基于图像相关分析的土体剪切带识别方法

提出了一种基于数字照相量测和图像相关性分析技术的土体剪切带识别方法。首先,在模型试验中,用数码相机采集土体全程变形图像序列;接着,在图像全局观测范围内粗略搜索到剪切带发生的大致区域;然后,布置跨越剪切区域的多对测点线,进行局部范围精密搜索,识别出剪切带的准确位置与形状, 并确定剪切带的边界点。与在模型上描画网格线等传统方法相比,该法操作简单,量测准确,适用于模型试验中岩土材料的剪切带识别及其厚度、倾角、带内变形和演变过程等特性的试验研究;最后,给出了一个大型砂土剪切试验中的应用实例。结果表明,基于图像相关分析的识别土体剪切带的方法是可行而有效的。     

Photographic Observations of the 1996 Leonid Fireballs in Japan

Several Leonid fireballs were successfully photographed by the Japanese Fireball Network and by other observers in Japan on 16 November, 1996. A totals of seven of these were simultaneously observed from two or more stations, from which the orbital and physical data were deduced. The radiant of these fireballs were very small, only 0.1°, similar to that of the 1991 Perseids. The 1996 Leonids showed a lower magnitude distribution index similar to those obtained in the 1961 and 1965 Leonids. All of these showers occurred before perihelion passage of the parent comet. We conclude that we have already encountered the elongated front part of the dust trail of the Leonid parent comet, where the trail is probably composed of larger dust particles. This revised version was published online in July 2006 with corrections to the Cover Date.     

Paleoseismological evidence for non-characteristic behavior of surface rupture associated with the 2004 Mid-Niigata Prefecture earthquake, central Japan

The 2004 Mid-Niigata Prefecture earthquake sequence (mainshock magnitude, M_JMA 6.8), which occurred in an active fold-and-thrust belt in northern central Japan, generated a small thrust surface rupture (< 20 cm of vertical displacement) along a previously unmapped northern extension of the active Muikamachi–Bonchi–Seien fault zone, on the eastern margin of the epicentral region. To better understand past seismic behavior of the rupture, we conducted a paleoseismic trenching study across the 10-cm-high west-side-up surface rupture at the foot of a pre-existing 1.8-m-high east-facing scarp, which probably resulted from past earthquake(s). A well-defined west-dipping thrust fault zone accompanied by drag folding and displacing the upper Pliocene to lower Pleistocene strata and the unconformably overlying upper Pleistocene (?) to Holocene strata was exposed. The principal fault zone is connected directly to the 2004 surface rupture. From the deformational characteristics of the strata and radiocarbon dating, we inferred that two large paleoseismic events occurred during the past 9000 years prior to the 2004 event. These two pre-2004 events have a nearly identical fault slip (at minimum, 1.5 m), which is ≥ 15 times that of the 2004 event (∼ 10 cm). These paleoseismic data, coupled with the geological and geomorphological features, suggest that the 2004 event represented non-characteristic behavior of the fault, which can potentially generate a more destructive earthquake accompanied by meter-scale surface displacement. This study provides insight into the interpretation of past faulting events and increases our understanding of rupture behavior.     

The role of meso-scale eddies in mixed layer deepening and mode water formation in the western North Pacific

Distributions of mixed layer depths around the centers of anti-cyclonic and cyclonic eddies in the North Pacific Ocean were composited by using satellite-derived sea surface height anomaly data and Argo profiling float data. The composite distributions showed that in late winter, deeper mixed layers were more (less) frequently observed inside the cores of the anti-cyclonic (cyclonic) eddies than outside. This relationship was the clearest in the region of 140°E–160°W and 35°N–40°N, where the temperature and salinity of the deep mixed layers were similar to those of the lighter variety of central mode water (L-CMW). A simple one-dimensional bulk mixed layer model showed that both strong sea-surface heat and momentum fluxes and weak preexisting stratification contributed to formation of the deep mixed layer. These conditions were associated with the anti-cyclonic eddies, suggesting that these eddies are important in the formation of mode waters, particularly L-CMW.     

Effectiveness of Neural Kriging for Three-Dimensional Modeling of Sparse and Strongly Biased Distribution of Geological Data with Application to Seafloor Hydrothermal Mineralization

Mathematical Geosciences - Three-dimensional modeling of geoscientific data of limited amounts and strongly biased locations is difficult and impractical using almost any method. To obtain a...     

