima Coast, the two-layer structure of currents was clearly found.  相似文献   

Structure of Subsurface Intrusion of the Oyashio Water into the Kuroshio Extension and Formation Process of the North Pacific Intermediate Water     

Kuniaki Okuda  Ichiro Yasuda  Yutaka Hiroe  Yugo Shimizu 《Journal of Oceanography》2001,57(2):121-140

In order to understand the actual formation process of the North Pacific Intermediate Water (NPIW), structure of subsurface intrusions of the Oyashio water and the mixing of the Oyashio and the Kuroshio waters in and around the Kuroshio Extension (KE) were examined on the basis of a synoptic CTD observation carried out in May-June 1992. The fresh Oyashio water in the south of Hokkaido was transported into KE region through the Mixed Water Region (MWR) in the form of subsurface intrusions along two main paths. The one was along the east coast of northern Japan through the First Branch of the Oyashio (FBO) and the other along the eastern face of a warm streamer which connected KE with a warm core ring through the Second Branch of the Oyashio (SBO). The fresh Oyashio water extended southward through FBO strongly mixed with the saline NPIW transported by the Kuroshio in the south of Japan (old NPIW) in and around the warm streamer. On the other hand, the one through SBO well preserved its original properties and extended eastward beyond 150°E along KE with a form of rather narrow band. The intrusion ejected Oyashio water lens with a diameter of 50–60 km southward across KE axis and split northward into the MWR involved in the interaction of KE and a warm core ring, which were supposed to be primary processes of new NPIW formation.  相似文献   

Structure of X-ray irradiated stellar wind     

Kuniaki Masai 《Astrophysics and Space Science》1984,106(2):391-407

The effect of X-ray irradiation on the line-driven stellar wind in X-ray binary systems is studied. The product of the X-ray luminosityL _x and the densityn in the wind is a measure to distinguish between the optically thin and thick wind regimes. For an X-ray source of the radiation temperature of 10 keV, the critical value(L _x n) _c , is of the order of 10³⁷ erg s^–1 cm^–3; hence, most of wind-fed X-ray sources lie in the optically thick wind regime because ofL _x n>(L _x n) _c . Then the wind structure is determined not only by the parameter =(L _x /nR ²),R the distance from the X-ray source, but also by the optical thickness due to helium. The formation of fully ionized helium region depends onL _x andn in a way different from that of the Strömgren sphere. In such an optically thick wind, the region behind the He II ionization boundary is little affected by X-ray irradiation and the trace elements remain to be responsible for wind acceleration. Thus, its location is important for the structure of the wind and the interpretation of various phenomena in objects such as wind-fed X-ray pulsars.  相似文献   

Limit states and failure mechanisms of viscous dampers and the implications for large earthquakes     

H. Kit Miyamoto  Amir S. J. Gilani  Akira Wada  Christopher Ariyaratana 《地震工程与结构动力学》2010,39(11):1279-1297

Fluid viscous dampers are used to control story drifts and member forces in structures during earthquake events. These elements provide satisfactory performance at the design‐level or maximum considered earthquake. However, buildings using fluid viscous dampers have not been subjected to very large earthquakes with intensities greater than the design and maximum considered events. Furthermore, an extensive database of viscous damper performance during large seismic events does not exist. To address these issues, a comprehensive analytical and experimental investigation was conducted to determine the performance of damped structures subjected to large earthquakes. A critical component of this research was the development and verification of a detailed viscous damper mathematical model that incorporates limit states. The development of this model and the laboratory and simulation results conclude good correlation with the new model and the damper limit states and provide superior results compared with the typical damper model when considering near collapse evaluation of structures. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Heat capacity,compressibility and thermal expansion coefficient of ilmenite-type MgGeO3     

T. Ashida  Y. Miyamoto  S. Kume 《Physics and Chemistry of Minerals》1985,12(3):129-131

The accuracy of differential scanning calorimetry (DSC) on a heat capacity measurement was evaluated using MgO. The result indicated that the deviation of the result in comparison to literature values was less than 0.4% at temperatures above 300 K and 2.1% below this temperature. Since this experiment proved the reliability of DSC, heat capacity, compressibility, and thermal expansion of ilmenite-type MgGeO₃ were measured by means of DSC, a diamond anvil high pressure device, and a high-temperature X-ray camera, respectively. The heat capacity was approximated by C _p = a + b·T + c·T ^?2 at high temperatures and by the Debye function at low temperatures. The compressibility was well-represented by the Murnaghan-Birch equation of 2nd order. The thermal expansion coefficient was constant up to 1073 K.  相似文献   

Phases Representing Source Lengths of Tsunami in Tide Gauge Records     

Kuniaki Abe 《Pure and Applied Geophysics》2007,164(2-3):453-463

We identified a phase representing the source length of tsunami's in the tide gauge records around Japan. This phase was observed at tide stations, located in the direction of the long axis of the sources, for four large tsunamis: 1964 Niigata, 1968 Tokachi-oki, 1983 Nihonkaichubu, and 1993 Hokkaido-nanseioki. The phase consists of two continuous crests starting as the initial arrival and has a time length of 15–47 minutes. This is the time required to propagate across the source area along the long axis. Strong evidence that the phase is generated at the source is the good correlation between waveform observed at one side and time-inversed waveform at another side. The correlation results from the instantaneous generation of the source. The source lengths of 74–254 km were obtained under an assumption of sea depths at the sources and verified to coincide with ones within a relative error of 15% that were previously obtained by other methods.  相似文献   

Changes in major element hydrochemistry of the Pecos River in the American Southwest since 1935     

Fasong Yuan  Seiichi Miyamoto  Shilpa Anand 《Applied Geochemistry》2007

The Pecos River, situated in eastern New Mexico and western Texas, receives water from a drainage area of 91 000 km². There are primarily two major water inputs, namely snowmelt from winter storms in the headwater region of the southern Rocky Mountains and runoff from warm-season monsoonal rainfall in the lower valley. The Pecos River suffers from high levels of total dissolved solids (TDS >5000 mg L⁻¹) under normal flow conditions. This not only poses serious problems for agricultural irrigation and safe drinking water supply, but also results in a permanent loss of biodiversity. This study examines changes in stream flow and water chemistry of the Pecos River over the last 70 a to better understand the long-term variability in stream salinity and the role of agricultural practices in salt transfer. A TDS record from the lower Pecos River near Langtry (Texas) back to 1935 was extracted to show a distinct pattern of decadal variability similar to the Pacific Decadal Oscillation (PDO), in which stream salinity is overall above average when the PDO is in positive (warm) phase and below average when the PDO is in negative (cold) phase. This is due to: (1) the dissolved salts contributed to the river are largely from dissolution of NaCl and CaSO₄-bearing minerals (e.g., halite and gypsum) in the upper basin, (2) the amount of the dissolved salts that reach the lower basin is mainly determined by the stream flow yield in the upper basin and (3) the stream flow yield from the upper basin is positively correlated with the PDO index. This further attests that large-scale climatic oscillation is the major source of long-term changes in stream flow and salinity of the Pecos River. On the other hand, there is also a strong indication that the rate of salt export has been affected by reservoir operations and water diversions for agricultural practices.  相似文献