Intermittent Phase Transitions in a Slider-block Model as a Mechanism for Earthquakes

— The aperiodic behavior of a two-dimensional stick-slip slider-block model of earthquakes is the subject of this study. The phenomenon of temporal phase transitions between creep and stick-slip motions is thoroughly analyzed and attributed to type-I intermittency. Asymmetry in the elastic forces is shown to play a key role in the emergence of complex behavior in the model. The unpredictability of chaotic bursts in the intermittent regime indicates potential difficulties for earthquake forecasting.     

Photometric and photo accoustic measurement of the absorbance of micro-organisms and its relation to the micro-organism-grain hypothesis

Absorption ofE. Coli and other micro-organisms are measured by the standard optical spectroscopy and by the photo-accoustic method. The former method does not yield an extinction peak at =220 nm but yields a weak one at =270 nm, while by the latter method absorption peaks at =220 nm and a weaker one at =270 nm have been found for the spore of Bacillus subtilis. The well-known amino-acid, triptophan shows absorption peaks at =220 and 280 nm. It is tentatively concluded that for the micro-organism model of interstellar grains to be viable, they may have to be spores rather than ordinary cells.     

A Test of Mining Simulations for Phosphorus Adjustment in a Limestone Quarry - Dynamic Programming Compared with a Genetic Algorithm

Limestone quarries where slaked lime is produced for steel makers have been urged to reduce the concentration of phosphorus in their products. In a few quarries in Japan, limestone blocks with low concentrations are blended with limestone blocks with high concentrations to stay below the limit of permitted phosphorus quality. The life of the quarry is extended as long as possible by this blending. Some quarries have a geological database with accurate records of the operations for phosphorus adjustment.However, the combination problem of these blocks typically is addressed by Dynamic Programming; that is, all combinations of possible limestone blocks are examined in the solving process; the combination numbers are so huge that the optimum combination cannot be solved in practical process times. Although it took 8 hours to solve for 600 blocks with a 2GHz high performance personal computer, it would take more than 36 days to approximately solve for 1200 blocks, and 3,378 days are estimated to solve 2,400 blocks. Therefore, a Genetic Algorithm was used to try and work out the optimum combination. First, blocks that can be removed are selected in the quarry and their removal sequence makes the genotype. The Order-base or the Grefenstette method was applied to avoid generating lethal genes in crossover. The fitness value was estimated by the number of products that included less than the permitted concentration of phosphorus.The GA process took less than 3 hours to solve for 1,200 blocks. Because the processing time is almost proportional to the block numbers, this GA method is practical in large quarries. Moreover, this method is easy to apply to other conditions in mining plans, such as environmental protection, noise prevention and eyesore problems. These problems are becoming important factors in quarries near towns in Japan.     

Holocene millennial-scale climate variations documented by multiple lake-level proxies in sediment cores from Hurleg Lake,Northwest China

Millennial-scale climate variability has not been well documented in arid northwest China due to the scarcity of high-resolution, well-dated paleoclimate records. Here we present multi-proxy records from sediment cores taken in freshwater Hurleg Lake on the northeastern Tibetan Plateau, which reveal millennial-scale lake-level and climate variations over the past 8,000 years. This high-elevation region is very sensitive to large-scale climate change, thus allowing us to better understand Holocene climate variations in East Asia. The lake-level record, derived from lithology, magnetic mineralogy, carbonate isotopes, ostracode shell isotopes and trace elements, X-ray fluorescence (XRF), and gray scale data, indicates a highly variable and generally dry climate from 7.8 to 1 ka (1 ka = 1,000 cal year BP), and a relatively stable and wet climate after 1 ka. Superimposed on this general trend, six dry intervals at 7.6–7.2 ka, 6.2–5.9 ka, 5.3–4.9 ka, 4.4–3.8 ka, 2.7–2.4 ka, and 1.7–1.1 ka were detected from the high-resolution carbonate content and XRF data. The generally dry climate between 7.8 and 1 ka was almost synchronous with the decrease of East Asian and Indian monsoon intensities shortly after 8 ka. The six dry intervals can be correlated with weak monsoon events recorded in the East Asia and Indian monsoon regions, as well as the North Atlantic cold events. Our data suggest that millennial-scale monsoon variations could cause highly variable climate conditions in arid northwest China during the Holocene. These millennial-scale climate variations may reflect changes in solar variation and/or changes in oceanic and atmospheric circulation.     

Submarine metamorphism of gabbros from the Mid-Cayman rise: An oxygen isotopic study

Oxygen isotopic compositions of minerals in 22 samples of submarine gabbros were determined. The gabbros were collected using the submersible Alvin from the 700 m vertical section of the rift-valley wall of the Mid-Cayman spreading center. Our study indicates that in the Mid-Cayman Rise seawater barely reached the bottom of the plutonic layer. Abundant seawater penetration (water/rock mass ratio > 1) was limited to the upper part of the plutonic layer. From the observed oxygen isotopic compositions of coexisting minerals, and from the experimental and empirical determinations of equilibrium fractionation of oxygen isotopes for mineral-water, and mineral-mineral pairs, we show the following: (1) pyroxene and olivine did not exchange oxygen with seawater, (2) plagioclase is in isotopic disequilibrium with pyroxene; (3) the rate of oxygen exchange in plagioclase was not slowed by the absence of cation exchange; (4) plagioclase and amphibole have exchanged oxygen with seawater or isotopically modified seawater (δ¹⁸O ≤ 3%.); and (5) amphibole has exchanged or acquired (during formation) hydrogen from seawater at 380°C ≤ T ≤ 600°C. The decrease in extent of isotopic exchange of plagioclase and the decrease in amphibole abundance with depth indicate that seawater flux decreased rapidly with depth (water/rock mass ratio falling from 1.7 to 0.2 over a 300 m interval).     

The examination of fracturing process subjected to triaxial compression test in Inada granite

The behavior of a granite subject to a triaxial compression test ranging from the prefailure stage to the postfailure stage was studied using a fluorescent technique from the geological point of view. Microscopic observations of the specimens at different stages showed changes in the failure process. The start of formation of new microcracks paralleled the compression direction through their propagation until the onset of faulting and ended with the failure of shear zones after the strength failure point. Pores chiefly identified in the feldspar increased in length and width in the early stages, but not in number. It seems that the effect of pore spaces did not have any effect of failure. The microcracks generated on angular edges of quartz or feldspar grains and around biotite grains with increasing compression force. The phenomenon appearing on the crystal boundaries among biotite and quartz or feldspar agrees with the result calculated based on the theory on stress fields with ellipsoidal inhomogeneity suggested by Eshelby.