A local void and the accelerating Universe

RCW 114 is a filamentary nebula of about 250 arcmin diameter. Based on its large diameter-to-filament-width ratio, the expansion velocity, distance and size of the shell, it has been suggested that RCW 114 is a supernova remnant in its momentum-conserving phase. Confirmation of this identification is important, as the large angular size and extensive optical emission of this object will allow for detailed study to improve our knowledge of supernova remnants and their interaction with the interstellar medium.
We have used the FLAIR instrument on the UK Schmidt Telescope to obtain optical spectra of several filaments in RCW 114. These confirm that the emission is being produced by the interaction of the shock wave of a supernova remnant with the surrounding interstellar medium. We also obtained narrow-band H α +[N  ii ] and [S  ii ] images to examine the spatial variation in ionization structure.     

Regeneration of silicate in the ocean

Regeneration of silicate in the Japan Sea, an example of semi-closed sea, was studied. In the Japan Sea Proper Water the apparent regenerative ratio of the nutrients was determined to be:O C N P Si=–289 (116)14.3181.It was assumed that the dissolved silicate present in sea water is grouped into three fractions; 1)preformed silicate of conservative nature, 2)oxidative silicate which dissolves in oxidation process of organisms with consumption of oxygen, and 3)non-oxidative silicate which dissolves without oxygen consumption. The dissolution rate ofnon-oxidative silicate in the Japan Sea Proper Water was estimated to be 0.07g-at. Si/l/yr from the data ofAOU values and assumed rates of oxygen consumption. This dissolution rate ofnon-oxidative silicate agreed with that obtained in the deep Pacific by the vertical advection diffusion model byKido andNishimura (1972).     

Fracture-zone conditions on a recently active fault: insights from mineralogical and geochemical analyses of the Hirabayashi NIED drill core on the Nojima fault, southwest Japan, which ruptured in the 1995 Kobe earthquake

An 1800-m-deep borehole into the Nojima fault zone was drilled at Nojima-Hirabayashi, Japan, after the 1995 Hyogo-ken Nanbu (Kobe) earthquake. Three possible fracture zones were detected at depths of about 1140, 1300, and 1800 m. To assess these fracture zones in this recently active fault, we analyzed the distributions of fault rocks, minerals, and chemical elements in these zones. The central fault plane in the shallowest fracture zone was identified by foliated blue-gray gouge at a depth of 1140 m. The degree of fracturing was evidently greater in the hanging wall than in the footwall. Minerals detected in this zone were quartz, orthoclase, plagioclase, and biotite, as in the parent rock (granodiorite), and also kaolinite, smectite, laumontite, stilbite, calcite, ankerite, and siderite, which are related to hydrothermal alteration. Biotite was absent in both the hanging wall and footwall across the central fault plane, but it was absent over a greater distance from the central fault plane in the hanging wall than in the footwall. Major element compositions across this zone suggested that hydrothermal alteration minerals such as kaolinite and smectite occurred across the central fault plane for a greater distance in the hanging wall than in the footwall. Similarly, H₂O+ and CO₂ had higher concentrations in the hanging wall than in the footwall. This asymmetrical distribution pattern is probably due to the greater degree of wall–rock fracturing and associated alteration in the hanging wall. We attributed the characteristics of this zone to fault activity and fluid–rock interactions. We analyzed the other fracture zones along this fault in the same way. In the fracture zone at about 1300 m depth, we detected the same kinds of hydrothermal alteration minerals as in the shallower zone, but they were in fewer samples. We detected relatively little H₂O+ and CO₂, and little evidence for movement of the major chemical elements, indicating little past fluid–rock interaction. In the fracture zone at about 1800 m depth, H₂O+ and CO₂ were very enriched throughout the interval, as in the fracture zone at about 1140 m depth. However, smectite was absent and chlorite was present, indicating the occurrence of chloritization, which requires a temperature of more than 200 °C. Only smectite can form under the present conditions in these fracture zones. The chloritization probably occurred in the past when the fracture zone was deeper than it is now. These observations suggest that among the three fracture zones, that at about 1140 m depth was the most activated at the time of the 1995 Hyogo-ken Nanbu (Kobe) earthquake.