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Processes and rates of weathering in representative tuff obtained from a Green Tuff region were directly examined using a new fluorescent approach. This approach was developed to visualize microscopically the microcracks and micropores that contribute to deterioration. The following observations were made. Progression of tuff weathering is caused by a delicate balance between chemical alteration and physical disintegration. Weathering occurs in many hidden microcracks and micropores not detected under natural light, but which can be clearly visualized under ultraviolet light. Water pathways, such as microcracks and cavities, accelerated the chemical alteration by increasing the effective surface area of rocks in contact with water. As the reaction proceeds, the constituent materials loosen and alteration products become widespread in the matrix. Secondary amorphous to poorly crystallized materials, such as iron hydroxide and aluminosilicate, precipitate on the fracture surfaces, slowing the progress of weathering. At the ultimate stage of weathering in tuff, all cracks and most of the micropores are filled with secondary materials. These observations on a microscopic scale during tuff weathering agree with the assessment of weathering obtained by measuring porosity, P-wave velocity and tensile strength. 相似文献
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Diffuse Emission of CO2 from Showa-Shinzan, Hokkaido, Japan: A Sign of Volcanic Dome Degassing 总被引：1，自引：0，他引：1
Pedro A. Hernández Kenji Notsu Hiromu Okada Toshiya Mori Masanori Sato Francisco Barahona Nemesio M. Pérez 《Pure and Applied Geophysics》2006,163(4):869-881
Two soil CO2 efflux surveys were carried out in September 1999 and June 2002 to study the spatial distribution of diffuse CO2 degassing and estimate the total CO2 output from Showa-Shinzan volcanic dome, Japan. Seventy-six and 81 measurements of CO2 efflux were performed in 1999 and 2002, respectively, covering most of Showa-Shinzan volcano. Soil CO2 efflux data showed a wide range of values up to 552 g m-2 d-1. Carbon isotope signatures of the soil CO2 ranged from -0.9‰ to -30.9‰, suggesting a mixing between different carbon reservoirs. Most of the study area showed CO2 efflux background values during the 1999 and 2002 surveys (B = 8.2 and 4.4 g m-2 d-1, respectively). The spatial distribution of CO2 efflux anomalies for both surveys showed a good correlation with the soil temperature, indicating a similar origin for the
extensive soil degassing generated by condensation processes and fluids discharged by the fumarolic system of Showa-Shinzan.
The total diffuse CO2 output of Showa-Shinzan was estimated to be about 14.0–15.6 t d-1 of CO2 for an area of 0.53 km2. 相似文献
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J.Arthur Snoke I.Selwyn Sacks Hiromu Okada 《Physics of the Earth and Planetary Interiors》1974,9(3):199-206
Various workers have constructed models to explain a class of anomalous arrivals at Peruvian and Chilean stations from deep-focus South American earthquakes. These arrivals are shear waves with a later arrival time, a higher frequency content, a longer duration and a lower apparent velocity than direct S. Our models assume that there is a sufficiently sharp discontinuity at the upper interface of the descending lithospheric slab between depths of 80 and 250 km to provide efficient reflection (≈0.1) for S-waves incident from below. The observed travel times require a single S-to-S reflection at this interface if the J-B velocity-depth model is modified to allow for 7% higher velocities down to a depth of 300 km (excluding the crust). The locus of required reflection points correlates well with the upper boundary of the observed seismicity (strike and dip angles within 5°) and Q for the proposed path is consistent with the frequency content of the anomalous arrivals. Thus the existence of these arrivals requires a dipping interface down to about 250 km, but, contrary to the wave-guide model of Isacks and Barazangi, cannot be used to infer a continuous lithospheric slab down to the deep-focus earthquakes (h #62; 500 km). 相似文献
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A number of statistical methods are typically used to effectively predict potential landslide distributions. In this study two multivariate statistical analysis methods were used （weights of evidence and logistic regression） to predict the potential distribution of shallow-seated landslides in the Kamikawachi area of Sabae City, Fukui Prefecture, Japan. First, the dependent variable （shallow-seated landslides） was divided into presence and absence, and the independent variables （environmental factors such as slope and altitude） were categorized according to their characteristics. Then, using the weights of evidence （WE） method, the weights of pairs comprising presence （w^＋（i）） or absence （w^-（i））, and the contrast values for each category of independent variable （evidence）, were calculated, Using the method that integrated the weights of evidence method and a logistic regression model, score values were calculated for each category of independent variable. Based on these contrast values, three models were selected to sum the score values of every gird in the study area. According to a receiver operating characteristic curve analysis （ROC）, model 2 yielded the best fit for predicting the potential distribution of shallow-seated landslide hazards, with 89% correctness and a 54.5% hit ratio when the occurrence probability （OP） of landslides was 70%. The model was tested using data from an area close to the study region, and showed 94% correctness and a hit ratio of 45.7% when the OP of landslides was 70%. Finally, the potential distribution of shallow-seated landslides, based on the OP, was mapped using a geographical information system. 相似文献
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Kazuaki Iishi Mitiko Miura Yuji Shiro Hiromu Murata 《Physics and Chemistry of Minerals》1983,9(2):61-66
On the basis of the polarizable-ion model (PIM) the effect of the width of the atomic electron distribution on the lattice dynamics of α-quartz was taken into account using the Birman method. The frequencies of optical mode, elastic constants and piezoelectric constants were reproduced using the parameters of this model (an effective charge z, a width parameter w, an electronic polarizability α, and force constants). The width parameter of oxygen atom was found to be about 0.59 Å, and the effective charge of the silicon atom 1.42 electron charges. 相似文献
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Youqing Chen Kota Watanabe Hiromu Kusuda Eishi Kusaka Mamoru Mabuchi 《Engineering Geology》2011,117(3-4):189-197
To examine the fatigue process of granite, cylindrical Westerly granite specimens, 10 mm in diameter and 20 mm in length, were subjected to a cyclic loading test under uniaxial compression with a maximum of 140 MPa at room temperature, and crack growth patterns within them were analyzed by microscopic observation and image analysis techniques. The fatigue process is divided into three characteristic stages; a primary stage in which the upper peak strain increases at a decelerating rate (stage I), a second stage with linearly slight increasing rate of strain following stage I (stage II), and the third and final stage in which the upper peak strain increases at an accelerating rate and culminates in specimen failure (stage III). A series of prefailure specimens, of which the stage in the fatigue process was decided by monitoring the strain behavior during the test, were retrieved. In addition, these specimens were compared with specimens stressed to close to the breaking strength by monotonic compression to examine the characteristic features of fatigue. The fluorescent method was applied to identify microcracks within the specimens. The advantage of this method is to provide quick and accurate identification of microcracks with an optical microscope. Microcracks are detected based on a marked difference in brightness under ultraviolet light irradiation because they are fully filled with acrylic resin mixed with a fluorescent substance in advance. Thin sections, including the axis of the specimen, 10 × 20 mm, were prepared for detailed observation after the pretreatment of the method.The results were as follows. At the initial degradation stage, distinguishing crack growth was identified in quartz grains. It is estimated that the slowdown of the strain growth rate at this stage was caused by the decrease in crack growth, that is, the portions with cracking potentiality were damaged at the first or early loading, and no further damage occurred immediately following the first damage. At the second stage, no significant crack growth in quartz grains was identified. On the other hand, in feldspar grains, development of cracks in a preferential direction, parallel to the loading direction, was observed. However, they did not grow into intergranular cracks by cutting across the grain boundaries during this stage. Consequently, it was found that a gradual progress of microcracks within feldspar grains was dominant during the second stage, and this is because the strain growth rate was in a steady and long state. At the final accelerated stage, many intergranular cracks running parallel to the loading direction were identified. It is obvious that these long cracks were formed mainly by the linking and growth of the intragranular cracks in feldspars, which were generated during the former stages. Their formation takes the fatigue process from the second stage to the final stage with a sharp increase in strain, and their further development seemed to lead the whole specimen to ultimate fatigue failure. 相似文献
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